# Artiklar

• Artikel i tidskrift

Söderström, Pär-Anders; Jaworski, G.; Dobon, J. J. Valiente; Nyberg, Johan et al.

### Neutron detection and gamma-ray suppression using artificial neural networks with the liquid scintillators BC-501A and BC-537

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 238-245, 2019.

#### Abstract

In this work we present a comparison between the two liquid scintillators BC-501A and BC-537 in terms of their performance regarding the pulse-shape discrimination between neutrons and gamma rays. Special emphasis is put on the application of artificial neural networks. The results show a systematically higher gamma-ray rejection ratio for BC-501A compared to BC-537 applying the commonly used charge comparison method. Using the artificial neural network approach the discrimination quality was improved to more than 95% rejection efficiency of gamma rays over the energy range 150 to 1000 keV for both BC-501A and BC-537. However, due to the larger light output of BC-501A compared to BC-537, neutrons could be identified in BC-501A using artificial neural networks down to a recoil proton energy of 800 keV compared to a recoil deuteron energy of 1200 keV for BC-537. We conclude that using artificial neural networks it is possible to obtain the same gamma-ray rejection quality from both BC-501A and BC-537 for neutrons above a low-energy threshold. This threshold is, however, lower for BC-501A, which is important for nuclear structure spectroscopy experiments of rare reaction channels where low-energy interactions dominates.

• Artikel i tidskrift

Nair, Shankar Sunil; Perotti, Elisabetta; Leupold, Stefan

### Constraining P and CP violation in the main decay of the neutral Sigma hyperon

Ingår i Physics Letters B, s. 535-541, 2019.

#### Abstract

On general grounds based on quantum field theory the decay amplitude for Sigma(0) -> Lambda gamma consists of a parity conserving magnetic and a parity violating electric dipole transition moment. Because of the subsequent self-analyzing weak decay of the Lambda hyperon the interference between magnetic and electric dipole transition moment leads to an asymmetry in the angular distribution. Comparing the decay distributions for the Sigma(0) hyperon and its antiparticle gives access to possible C and CP violation. Based on flavor SU(3) symmetry the present upper limit on the neutron electric dipole moment can be translated to an upper limit for the angular asymmetry. It turns out to be far below any experimental resolution that one can expect in the foreseeable future. Thus any true observation of a CP violating angular asymmetry would constitute physics beyond the standard model, even if extended by a CP violating QCD theta-vacuumangle term.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurements of e(+)e(-)-> (KSK +/-)-K-0 pi(-/+)pi(0) and (KSK +/-)-K-0 pi(-/+)eta at center-of-mass energies from 3.90 to 4.60 GeV

Ingår i Physical Review D, 2019.

#### Abstract

Using 5.2 fb(-1) e(+)e(-) annihilation data samples collected with the BESIII detector, we measure the cross sections of e(+)e(-)->(KSK +/-)-K-0 pi(-/+)pi(0) and (KSK +/-)-K-0 pi(-/+)eta at center-of-mass energies from 3.90 to 4.60 GeV. In addition, we search for the charmoniumlike resonance Y(4260) decays into (KSK +/-)-K-0 pi(-/+)pi(0) and (KSK +/-)-K-0 pi(-/+)eta and Z(c)(0,+/-) (3900) decays into (KSK +/-)-K-0 pi(-/+)(,0) and (KSK +/-)-K-0 eta. Corresponding upper limits are provided since no clear signal is observed.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Study of the Dalitz decay J/psi -> e(+)e(-)eta

Ingår i Physical Review D, 2019.

#### Abstract

We study the electromagnetic Dalitz decay J/psi -> e(+)e(-)eta and search for dielectron decays of a dark gauge boson (gamma') in J/psi -> gamma'eta with the two q decay modes eta -> gamma gamma and eta -> pi(+)pi(-)pi(0) using (1310.6 +/- 7.0) x 10(6) J/psi events collected with the BESIII detector. The branching fraction of J/psi -> e(+)e(-)eta is measured to be (1.43 +/- 0.04(stat) +/- 0.06(syst)) x 10(-5), with a precision that is improved by a factor of 1.5 over the previous BESIII measurement. The corresponding dielectron invariant mass dependent modulus square of the transition form factor is explored for the first time, and the pole mass is determined to be Lambda = 2.84 +/- 0.11(stat) +/- 0.08(syst) GeV/c(2). We find no evidence of gamma' production and set 90% confidence level upper limits on the product branching fraction B(J/psi -> gamma'eta) x B(gamma' -> e(+)e(-)) as well as the kinetic mixing strength between the standard model photon and gamma' in the mass range of 0.01 <= m(gamma') <= 2.4 GeV/c(2).

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Search for a strangeonium-like structure Z(s) decaying into phi pi and a measurement of the cross section e(+)e(-) -> phi pi pi

Ingår i Physical Review D, 2019.

#### Abstract

Using a data sample of e(+)e(-) collision data corresponding to an integrated luminosity of 108 pb(-1) collected with the BESIII detector at a center-of-mass energy of 2.125 GeV, we study the process e(+)e(-) -> phi pi pi and search for a strangeoniumlike structure Z(s) decaying into phi pi. No signal is observed in the phi pi mass spectrum. Upper limits on the cross sections for Z(s) production at the 90% confidence level are determined. In addition, the cross sections of e(+)e(-) -> phi pi(+)pi(-) and e(+)e(-) -> phi pi(0)pi(0) at 2.125 GeV are measured to be (436.2 +/- 6.4 +/- 30.1) pb and (237.0 +/- 8.6 +/- 15.4) pb, respectively, where the first uncertainties are statistical and the second systematic.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Study of the D-0 -> K-mu(+)nu(mu) Dynamics and Test of Lepton Flavor Universality with D-0 -> K(-)l(+)nu(l) Decays

Ingår i Physical Review Letters, 2019.

#### Abstract

Using e(+)e(-) annihilation data of 2.93 fb(-1) collected at center-of-mass energy root s = 3.773 GeV with the BESIII detector, we measure the absolute branching fraction of D-0 -> K-mu(+)nu(mu) with significantly improved precision: BD0 -> K-mu+nu mu = (3.413 +/- 0.019(stat) +/- 0.035(syst))%. Combining with our previous measurement of BD0 -> K-e+nu e, the ratio of the two branching fractions is determined to be BD0 -> K-mu+nu mu/BD0 -> K-e+nu e = 0.974 +/- 0.007(stat) +/- 0.012(syst), which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. A study of the ratio of the two branching fractions in different four-momentumtransfer regions is also performed, and no evidence for lepton flavor universality violation is found with current statistics. Taking inputs from global fit in the standard model and lattice quantum chromodynamics separately, we determine f(+)(K)(0) = 0.7327 +/- 0.0039(stat) +/- 0.0030(syst) and vertical bar V-cs vertical bar = 0.955 +/- 0.005(stat) +/- 0.004(syst) +/- 0.024(LQCD).

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of e(+) e(-) -> eta Y(2175) at center-of-mass energies above 3.7 GeV

Ingår i Physical Review D, 2019.

#### Abstract

The state Y(2175) is observed in the process e(+)e(-) -> eta Y(2175) with a statistical significance larger than 10 standard deviations using the data collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies between 3.7 and 4.6 GeV. This is the first observation of the Y(2175) in this process. The mass and width of the Y(2175) are determined to be (2135 +/- 8 +/- 9) MeV/e(2) and (104 +/- 24 +/- 12) MeV, respectively, and the production cross section (sigma) of e(+)e(-) -> eta Y(2175) -> eta phi f(0)(980) -> eta phi pi(+)pi(-) is at the several hundred femtobarn level. No significant signal for the process e(+)e(-) -> eta'Y(2175) is observed and the upper limit on sigma(e(+)e(-) -> eta'Y(2175))/sigma(e(+)e(-) -> eta Y(2175)) is estimated to be 0.43 at the 90% confidence level. We also search for psi(3686) -> eta Y(2175). No significant signal is observed, indicating a strong suppression relative to the corresponding J/psi decay, in violation of the "129% rule".

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of OZI-suppressed decays chi(cJ) -> omega phi

Ingår i Physical Review D, 2019.

#### Abstract

Decays chi(cJ)(J = 0, 1, 2) -> omega phi are studied using (448.1 +/- 2.9) x 10(6)psi(3686) events collected with the BESIII detector in 2009 and 2012. In addition to the previously established chi(c0) -> omega phi, the first observation of chi(c1) -> omega phi is reported in this paper. The measured product branching fractions are B(psi(3686) -> gamma chi(c0)) x B(chi(c0) -> omega phi) = (13.83 +/- 0.70 +/- 1.01) x 10(-6) and B(psi(3686) -> gamma chi(c1)) x B(chi(c1) -> omega phi) = (2.67 +/- 0.31 +/- 0.27) x 10(-6), and the absolute branching fractions are B(chi(c0) -> omega phi) = (13.84 +/- 0.70 +/- 1.08) x 10(-5) and B(chi(c1) -> omega phi) = (2.80 +/- 0.32 +/- 0.30) x 10(-5). We also find strong evidence for chi(c2) -> omega phi with a statistical significance of 4.8 sigma, and the corresponding product and absolute branching fractions are measured to he B(psi(3686) -> gamma chi(c2)) x B(chi(c2) -> omega phi) = (0.91 +/- 0.23 +/- 0.12) x 10(-6) and B(chi(c2) -> omega phi) = (1.00 +/- 0.25 +/- 0.14) x 10(-5). Here, the first errors are statistical and the second ones systematic.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Study of the decay D0→¯K0π−e+νe

Ingår i Physical Review D, 2019.

#### Abstract

We report a study of the decay D-0 -> (K) over bar (0)pi(-)e(+)nu(e) based on a sample of 2.93 fb(-1) e(+)e(-) annihilation data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. The total branching fraction is determined to be B(D-0 -> (K) over bar (0)pi(-)e(+)nu(e)) = (1.434 +/- 0.029(stat.) +/- 0.032(syst.))%, which is the most precise to date. According to a detailed analysis of the involved dynamics, we find this decay is dominated with the K*(892)(-) contribution and present an improved measurement of its branching fraction to be B(D-0 -> K*(892)(-)e(+)nu(e) = (2.033 +/- 0.046(stat.) +/- 0.047(syst.))%. We further access their hadronic form-factor ratios for the first time as r(V) = V(0)/A(1)(0) = 1.46 +/- 0.07(stat.) +/- 0.02(syst.) and r(2) = A(2)(0)/A(1)(0) = 0.67 +/- 0.06(stat.) +/- 0.01(syst.). In addition, we observe a significant (K) over bar (0)pi(-) S-wave component accounting for (5.51 +/- 0.97(stat.) +/- 0.62(syst.))% of the total decay rate.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurement of B(J/ψ→η'e+e−) and search for a dark photon

Ingår i Physical Review D, 2019.

#### Abstract

Using a data sample of (1310.6 +/- 7.0) x 10(6) J/psi decay events collected with the BESIII detector at BEPCII, we study the electromagnetic Dalitz decay J/psi -> eta ' e(+)e(-) with two dominant eta' decay modes, eta' -> gamma pi(+)pi(-) and eta' -> pi(+)pi(-)eta . The branching fraction is determined to be B(J/psi -> eta ' e(+)e(-)) = (6.59 +/- 0.07 +/- 0.17) x 10(-5), which improves in precision by a factor of 2 over the previous BESIII measurement. A search for the dark photon (gamma') is performed via J/psi -> eta'gamma',gamma' -> e(+)e(-). Excluding the w and phi mass regions, no significant signal is observed in the mass range from 0.1 to 2.1 GeV/e2. We set upper limits at the 90% confidence level on B(J/psi -> eta 'gamma') x B(gamma' -> e(+)e(-)), B(J/psi -> eta 'gamma') and the mixing strength as a function of dark photon mass. This is among the first searches for dark photons in charmonium decays.

Open access
• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Examination of the production of an isotensor dibaryon in the pp -> pp pi(+)pi(-) reaction

Ingår i Physical Review C, 2019.

#### Abstract

The quasifree pp -> pp pi(+)pi(-) reaction has been measured by means of pd collisions at T-p = 1.2 GeV using the WASA detector setup at COSY enabling exclusive and kinematically complete measurements. Total and differential cross sections have been extracted for the energy region T-p = 1.08-1.36 GeV (root s = 2.35-2.46 GeV) covering thus the regions of N* (1440 ) and Delta(1232)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange as well as isospin relations based on the pp -> pp pi(0)pi(0) data underpredict substantially the measured total cross section. The calculations are also at variance with specific experimental differential cross sections. An isotensor Delta N dibaryon resonance with I(J(P)) = 2(1(+) ) produced associatedly with a pion is able to overcome these deficiencies. Such a dibaryon was predicted by Dyson and Xuong [Phys. Rev. Lett. 13, 815 (1964)] and more recently calculated by A. Gal and H. Garcilazo [Nucl. Phys. A 928, 73 (2014)].

• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurement of e(+) e(-) -> K+ K- cross section at root s=2.00-3.08 GeV

Ingår i Physical Review D, 2019.

#### Abstract

The cross section of the process e(+) e(-) -> K+ K- is measured at a number of center-of-mass energies root s from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of M = 2239.2 +/- 7.1 +/- 11.3 MeV/c(2) and a width of Gamma = 139.8 +/- 12.3 +/- 20.6 MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the timelike electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of D-s(+) -> p(n)over-bar and confirmation of its large branching fraction

Ingår i Physical Review D, 2019.

#### Abstract

The baryonic decay D-s(+) -> p (n) over bar is observed, and the corresponding branching fraction is measured to be (1.21 +/- 0.10 +/- 0.05) x 10(-3), where the first uncertainty is statistical and second systematic. The data sample used in this analysis was collected with the BESIII detector operating at the BEPCII e(+)e(-) double-ring collider with a center-of-mass energy of 4.178 GeV and an integrated luminosity of 3.19 fb(-1). The result confirms the previous measurement by the CLEO Collaboration and is of greatly improved precision. This result will improve our understanding of the dynamical enhancement of the W-annihilation topology in the charmed meson decays.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of psi(3686) -> p(p)over-bar eta ' and improved measurement of J/psi -> p(p)over-bar eta '

Ingår i Physical Review D, 2019.

#### Abstract

We observe the process psi(3686) -> p (p) over bar eta' for the first time, with a statistical significance higher than 10 sigma, and measure the branching fraction of J/psi -> p (p) over bar eta' with an improved accuracy compared to earlier studies. The measurements are based on 4.48 x 10(8) psi(3686) and 1.31 x 10(9) J/psi events collected by the BESIII detector operating at the BEPCII. The branching fractions are determined to be B(psi(3686) -> p (p) over bar eta') = (1.10 +/- 0.10 +/- 0.08) x 10(-5) and B(J/psi -> p (p) over bar eta' = (1.26 +/- 0.02 +/- 0.07) x 10(-4), where the first uncertainties are statistical and the second ones systematic. Additionally, the eta - eta' mixing angle is determined to be -24 degrees +/- 11 degrees based on psi(3686) -> p (p) over bar eta', and -24 degrees +/- 9 degrees based on J/psi -> p (p) over bar eta', respectively.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### First Measurement of the Form Factors in D-s(+) -> K(0)e(+)nu(e) and D-s(+) -> K*(0)e(+)nu(e) Decays

Ingår i Physical Review Letters, 2019.

#### Abstract

We report on new measurements of Cabibbo-suppressed semileptonic D-s(broken vertical bar) decays using 3.19 fb(-1) of e(broken vertical bar)e(-) annihilation data sample collected at a center-of-mass energy of 4.178 GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions B(D-s(+) -> K(0)e(+)nu(e)) = [3.25 +/- 0.38(stat) +/- 0.16(syst)] x 10(-3) and B(D-s(+) -> K*(0)e(+)nu(e)) = [2.37 +/- 0.26(stat) +/- 0.20(syst)] x 10(-3), which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For D-s(+) -> K(0)e(+)nu(e), we obtain f(+)(0) = 0.720 +/- 0.084(stat) +/- 0.013(syst), and for D-s(+) -> K*(0)e(+)nu(e), we find form-factor ratios r(V) = V(0)/A(1)(0) = 1.67 +/- 0.34(stat) +/- 0.16(syst) and r(2) = A(2)(0)/A(1)(0) = 0.77 +/- 0.28(stat) +/- 0.07(syst).

Open access
• Artikel i tidskrift

Davies, P. J.; Park, J.; Grawe, H.; Wadsworth, R. et al.

### Toward the limit of nuclear binding on the N = Z line: Spectroscopy of Cd-96

Ingår i Physical Review C, 2019.

#### Abstract

A gamma -decaying isomeric state (tau(1/2) = 197(-17)(+19) ns) has been identified in Cd-96, which is one alpha particle away from the last known bound N = Z nucleus, Sn-100. Comparison of the results with shell-model calculations has allowed a tentative experimental level scheme to be deduced and the isomer to be interpreted as a medium-spin negative-parity spin trap based on the coupling of isoscalar (T = 0) and isovector (T = 1) neutron-proton pairs. The data also suggest evidence for the population of a 9(+) T = 1 state, which is predicted by shell-model calculations to be yrast. Such a low-lying T = 1 state, which is unknown in lighter mass even-even self-conjugate nuclei, can also be interpreted in terms of the coupling of T = 0 and T = 1 neutron-proton pairs.

• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Study of electromagnetic Dalitz decays chi(cJ )-> mu(+)mu(-) J/psi

Ingår i Physical Review D, 2019.

#### Abstract

Using 4.48 x 10(8) psi(3686) events collected with the BESIII detector, we search for the decays chi(cJ) ->mu(+)mu(- )J/psi through the radiative decays psi(3686) -> gamma chi(cJ), where J = 0, 1, 2. The decays chi(c1,2) -> mu(+)mu(-)J/psi are observed, and the corresponding branching fractions arc measured to be B(chi(c1) -> mu(+)mu(-) J/psi) = (2.51 +/- 0.18 +/- 0.20) x 10(-4) and B(chi(c2 )-> mu(+)mu(- )J/psi) = (2.33 +/- 0.18 +/- 0.29) x 10(-4), where the first uncertainty is statistical and the second one systematic. No significant chi(c0 )-> mu(+)mu(- )J/psi decay is observed, and the upper limit on the branching fraction is determined to be 2.0 x 10(-5) at 90% confidence level. Also, we present a study of dimuon invariant mass dependent transition form factor for the decays chi(c1,2 )->mu(+)mu(- )J/psi.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Precision Measurement of the Branching Fractions of eta ' Decays

Ingår i Physical Review Letters, 2019.

#### Abstract

Based on a sample of (1310.6 +/- 7.0) x 10(6)J/psi events collected with the BESIII detector, we present measurements of J=. and. 0 absolute branching fractions using the process J/psi -> gamma eta'. By analyzing events where the radiative photon converts into an e(+)e(-) pair, the branching fraction for J/psi -> gamma eta'is measured to be (5.27 +/- 0.03 +/- 0.05) x 10(-3). The absolute branching fractions of the five dominant decay channels of the. 0 are then measured for the first time and are determined to be B(eta' -> gamma pi(+)pi(-))= (29.90 +/- 0.03 +/- 0.55)%, B(eta' -> eta pi(+)pi(-)) = (41.24 +/- 0.08 +/- 1.24)%, B(eta' -> gamma gamma) = (21.36 +/- 0.10 +/- 0.92)%, B(eta' -> gamma omega) = (2.489 +/- 0.018 +/- 0.074)%, and B(eta' -> gamma gamma) = (2.331 +/- 0.012 +/- 0.035)%, where the first uncertainties are statistical and the second systematic.

Open access
• Artikel i tidskrift

Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Precision measurements of the e+e- → K0SK±π∓ Born cross sections at center-of-mass energies between 3.8 and 4.6 GeV

Ingår i Physical Review D, 2019.

#### Abstract

Using data samples collected by the BESIII detector operating at the BEPCII storage ring, we measure the e+e- → K0SK±π Born cross sections at center-of-mass energies between 3.8 and 4.6 GeV, corresponding to a luminosity of about 5.0 fb-1. The results are compatible with the BABAR measurements, but with the precision significantly improved. A simple 1/sn dependence for the continuum process can describe the measured cross sections, but a better fit is obtained by an additional resonance near 4.2 GeV, which could be an excited charmonium or a charmoniumlike state.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Search for rare decay J/psi -> phi e(+)e(-)

Ingår i Physical Review D, 2019.

#### Abstract

Using a data sample of 448.1 x 10(6) psi(3686) events collected at root s = 3.686 GeV with the BESIII detector at the Beijing Electron-Positron Collider II, we search for the rare decay J/psi -> phi e(+)e(-) via psi(3686) -> pi(+)pi(-) J/psi. No signal events are observed and the upper limit on the branching fraction is set to be B(J/psi -> phi e(+)e(-)) < 1.2 x 10(-7) at the 90% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurements of the absolute branching fractions and CP asymmetries for D+ -> (KS,LK+)-K-0 (pi(0))

Ingår i Physical Review D, 2019.

#### Abstract

Using e(+)e(-) collision data corresponding to an integrated luminosity of 2.93 fb(-1) taken at a center-of-mass energy of 3.773 GeV with the BESIII detector, we determine the absolute branching fractions B(D+ -> (KSK+)-K-0) = (3.02 +/- 0.09 +/- 0.08) x 10(-3), B(D+ -> (KSK+)-K-0 pi(0)) = (5.07 +/- 0.19 +/- 0.23) x 10(-3), B(D+ -> (KLK+)-K-0) = (3.21 +/- 0.11 +/- 0.11) x 10(-3), and B(D+ -> (KLK+)-K-0 pi(0)) = (5.24 +/- 0.22 +/- 0.22) x 10(-3), where the first and second uncertainties are statistical and systematic, respectively. The branching fraction B(D+ -> (KSK+)-K-0) is consistent with the world average value and the other three branching fractions are measured for the first time. We also measure the CP asymmetries for the four decays and do not find a significant deviation from zero.

Open access
• Artikel i tidskrift

Singh, B.; Calén, Hans; Andersson, Walter Ikegami; Johansson, Tord et al.

### Technical design report for the (P)over-barANDA Barrel DIRC detector

Ingår i Journal of Physics G, 2019.

#### Abstract

The (P) over bar ANDA (anti-Proton ANnihiliation at DArmstadt) experiment will be one of the four flagship experiments at the new international accelerator complex FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. (P) over bar ANDA will address fundamental questions of hadron physics and quantum chromodynamics using high-intensity cooled antiproton beams with momenta between 1.5 and 15 GeV/c and a design luminosity of up to 2 x 10(32) cm(-2) S-1. Excellent particle identification (PID) is crucial to the success of the (P) over bar ANDA physics program. Hadronic PID in the barrel region of the target spectrometer will be performed by a fast and compact Cherenkov counter using the detection of internally reflected Cherenkov light (DIRC) technology. It is designed to cover the polar angle range from 22 degrees to 140 degrees and will provide at least 3 standard deviations (s.d.) pi/K separation up to 3.5 GeV/c, matching the expected upper limit of the final state kaon momentum distribution from simulation. This documents describes the technical design and the expected performance of the (P) over bar ANDA Barrel DIRC detector. The design is based on the successful BaBar DIRC with several key improvements. The performance and system cost were optimized in detailed detector simulations and validated with full system prototypes using particle beams at GSI and CERN. The final design meets or exceeds the PID goal of clean pi/K separation with at least 3 s.d. over the entire phase space of charged kaons in the Barrel DIRC.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of D+→f0(500)e+νe and Improved Measurements of D→ρe+νe

Ingår i Physical Review Letters, 2019.

#### Abstract

Using a data sample corresponding to an integrated luminosity of 2.93 fb(-1) recorded by the BESIII detector at a center-of-mass energy of 3.773 GeV, we present an analysis of the decays D-0 -> pi(-) pi(0) e(vertical bar) nu(e) and D-vertical bar -> pi(-) pi(vertical bar) e(vertical bar) nu(e). By performing a partial wave analysis, the pi(vertical bar) pi(-) S-wave contribution to D-vertical bar -> pi(-) pi(vertical bar) e(vertical bar) nu(e) is observed to be (25.7 +/- 1.6 +/- 1.1)% with a statistical significance greater than 10 sigma, besides the dominant P-wave contribution. This is the first observation of the S-wave contribution. We measure the branching fractions B(D0 -> rho(-) e(+) nu(e)) = (1.445 +/- 0.058 +/- 0.039) x 10(-3), B(D+ -> rho(0) e(+) nu(e)) = (1.860 +/- 0.070 +/- 0.061) x 10(-3), and B(D+ -> f(0)(500)e(+) nu(e),f(0)(500) -> pi(+) pi(-)) = (6.30 +/- 0.43 +/- 0.32) x 10(-4). An upper limit of B(D+ -> f(0)(980)e(+) nu(e),f(0)(980)-> pi(+) pi(-)) < 2.8 x 10(-5) is set at the 90% confidence level. We also obtain the hadronic form factor ratios of D -> rho e(+) nu(e) at q(2) = 0 assuming the single-pole dominance parametrization: r(V) ={[V(0)]/[A(1)(0)]}=1.695 +/- 0.083 +/- 0.051, r(2) = {[A(2)(0)]/[A(1)(0)]} = 0.845 +/- 0.056 +/- 0.039.

Open access
• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Determination of the Pseudoscalar Decay Constant f(Ds)(+) via D-s(+) -> mu(+)nu(mu)

Ingår i Physical Review Letters, 2019.

#### Abstract

Using a 3.19 fb(-1) data sample collected at an e(+)e(-) center-of-mass energy of E-cm = 4.178 GeV with the BESIII detector, we measure the branching fraction of the leptonic decay D-s(+) -> mu(+)nu(mu) to be BDs+ -> mu+nu mu = (5.49 +/- 0.16(stat) +/- 0.15(syst)) x 10(-3). Combining our branching fraction with the masses of the D-s(+) and mu(+) and the lifetime of the D-s(+), we determine f(Ds+)vertical bar V-cs vertical bar = 246.2 +/- 3.6(stat) +/- 3.5(syst) MeV. Using the c -> s quark mixing matrix element vertical bar V-cs vertical bar determined from a global standard model fit, we evaluate the D-s(+) decay constant f(Ds+) = 252.9 +/- 3.7(stat) +/- 3.6(syst) MeV. Alternatively, using the value of f(Ds+) calculated by lattice quantum chromodynamics, we find vertical bar V-cs vertical bar = 0.985 +/- 0.014(stat) +/- 0.014(syst). These values of BDs+ -> mu+nu mu, f(Ds+)vertical bar V-cs vertical bar, f(Ds+) and vertical bar V-cs vertical bar are each the most precise results to date.

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Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurement of the absolute branching fractions of Lambda(+)(c) -> Lambda eta pi(+) and Sigma(1385) (+) eta

Ingår i Physical Review D, 2019.

#### Abstract

We study the decays Lambda(+)(c) -> Lambda eta pi(+) and Sigma(1385)(+)eta based on Lambda(+)(c)(Lambda) over bar (c) pairs produced in e(+)e(-) collisions at a center-of-mass energy of root s = 4.6 GeV, corresponding to an integrated luminosity of 567 pb(-1). The data sample was accumulated with the BESIII detector at the BEPCII collider. The branching fractions are measured to be beta(Lambda(+)(c) -> Lambda eta pi(+)) = (1.84 +/- 0.21 (stat) +/- 0.15(syst))% and B(Lambda(+)(c) -> Sigma(1385)(+) eta) = (0.91 +/- 0.18 (stat) +/- 0.09 (syst))%, constituting the most precise measurements to date.

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Perotti, Elisabetta; Fäldt, Göran; Kupsc, Andrzej; Leupold, Stefan et al.

### Polarization observables in e(+) e(-) annihilation to a baryon-antibaryon pair

Ingår i Physical Review D, 2019.

#### Abstract

Using the helicity formalism of Jacob and Wick, we derive spin density matrices of baryon antibaryon pairs produced in e(+)e(-) annihilation. We consider the production of pairs with spins 1/2 + (1/2) over bar, 1/2 + (3/2) over bar (+c.c.) and 3/2 + (3/2) over bar. We provide modular expressions to include chains of weak hadronic two-body decays of the produced hyperons. The expressions are suitable for the analysis of high statistics data from J/psi and psi(2S) ecays at e(+) e(-) colliders, by fits to the fully differential angular distributions of the measured particles. We illustrate the method by examples, such as the inclusive measurement of the e(+) e(-) -> psi(2S) -> Omega(-)(Omega) over bar (+) process where one decay chain Omega(-) -> AK(-) followed by A -> p pi(-) is considered. Finally, we show that the inclusive angular distributions can be used to test spin assignment of the produced baryons.

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Search for the decay D-s(+) -> gamma e (+) nu(e)

Ingår i Physical Review D, 2019.

#### Abstract

A search for the rare radiative leptonic decay D-s(+) -> gamma e(+)nu(e) is performed for the first time using electron-positron collision data corresponding to an integrated luminosity of 3.19 fb(-1), collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. No evidence for the D-s(+) -> gamma e(+)nu(e) decay is seen, and an upper limit of beta(D-s(+) -> gamma e(+)nu(e)) < 1.3 x 10(-4) is set on the partial branching fraction at a 90% confidence level for radiative photon energies E-gamma* > 0.01 GeV.

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Evidence of a Resonant Structure in the e(+) e(-) -> pi(+) (DD)-D-0*(-) Cross Section between 4.05 and 4.60 GeV

Ingår i Physical Review Letters, 2019.

#### Abstract

The cross section of the process e(+) e(-) -> pi(+) (DD)-D-0*(-) for center-of-mass energies from 4.05 to 4.60 GeV is measured precisely using data samples collected with the BESIII detector operating at the BEPCII storage ring. Two enhancements are clearly visible in the cross section around 4.23 and 4.40 GeV. Using several models to describe the dressed cross section yields stable parameters for the first enhancement, which has a mass of 4228.6 +/- 4.1 +/- 6.3 MeV/c(2) and a width of 77.0 +/- 6.8 +/- 6.3 MeV, where the first uncertainties are statistical and the second ones are systematic. Our resonant mass is consistent with previous observations of the Y(4220) state and the theoretical prediction of a D (D) over bar (1)(2420) molecule. This result is the first observation of Y(4220) associated with an open-charm final state. Fits with three resonance functions with additional Y(4260), Y(4320), Y(4360), psi(4415), or a new resonance do not show significant contributions from either of these resonances. The second enhancement is not from a single known resonance. It could contain contributions from psi(4415) and other resonances, and a detailed amplitude analysis is required to better understand this enhancement.

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurement of the Dynamics of the Decays D-s(+ )-> eta(('))e(+)nu(e)

Ingår i Physical Review Letters, 2019.

#### Abstract

Using e(+)e(-) annihilation data corresponding to an integrated luminosity of 3.19 fb(-1) collected at a center-of-mass energy of 4.178 GeV with the BESIII detector, we measure the absolute branching fractions BDs+->eta e+nu e = (2.323 +/- 0.063(stat) +/- 0.063(syst))% and BDs+->eta'e+nu e = (0.824 +/- 0.073(stat) +/- 0.027(syst))% via a tagged analysis technique, where one D-s is fully reconstructed in a hadronic mode. Combining these measurements with previous BESIII measurements of B-D+->eta(')e+(nu e),the eta - eta' mixing angle in the quark flavor basis is determined to be phi(P) = (40.1 +/- 2.1(stat) +/- 0.7(syst))degrees. From the first measurements of the dynamics of Ds+ -> eta(')e(+)nu(e) decays, the products of the hadronic form factors f(+)(eta('))(0) and the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cs vertical bar are determined with different form factor parametrizations. For the two-parameter series expansion, the results are f(+)(eta) (0) vertical bar V-cs vertical bar = 0.4455 +/- 0.0053(stat) +/- 0.0044(syst) and f(+)(eta)' (0) vertical bar V-cs vertical bar and = 0.477 +/- 0.049(stat) +/- 0.011(syst).

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of e(+)e(-)-> D-s(+)(D)over-bar(()*()0) K- and study of the P-wave D-s mesons

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2019.

#### Abstract

Studies of e(+)e(-)-> D-s(+)(D) over bar (()*K-)0(-) and the p-wave charmed-strange mesons are performed based on an e(+)e(-) collision data sample corresponding to an integrated luminosity of 567 pb(-1) collected with the BESIII detector at root s = 4.600 GeV. The processes of e(+)e(-)-> D-s(+)(D ) over bar*K-0(-) and D-s(+)(D ) over bar K-0(-) are observed for the first time and are found to be dominated by the modes Ds+Ds1 (2536)(-) and Ds(+)Ds*(s2) (2573)(-), respectively. The Born cross sections are measured to be sigma(B)(e(+)e( -)-> D-s(+)(D ) over bar K-*0(-) (10.1 +/- 2.3 +/- 0.8) pb and D-s(+)(D ) over bar K-0(-) = (19.4 +/- 2.3 +/- 1.6) pb, and the products of Born cross section and the decay branching fraction are measured to be sigma(B)(e(+)e( -)-> Ds+Ds1(2536)(-)+c.c).B(D-s1(2536)(-) = ( 7.5 +/- 1.8 +/- 0.7) pb and sigma(B)(e(+)e(-)-> Ds+Ds1+(2573)(-)c.c.). B(D-s1(2573)(-)-> (D ) over bar*K-0(-)) = (19.7 +/- 2.9 +/- 2.0) pb. For the D-s1(2536)(-) and D-s2(2573)(-) mesons, the masses and widths are measured to be M(D-s1(2536)(-)) = (2537.7 +/- 0.5 +/- 3.1) MeV/c(2), Gamma(D-s1(2536)(-)) = (1.7 +/- 1.2 +/- 0.6)MeV, and M(D-s2*(2573)(-)) = (2570.7 +/- 2.0 +/- 1.7) MeV/c(2), Gamma(D-s2(2573)(-)) = (17.2 +/- 3.6 +/- 1.1) MeV. The spin-parity of the D-s2*(2573)(-) meson is determined to be J(P) = 2(+). In addition, the processes e(+)e(-)-> D-s(+)(D ) over bar*K-0(-) are searched for using the data samples taken at four (two) center-of-mass energies between 4.416 (4.527) and 4.575 GeV, and upper limits at the 90% confidence level on the cross sections are determined.

• Artikel i tidskrift

Barucca, G.; Martin, A.; Akram, Adeel; Calén, Hans et al.

### Precision resonance energy scans with the PANDA experiment at FAIR: Sensitivity study for width and line shape measurements of the X(3872)

Ingår i European Physical Journal A, 2019.

#### Abstract

This paper summarises a comprehensive Monte Carlo simulation study for precision resonance energy scan measurements. Apart from the proof of principle for natural width and line shape measurements of very narrow resonances with PANDA, the achievable sensitivities are quantified for the concrete example of the charmonium-like X(3872) state discussed to be exotic, and for a larger parameter space of various assumed signal cross-sections, input widths and luminosity combinations. PANDA is the only experiment that will be able to perform precision resonance energy scans of such narrow states with quantum numbers of spin and parities that differ from JPC=1--.

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurement of the phase between strong and electromagnetic amplitudes of J/Psi decays

Ingår i Physics Letters B, s. 375-384, 2019.

#### Abstract

Using 16 energy points of e(+) e(-) annihilation data collected in the vicinity of the J/Psi resonance with the BESIII detector and with a total integrated luminosity of around 100 pb(-1), we study the relative phase between the strong and electromagnetic amplitudes of J/Psi decays. The relative phase between J/Psi electromagnetic decay and the continuum process (e(+) e(-) annihilation without the J/Psi resonance) is confirmed to be zero by studying the cross section lineshape of mu(+) mu(-) production. The relative phase between J/Psi strong and electromagnetic decays is then measured to be (84.9 +/- 3.6)degrees or (-84.7 +/- 3.1)degrees for the 2(pi(+) pi(-) )pi(0) final state by investigating the interference pattern between the J/Psi decay and the continuum process. This is the first measurement of the relative phase between J/Psi strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state eta pi(+) pi(-) with eta -> pi(+) pi(-) pi(0) , which provides additional information about the phase between the J/Psi electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of J/Psi -> 2(pi(+) pi(-) )pi(0) is measured to be (4.73 +/- 0.44)% or (4.85 +/- 0.45)%, and the branching fraction of J/Psi -> eta pi(+) pi(-) is measured to be (3.78 +/- 0.68) x 10(-4). Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.

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### Measurement of the branching fraction of J/psi -> omega eta 'pi(+)pi(-) and search for J/psi -> omega X(1835), X(1835) -> eta 'pi(+)pi(-) decay

Ingår i Physical Review D, 2019.

#### Abstract

Using a sample of 1.31 x 10(9) J/psi events collected by the BESIII detector at BEPCII during 2009 and 2012, we study the J/psi -> omega eta'pi(+)pi(-) thorn p-hadronic process. For the first time, we measure the branching ratio B(J/psi -> omega eta'pi(+)pi(-)) = (1.12 +/- 0.02 +/- 0.13) x 10(-3). We search for the X(1835) state in the eta'pi(+)pi(-) invariant mass spectra. No evidence is found and we estimate the upper limit on the branching fraction at 90% confidence level to be B(J/psi -> omega X(1835), X(1835) -> eta'pi(+)pi(-)) < 6.2 x 10(-5).

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of chi(cJ) -> 4K(S)(0)

Ingår i Physical Review D, 2019.

#### Abstract

By analyzing (448.1 +/- 2.9) x 10(6) psi(3686) events collected with the BESIII detector operating at the BEPCII collider, the decays of chi(c)(J) -> 4K(S)(0) (J = 0, 1, 2) are observed for the first time with statistical significances of 26.5 sigma, 5.9 sigma and 11.4 sigma, respectively. The product branching fractions of psi(3686) -> gamma chi(cJ), chi(cJ) -> 4K(S)(0 )are presented, and the branching fractions of chi(cJ) -> 4K(S)(0) decays are determined to be B-chi c0 -> 4KS0 = (5.76 +/- 0.34 +/- 0.38) x 10(-4), B-chi c1 -> 4KS0 = (0.35 +/- 0.09 +/- 0.03) x 10(-4) and B-chi c2 -> 4KS0( )= (1.14 +/- 0.15 +/- 0.08) x 10(-4), where the first uncertainties are statistical and the second are systematic, respectively.

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• Artikel i tidskrift

Haefner, G.; Moschner, K.; Blazhev, A.; Boutachkov, P. et al.

### Properties of γ-decaying Isomers in the 100Sn Region Revisited

Ingår i Acta Physica Polonica B, s. 431-437, 2019.

#### Abstract

The study of nuclei in the region around the N = Z doubly-magic nucleus 100Sn has been of long standing interest for the nuclear structure and nuclear astrophysics. Recently, Park et al.  have reported on properties of γ-decaying isomers and isomeric ratios in the vicinity of 100Sn. That experiment was performed at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center in Japan as a part of the EURICA campaign. Neutron-deficient nuclei were produced in a fragmentation reaction of a 124Xe primary beam on a 9Be target at an energy of 345 MeV/A. Secondary ions were separated and identified in the BigRIPS fragment separator and implanted in the silicon detector array WAS3ABi. The data presented here were obtained in another experiment performed at the RIBF using the same reaction but slightly different separator settings. New results of ratios of isomeric population and half-lives of γ-decaying isomers populated in the experiment are presented.

• Artikel i tidskrift

Jaworski, G.; Goasduff, A.; Canet, F. J. Egea; Modamio, V et al.

### The New Neutron Multiplicity Filter NEDA and Its First Physics Campaign with AGATA

Ingår i Acta Physica Polonica B, s. 585-590, 2019.

#### Abstract

A new neutron multiplicity filter NEDA, after a decade of design, R&D and construction, was employed in its first physics campaign with the AGATA spectrometer. Properties and performance of the array are discussed.

• Artikel i tidskrift

Valiente-Dobon, J. J.; Jaworski, G.; Goasduff, A.; Egea, J. et al.

### NEDA-NEutron Detector Array

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 81-86, 2019.

#### Abstract

The NEutron Detector Array, NEDA, will form the next generation neutron detection system that has been designed to be operated in conjunction with gamma-ray arrays, such as the tracking-array AGATA, to aid nuclear spectroscopy studies. NEDA has been designed to be a versatile device, with high-detection efficiency, excellent neutron-gamma discrimination, and high rate capabilities. It will be employed in physics campaigns in order to maximise the scientific output, making use of the different stable and radioactive ion beams available in Europe. The first implementation of the neutron detector array NEDA with AGATA 1 pi was realised at GANIL. This manuscript reviews the various aspects of NEDA.

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Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Search for baryon and lepton number violation in J/ψ → Λc+e- + c.c.

Ingår i Physical Review D, 2019.

#### Abstract

Using 1.31 x 109 J/ψ events collected by the BESIII detector at the Beijing Electron Positron Collider, we search for the process J/ψ → Λc+e- + c.c. for the first time. In this process, both baryon and lepton number conservation is violated. No signal is found and the upper limit on the branching fraction Β(J/ψ → Λc+e- + c.c.) is set to be 6.9 x 10-8 at the 90% confidence level.

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### First observations of h(c )-> hadrons

Ingår i Physical Review D, 2019.

#### Abstract

Based on (4.48 +/- 0.03) x 10(8) Psi(3686) events, collected with the BESIII detector at the BEPCII storage ring, five h(c) hadronic decays are searched for via the process Psi(3686) -> pi(0)h(c). Three of them, h(c) -> p (p) over bar pi(+)pi(-) , pi(+)pi(-)pi(0 )and 2(pi(+)pi(-))pi(0) are observed for the first time with significances of 7.4 sigma, 4.6 sigma, and 9.1 sigma, and their branching fractions are determined to be (2.89 +/- 0.32 +/- 0.55) x 10(-3), (1.60 +/- 0.40 +/- 0.32) x 10(-3), and (7.44 +/- 0.94 +/- 1.52) x 10(-3), respectively, where the first uncertainties are statistical and the second systematic. No significant signal is observed for the other two decay modes, and the corresponding upper limits of the branching fractions are determined to be B(h(c) -> 3(pi(+)pi(-))pi(0)) < 8.7 x 10(-3) and B(h(c) -> K+K-pi(+)pi(-) ) < 5.8 x 10(-4) at the 90% confidence level.

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• Artikel i tidskrift

### Cross section measurements of e(+) e(-) -> omega chi(c0) from root s=4.178 to 4.278 GeV

Ingår i Physical Review D, 2019.

#### Abstract

The cross section of the process e(+)e(-) -> omega chi(C0) is measured at center -of -mass energies from root s = 4.178 to 4.278 GeV using a data sample of 7 fb(-1) collected with the BESIII detector operating at the BEPCII storage ring. The dependence of the cross section on root s shows a resonant structure with mass of (4218.5 +/- 1.6(stat) +/- 4.0(syst)) MeV/c(2) and width of (28.2 +/- 3.9(stat) +/- 1.6(syst)) MeV, respectively. This observation confirms and improves upon the result of a previous study. The angular distribution of the e(+) e(-) ->omega chi(C0) process is extracted for the first time.

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• Artikel i tidskrift

### Study of the process e(+) e(-) -> p(p)over-bar via initial state radiation at BESIII

Ingår i Physical Review D, 2019.

#### Abstract

The Born cross section for the process e(+) e(-)-> p (p) over bar is measured using the initial state radiation technique with an undetected photon. This analysis is based on datasets corresponding to an integrated luminosity of 75 fb(-1), collected with the BESIII detector at the BEPCII collider at center of mass energies between 3.773 and 4.600 GeV. The Born cross section for the process e(+) e(-)-> p (p) over bar and the proton effective form factor are determined in the p (p) over bar invariant mass range between 2.0 and 3.8 GeV/c(2) divided into 30 intervals. The proton form factor ratio (vertical bar G(E)vertical bar/vertical bar G(M)vertical bar) is measured in 3 intervals of the p (p ) over bar invariant mass between 2.0 and 3.0 GeV/c(2).

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• Artikel i tidskrift

Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of the W-annihilation decay D-s(+) -> omega pi(+) and evidence for D-s(+) -> omega K+

Ingår i Physical Review D, 2019.

#### Abstract

We report the observation of W-annihilation decay D-s(+) -> omega pi(+) and evidence for D-s(+) -> omega K+ in a data sample corresponding to an integrated luminosity of 3.19 fb(-1) collected with the BESIII detector at a center-of-mass energy root s = 4.178 GeV. We obtain the branching fractions B(D-s(+) -> omega pi(+)) = (1.77 +/- 0.32(stat) +/- 0.13(sys)) x 10(-3) with a significance of 6.7 sigma and B(D-s(+) -> omega K+) = (0.87 +/- 0.24(stat) +/- 0.08(sys)) x 10(-3) with a significance of 4.4 sigma. This measurement provides critical information to determine the nonperturbative W-annihilation amplitudes and shows the potential of searching for CP asymmetry in D-s(+) -> omega K+.

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• Artikel i tidskrift

Akhunzyanov, R.; Alexeev, M. G.; Alexeev, G. D.; Amoroso, A. et al.

### Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section

Ingår i Physics Letters B, s. 188-194, 2019.

#### Abstract

We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/c polarised mu(+) and mu(-) beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured mu(+) and mu(-) cross sections for deeply virtual Compton scattering on the squared four-momentum transfer t from the initial to the final proton. The slope B of the t-dependence is fitted with a single exponential function, which yields B = (4.3 +/- 0.6(stat) (+0.1)(-0.3)vertical bar(sys)) (GeV/c)(-2). This result can be converted into a transverse extension of partons in the proton,root(r(perpendicular to)(2)) = (0.58 +/- 0.04(stat) (+0.01)(-0.02)vertical bar(sys) +/- 0.04(model)) fm. For this measurement, the average virtuality of the photon mediating the interaction is < Q(2)> = 1.8 (GeV/c)(2) and the average value of the Bjorken variable is < X-Bj > = 0.056.

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• Artikel i tidskrift

Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of the Decay X(3872) -> pi(0)chi(c1) (1P)

Ingår i Physical Review Letters, 2019.

#### Abstract

Using a total of 9.0 fb(-1) of e(+)e(-) collision data with center-of-mass energies between 4.15 and 4.30 GeV collected by the BESIII detector, we search for the processes e(+)e(-) gamma X(3872) with X(3872) -> pi(0)chi(cJ) for J = 0, 1, 2. We report the first observation of X(3872) -> pi(0)chi(c1), a new decay mode of the X(3872), with a statistical significance of more than 5 sigma for all systematic fit variations. Normalizing to the previously established process e(+)e(-) -> gamma X(3872) with X(3872) -> pi(+) pi(-) J/psi, we find B(X(3872) -> pi(0)chi(c1))/B(X(3872) -> pi+ pi(-) J/psi) = 0.88(-0.27)(+0.33) +/- 0.10, where the first error is statistical and the second is systematic. We set 90% confidence level upper limits on the corresponding ratios for the decays to pi(0)chi(c0) and pi(0)chi(c2) of 19 and 1.1, respectively.

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• Artikel i tidskrift

Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Search for heavy Majorana neutrino in lepton number violating decays of D -> K Π e(+)e(+)

Ingår i Physical Review D, 2019.

#### Abstract

Using a data sample with an integrated luminosity of 2.93 fb(-1) taken at the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino (nu(m)) in the lepton number violating decays D -> K pi e(+)e(+). No significant signal is observed, and the upper limits on the branching fraction at the 90% confidence level are set to be B(D degrees -> K-pi(-)e(+)e(+)) < 2.8 x 10(-6) , B(D+ -> K-S(0)pi(-) e(+)) < 3.3 x 10(-6) and B(D+ -> K-pi(0)e(+)e(+)) < 85 x 10(-6). The Majorana neutrino is searched for with different mass assumptions ranging from 0.25 to 1.0 GeV/c(2) in the decays D-0 -> K(-)e(+)nu(m),nu(m )-> pi(-)e(+) and D+ -> K(S)(0)e(+)nu(m),nu(m )->( )pi(-)e(+),and the upper limits on the branching fraction at the 90% confidence level are at the level of 10(-7) similar to 10(-6), depending on the mass of the Majorana neutrino. The constraints on the mixing matrix element vertical bar V-e nu m vertical bar(2) are also evaluated.

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• Artikel i tidskrift

Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Amplitude analysis and branching fraction measurement of D-0 -> K-pi(+)pi(0)pi(0)

Ingår i Physical Review D, 2019.

#### Abstract

Utilizing the dataset corresponding to an integrated luminosity of 2.93 fb(-1) at root s = 3.773 GeV collected by the BESIII detector, we report the first amplitude analysis and branching fraction measurement of the D-0 -> K- pi(+)pi(0)pi(0) decay. We investigate the substructures and determine the relative fractions and the phases among the different intermediate processes. Our results are used to provide an accurate detection efficiency and allow measurement of B(D-0 -> K- pi(+)pi(0)pi(0)) = (8.86 +/- 0.13(stat) +/- 0.19(syst))%.

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• Konferensbidrag

Li, Cui; Schönning, Karin

### Spin polarization of A hyperons in e(+)e(-) -> A(A)over-bar at BESIII

Ingår i XIII International Conference on Beauty, Charm and Hyperon Hadrons (BEACH 2018), 2019.

#### Abstract

The BESIII collaboration here reports the first observation of polarized A and A hyperons produced in two different processes: i) the resonant e+e AA, using a data sample of 1.31 x 109 J/ ti, events and ii) the non-resonant e+e 7* AA, using a 66.9 pb-1 data sample collected at \/7s = 2.396 GeV. In e+e J/ AA, the phase between the electric and the magnetic amplitude is measured for the first time to be 42.3' 0.6' 0.5'. The multi-dimensional analysis enables a model-independent measurement of the decay parameters for A (a_), A 257+ (a+) and A fi Tr (do). The obtained value a_ = 0.750 0.009 0.004 differs with 5a from the PDG value. This value, together with the measurement a+ = 0.758 0.010 0.007 allow for the most precise test of CP violation in A decays so far: Acp = (a_ + cx+)/(cx_ a+) of 0.006 0.012 0.007. The decay asymmetry Cxo = 0.692 0.016 0.006 is measured for the first time. The e+e AA reaction at 2.396 GeV enables a first complete measurement of the time-like electric and magnetic form factor of any baryon, of the modulus of the ratio R = IGEIGml and of the relative phase 0(13 = (DE (Dm. With the decay asymmetry parameters from the J/ data, the obtained values are R= 0.96 0.14 0.02 and,A(13 = 37- 12' 6'. In addition, the cross section has been measured with unprecedented precision to be a = 119.0 5.3 5.1 pb, which corresponds to an effective form factor of IQ = 0.123 0.003 0.003.

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• Konferensbidrag

### Lambda hyperon spin polarization and CP tests at BESIII

Ingår i MESON 2018 - 15th International Workshop on Meson Physics, 2019.

#### Abstract

In these proceedings two preliminary results from the BESIII collaboration on polarized Lambda and (Lambda) over bar are reported. Both results are first observations and concern the resonant and non-resonant processes e(-)e(+) -> J/psi -> Lambda(Lambda) over bar and e(-)e(+) -> gamma* -> Lambda Lambda at root s = 2.396 GeV, respectively. For J/psi -> Lambda Lambda the relative phase between the electric and magnetic form factors, Delta Phi, has for the first time been determined, Delta Phi = 42.4(6)(stat) (5)(stat degrees). That Delta Phi not equal 0 allows for a simultaneous measurement also of the asymmetry decay parameters Lambda -> p pi(-) (alpha_), (Lambda) over bar -> (p) over bar pi(+) (alpha(+)) and (Lambda) over bar -> (n) over bar pi(0) ((alpha) over bar (0)). The measured value of alpha_ = 0.750 +/- 0.009 +/- 0.004 differs by 17(3)% from the PDG value. The simultaneous measurement for the asymmetry parameters allows for the most precise test of CP violation conducted for A decays, A(cp) = - 0.006(12)(stat) (7)(syst). The reaction e(-)e(+) -> Lambda(Lambda) over bar at root s = 2.396 GeV is the first complete measurement of the time-like electric (G(E)) and magnetic (G(M)) form factor of any baryon as also the ratio R = vertical bar(GE)/(G(M))vertical bar and Delta Phi have been determined: R = 0.96(14)(12) and Delta Phi = 37(12)(stat) (6)(stat)degrees. The obtained cross-section and effective form factor are sigma = 119.0(53)(stat)(51)(syst) pb and vertical bar G vertical bar = 0.123 (3)(stat) (3)(syst), respectively.

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• Konferensbidrag

Pszczel, Damian; Stepaniak, J.

### Dielectron pairs from eta meson decays at WASA detector

Ingår i MESON 2018 - 15th International Workshop on Meson Physics, 2019.

#### Abstract

We present the results of the analysis of eta -> e(+)e(-)gamma and eta -> e(+)e(-) decays. The experimental data were collected in proton-proton collisions at incident proton kinetic energy 1.4 GeV using the WASA detector and the COSY storage ring. We describe the extraction procedure of the eta meson transition form factor, based on a sample of around 10(8)eta mesons, and show an attempt to search for physics beyond the Standard Model that led to the setting of an upper limit on the coupling between photons and hypothetical dark bosons. We also provide an estimate of the branching ratio upper limit for the very rare eta -> e(+)e(-) decay.

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• Konferensbidrag

Grzonka, D.; Alfs, D.; Asaturyan, A.; Carmignotto, M. et al.

### Polarization analysis of <(p)over bar> produced in pA collisions

Ingår i MESON 2018 - 15th International Workshop on Meson Physics, 2019.

#### Abstract

A quite simple procedure for the generation of a polarized antiproton beam could be worked out if antiprotons are produced with some polarization. In order to investigate this possibility measurements of the polarization of produced antiprotons have been started at a CERN/PS test beam. The polarization will be determined from the asymmetry of the elastic antiproton scattering at a liquid hydrogen target in the CNI region for which the analyzing power is well known. The data are under analysis and an additional measurement is done in 2018. Details on the experiment and the ongoing data analysis will be given.

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• Konferensbidrag

Alfs, D.; Asaturyan, A.; Carmignotto, M.; Diermaier, M. et al.

### Drift chamber calibration and particle identification in the P-349 experiment

Ingår i MESON 2018 - 15th International Workshop on Meson Physics, 2019.

#### Abstract

The goal of the P-349 experiment is to test whether 3.5 GeV/c antiprotons produced in high-energy proton-proton collisions are polarized in view of the preparation of a polarized antiproton beam. In this article, we present the details of the ongoing analysis focused on the drift chambers calibration and particle identification with DIRC.

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• Artikel i tidskrift

Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Observation and study of the decay J/psi -> phi eta eta '

Ingår i Physical Review D, 2019.

#### Abstract

We report the observation and study of the decay J/psi -> phi eta eta' phi eta eta' using 1.3 x 10(9) J/psi events collected with the BESIII detector. Its branching fraction, including all possible intermediate states, is measured to be (2.32 +/- 0.06 +/- 0.16) x 10(-4). We also report evidence for a structure, denoted as X, in the phi eta' mass spectrum in the 2.0-2.1 GeV/c(2) region. Using two decay modes of the eta' meson (gamma pi(+)pi(-) and eta pi(+)pi(-)), a simultaneous fit to the Ore mass spectra is performed. Assuming the quantum numbers of the X to be J(P) = 1(-), its significance is found to be 4.4 sigma, with a mass and width of (2002.1 +/- 27.5 +/- 21.4) MeV/c(2) and (129 +/- 17 +/- 9) MeV, respectively, and a product branching fraction B(J/psi -> eta X) x B(X -> phi eta') = (9.8 +/- 1.2 +/- 1.7) x 10(-5). Alternatively, assuming J(P) = 1(+), the significance is 3.8 sigma, with a mass and width of (2062.8 +/- 13.1 +/- 7.2) MeV/c(2) and (177 +/- 36 +/- 35) MeV, respectively, and a product branching fraction B(J/psi -> eta X)x B(X -> phi eta') = (9.6 +/- 1.4 +/- 2.0) x 10(-5). The angular distribution of J/psi -> eta X is studied and the two J(P) assumptions of the X cannot be clearly distinguished due to the limited statistics. In all measurements the first uncertainties are statistical and the second systematic.

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### Study of the decays D-s(+ )-> (KSK+)-K-0 and (KLK+)-K-0

Ingår i Physical Review D, 2019.

#### Abstract

Using an e(+)e(-) annihilation data sample corresponding to an integrated luminosity of 3.19 fb(-1) and collected at a center-of-mass energy root s = 4.178 GeV with the BESIII detector, we measure the absolute branching fractions B(D-s(+) -> (KSK+)-K-0) = (1.425 +/- 0.038(stat). +/- 0.031(syst).)% and B(D-s(+) -> (KLK+)-K-0) = (1.485 +/- 0.039(stat). +/- 0.046(syst).)%. The branching fraction of D-s(+) -> (KSK+)-K-0 is compatible with the world average and that of D-s(+) -> (KLK+)-K-0 is measured for the first time. We present the first measurement of the K-S(0)-K-L(0) asymmetry in the decays D-s(+) -> (KS,LK+)-K-0, and R((Ds+KS,LK+)-K-0) = B(D-s(+) -> (KSK+)-K-0)-B(D-s(+) -> (KLK+)-K-0)/B(D-s(+) -> (KSK+)-K-0)+B(D-s(+) -> (KLK+)-K-0) = (-2.1 +/- 1.9(stat). +/- 1.6(syst).)%. In addition, we measure the direct CP asymmetries A(CP) (D-s(+/-) -> (KSK +/-)-K-0). (0.6 +/- 2.8(stat). +/- 0.6(syst).)% and A(CP)(D-s(+/-) -> (KLK +/-)-K-0 ) = (-1.1 +/- 2.6(stat). +/- 0.6(syst))%.

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### Study of e(+)e(-) -> gamma omega J/psi and Observation of X(3872) -> omega J/psi

Ingår i Physical Review Letters, 2019.

#### Abstract

We study the e(+)e(-) -> gamma omega J/psi process using 11.6 fb(-1) e(+)e(-) annihilation data taken at center-of-mass energies from root s = 4.008 GeV to 4.600 GeV with the BESIII detector at the BEPCII storage ring. The X(3872) resonance is observed for the first time in the omega J/psi system with a significance of more than 5 sigma. The relative decay ratio of X(3872) -> omega J/psi and pi(+)pi(-)J/psi is measured to be R = 1.6(-0.3)(+0.4) +/- 0.2, where the first uncertainty is statistical and the second systematic (the same hereafter). The root s-dependent cross section of e(+)e(-) -> gamma X(3872) is also measured and investigated, and it can be described by a single Breit- Wigner resonance, referred to as the Y(4200), with a mass of 4200.6(-13.3)(+7.9) +/- 3.0 MeV/c(2) and a width of 115(-26)(+38) +/- 12 MeV. In addition, to describe the omega J/psi mass distribution above 3.9 GeV/c(2), we need at least one additional Breit-Wigner resonance, labeled as X(3915), in the fit. The mass and width of the X(3915) are determined. The resonant parameters of the X(3915) agree with those of the Y(3940) in B -> K omega J/psi and of the X(3915) in gamma gamma -> omega J/psi observed by the Belle and BABAR experiments within errors.

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Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Evidence for the decays of Lambda(+)(C) -> Sigma(+) eta and Sigma(+) eta '

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2019.

#### Abstract

We study the hadronic decays of Lambda(+)(C) to the final states Sigma(+) eta and Sigma(+) eta', using an e(+) e(-) annihilation data sample of 567 pb(-1) taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCII collider. We find evidence for the decays Lambda(+)(C) -> Sigma(+) eta and Sigma(+) eta' with statistical significance of and, respectively. Normalizing to the reference decays Lambda(+)(C) -> Sigma(+) pi(0) and Sigma(+) omega, we obtain the ratios of the branching fractions B(Lambda(+)(C) -> Sigma(+) eta)/B(Lambda(+)(C) -> Sigma(+) pi(0)) and B(Lambda(+)(C) -> Sigma(+) eta')/B(Lambda(+)(C) -> Sigma(+) omega) to be 0.35 +/- 0.16 +/- 0.02 and 0.86 +/- 0.34 +/- 0.04, respectively. The upper limits at the 90% confidence level are set to be B(Lambda(+)(C) -> Sigma(+) eta)/B(Lambda(+)(C) -> Sigma(+) pi(0)) < 0.58 and B(Lambda(+)(C) -> Sigma(+) eta')/B(Lambda(+)(C) -> Sigma(+) omega) < 1.2. Using BESIII measurements of the branching fractions of the reference decays, we determine B(Lambda(+)(C) -> Sigma(+) eta) = (0.41 +/- 0.19 +/- 0.05)% (<0.68%) and B(Lambda(+)(C) -> Sigma(+) eta') = (1.34 +/- 0.53 +/- 0.19)% (<1.9%). Here, the first uncertainties are statistical and the second systematic. The obtained branching fraction of Lambda(+)(C) -> Sigma(+) eta is consistent with the previous measurement, and the branching fraction of Lambda(+)(C) -> Sigma(+) eta' is measured for the first time.

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Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Polarization and entanglement in baryon-antibaryon pair production in electron-positron annihilation

Ingår i Nature Physics, s. 631-634, 2019.

#### Abstract

Particles directly produced at electron-positron colliders, such as the J/psi meson, decay with relatively high probability into a baryon-antibaryon pair(1). For spin-1/2 baryons, the pair can have the same or opposite helicites. A non-vanishing phase Delta Phi between the transition amplitudes to these helicity states results in a transverse polarization of the baryons(2-4). From the joint angular distribution of the decay products of the bary-ons, this phase as well as the parameters characterizing the baryon and the antibaryon decays can be determined. Here, we report the measurement of Delta Phi = 42.4 +/- 0.6 +/- 0.5 degrees using Lambda -> p pi(-) and (Lambda) over bar -> (p) over bar pi(+), (n ) over bar pi(0) decays at BESIII. We find a value for the Lambda -> p pi(-) decay parameter of alpha(-) = 0.750 +/- 0.009 +/- 0.004, 17 +/- 3% higher than the current world average, which has been used as input for all Lambda polarization measurements since 1978(5,6). For (Lambda) over bar -> (p) over bar pi(+) we find alpha(+) = -0.758 +/- 0.010 +/- 0.007, giving A(CP) = (alpha(-) + alpha(+))/(alpha(-) - alpha(+)) = -0.006 +/- 0.012 +/- 0.007, a precise direct test of charge-parity symmetry (CP) violation in Lambda decays.

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### Observation of psi(3686) -> p(p)over-bar phi

Ingår i Physical Review D, 2019.

#### Abstract

Using a data sample of 4.48 x 10(8) psi(3686) events collected with the BESIII detector, we present a first observation of psi(3686) -> p (p) over bar phi, and we measure its branching fraction to be [6.06 +/- 0.38(stat)+/- 0.48(syst)] x 10(-6). In contrast to the earlier discovery of a threshold enhancement in the p (p) over bar -mass spectrum of the channel j/psi -> gamma p (p) over bar, denoted as X(p (p) over bar), we do not find a similar enhancement in psi(3686) -> p (p) over bar phi. An upper limit of 1.82 x 10(-7) at the 90% confidence level on the branching fraction of psi(3686) -> X(p (p) over bar)phi -> p (p) over bar phi is obtained.

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Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Measurements of the branching fractions of eta(c) -> K+ K- pi(0), (KSK +/-)-K-0 pi(-/+), 2(pi(+) pi(-) pi(0)), and p(p)over-bar

Ingår i Physical Review D, 2019.

#### Abstract

Using data samples collected with the BESIII detector at center-of-mass energies root s = 4.23, 4.26, 4.36, and 4.42 GeV, we measure the branching fractions of eta(c) -> K+ K- pi(0), (KSK +/-)-K-0 pi(-/+), 2(pi(+) pi(-) pi(0)), and p (p) over bar, via the process e(+) e(-) -> pi(+) pi(-) h(c), h(c) -> gamma eta(c). The corresponding results are (1.15 +/- 0.12 +/- 0.10)%, (2.60 +/- 0.21 +/- 0.20)%, (15.2 +/- 1.8 +/- 1.7)%, and (0.120 +/- 0.026 +/- 0.015)%, respectively. Here the first uncertainties are statistical, and the second ones systematic. Additionally, the charged track multiplicity of eta(c) decays is measured for the first time.

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### Observation of e(+)e(-) -> pi(+) pi(-)psi(3770) and D-1(2420)(0)(D)over-bar(0) + c.c

Ingår i Physical Review D, 2019.

#### Abstract

Several intermediate states of the reaction channels e(+)e(-) -> pi(+)pi(-) D-0(D) over bar (0) and e(+)e(-) -> pi(+)pi-D+D- are studied using the data samples collected with the BESIII detector at center-of-mass energies above 4.08 GeV. For the first time in this final state, a psi(3770) signal is seen in the DD invariant mass spectrum, with a statistical significance of 5.2 sigma at root s = 4.42 GeV. There is also evidence for this resonance at root s = 4.26 and 4.36 GeV with statistical significance of 3.2 sigma and 3.3 sigma, respectively. In addition, the Born cross section of e(+)e(-) ->pi(+)pi(-)psi(3770) is measured. The proposed heavy-quark-spin-symmetry partner of the X(3872), the state X-2(4013), is also searched for in the D (D) over bar invariant mass spectra. No obvious signal is found. The upper limit of the Born cross section of the process e(+)e(-) -> rho X-0(2)(4013) combined with the branching fraction is measured. Also, the processes e(+)e(-) -> D-1(2420)(D) over bar c.c. are investigated. The neutral mode with D-1(2420)(0) -> D-0 pi(+)pi(-) is reported with statistical significance of 7.4 sigma at root s = 4.42 GeV for the first time, and evidence with statistical significance of 3.2 sigma and 3.3 sigma at root s = 4.36 and 4.60 GeV is seen, respectively. No evident signal for the process e(+)e(-) -> D-1(2420)(0)(D) over bar (0) + c.c., D-1(2420)(0) -> D*(+)pi(-) is reported. Evidence for e(+)e(-) -> D-1(2420)+D- + c.c., D-1(2420)(+) -> D+pi(+)pi(-) is reported with statistical significance of 3.1 sigma and 3.0 sigma at root s. = 4.36 and 4.42 GeV, respectively.

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Ekstedt, Andreas; Ghaderi, Hazhar; Ingelman, Gunnar; Leupold, Stefan

### Nucleon parton distributions from hadronic quantum fluctuations

Ingår i Physical Review D, 2019.

#### Abstract

A physical model is presented for the nonperturbative parton distributions in the nucleon. This is based on quantum fluctuations of the nucleon into baryon-meson pairs convoluted with Gaussian momentum distributions of partons in hadrons. The hadronic fluctuations, here developed in terms of hadronic chiral perturbation theory, occur with high probability and generate sea quarks as well as dynamical effects also for valence quarks and gluons. The resulting parton momentum distributions f(x,Q20) at low momentum transfers are evolved with conventional Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equations from perturbative QCD to larger scales. This provides parton density functions f(x,Q2) for the gluon and all quark flavors with only five physics-motivated parameters. By tuning these parameters, experimental data on deep-inelastic structure functions can be reproduced and interpreted. The contribution to sea quarks from hadronic fluctuations explains the observed asymmetry between ¯u and ¯d in the proton. The strange-quark sea is strongly suppressed at low Q2, as observed.

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Haefner, G.; Moschner, K.; Blazhev, A.; Boutachkov, P. et al.

### Properties of gamma-decaying isomers in the Sn-100 region populated in fragmentation of a Xe-124 beam

Ingår i Physical Review C, 2019.

#### Abstract

A systematic study was performed of microsecond gamma-decaying isomers around Sn-100 produced in a fragmentation reaction of a Xe-124 beam at 345 MeV/u at the Radioactive Ion Beam Factory of the RIKEN Nishina Center in Saitama, Japan. Half-lives of isomeric states in that region were remeasured allowing us to improve the currently available experimental information. Reduced transition probabilities were deduced and compared to shell-model calculations in various model spaces. The recently reported low-energy transitions in Rh-92 and Ag-96 were remeasured with improved precision. Additionally, experimental information on isomeric ratios, including five new ones, were extracted and compared to a previous experimental study and the sharp cutoff model of fragmentation reaction.

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### Partial-wave analysis of J/psi -> K+ K- pi(0)

Ingår i Physical Review D, 2019.

#### Abstract

A partial-wave analysis of the decay J/psi -> K+ K- pi(0) has been made using (223.7 +/- 1.4) x 10(6) J/psi events collected with the BESIII detector in 2009. The analysis, which is performed within the isobar-model approach, reveals contributions from K-2* (1430)(+/-), K-2* (1980)(+/-) and K-4* (2045)(+/-) decaying to K-+/-pi(0). The two latter states are observed in J/psi decays for the first time. Two resonance signals decaying to K+ K- are also observed. These contributions cannot be reliably identified and their possible interpretations are discussed. The measured branching fraction B(J/psi -> K+ K- pi(0)) of (2.88 +/- 0.01 +/- 0.12) x 10(-3) is more precise than previous results. Branching fractions for the reported contributions are presented as well. The results of the partial-wave analysis differ significantly from those previously obtained by BESII and BABAR.

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### Cross section measurements of e+e- -> K+ K- K+ K- and ΦK+ K- at center-of-mass energies from 2.10 to 3.08 GeV

Ingår i Physical Review D, 2019.

#### Abstract

We measure the Born cross sections of the process e(+)e(-) -> K+ K- K+ K- at center-of-mass (c.m.) energies, root s, between 2.100 and 3.080 GeV. The data were collected using the BESIII detector at the BEPCII collider. An enhancement at root s = 2.232 GeV is observed, very close to the e(+)e(-) -> Lambda(Lambda) over bar production threshold. A similar enhancement at the same c.m. energy is observed in the e(+)e(-) -> phi K+ K- cross section. The energy dependence of the K+ K- K+ K- and phi K+ K- cross sections differs significantly from that of e(+)e(-) -> phi pi(+)pi(-).

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Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Amplitude Analysis of D-s(+) -> pi(+)pi(0)eta and First Observation of the W-Annihilation Dominant Decays D-s(+) -> a(0)(980)(+)pi(0) and D-s(+) -> a(0)(980)(0)pi(+)

Ingår i Physical Review Letters, 2019.

#### Abstract

We present the first amplitude analysis of the decay D-s(+) -> pi(+)pi(0)eta. We use an e(+)e(-) collision data sample corresponding to an integrated luminosity of 3.19 fb(-1) collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. We observe for the first time the W-annihilation dominant decays D-s(+) -> a(0)(980)(+)pi(0) and D-s(+) -> a(0)(980)(0)pi(+). We measure the absolute branching fraction B(D-s(+) -> a(0)(980)(+(0))pi(0(+)), a(0)(980)(+(0)) -> pi(+(0)())eta = (1.46 +/- 0.15(stat )+/- 0.23 sys)%, which is larger than the branching fractions of other measured pure W-annihilation decays by at least one order of magnitude. In addition, we measure the branching fraction of D-s(+) -> pi(+)pi(0)eta with significantly improved precision.

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### Search for the decay eta ' -> gamma gamma eta (Search for the decay η′→γγη)

Ingår i Physical Review D, 2019.

#### Abstract

Using a data sample of 1.31 x 10(9) J/psi events collected with the BESIII detector, a search for eta' -> gamma gamma eta via J/psi ->gamma eta' is performed for the first time. No significant eta' signal is observed in the gamma gamma eta invariant mass spectrum, and the branching fraction of eta' -> gamma gamma eta is determined to be less than 1.33 x 10(-4) at the 90% confidence level.

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Ablikim, M.; Ikegami Andersson, Walter; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of eta(c) -> omega omega in J/psi -> gamma omega omega

Ingår i Physical Review D, 2019.

#### Abstract

Using a sample of (1310.6 +/- 7.0) x 10(6) J/psi events recorded with the Beijing Spectrometer III detector at the Beijing Electron Positron Collider II, we report the observation of the decay of the (1(1)S(0)) charmonium state eta(c) into a pair of omega mesons in the process J/psi -> gamma omega omega. The branching fraction is measured for the first time to be B(eta(c) -> omega omega) = (2.88 +/- 0.10 +/- 0.46 +/- 0.68) x 10(-3), where the first uncertainty is statistical, the second systematic, and the third is from the uncertainty of B(J/psi -> gamma eta(c)). The mass and width of the eta(c) are determined as M = (2985.9 +/- 0.7 +/- 2.1) MeV/c(2) and Gamma = (33.8 +/- 1.6 +/- 4.1) MeV.

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Ralet, D.; Clement, E.; Georgiev, G.; Stuchbery, A. E. et al.

### Evidence of octupole-phonons at high spin in Pb-207

Ingår i Physics Letters B, 2019.

#### Abstract

A lifetime measurement of the 19/2(-) state in Pb-207 has been performed using the Recoil Distance Doppler-Shift (RDDS) method. The nuclei of interest were produced in multi-nucleon transfer reactions induced by a Pb-208 beam impinging on a Mo-100 enriched target. The beam-like nuclei were detected<bold> </bold>and identified in terms of their atomic mass number in the VAMOS++ spectrometer while the prompt gamma rays were detected by the AGATA tracking array. The measured large reduced transition probability B(E3, 19/2(-) -> 13/2(+)) = 40(8) W.u. is the first indication of the octupole phonon at high spin in Pb-207. An analysis in terms of a particle-octupole-vibration coupling model indicates that the measured B(E3) value in Pb-207 is compatible with the contributions from single-phonon and single particle E3 as well as E3 strength arising from the double-octupole-phonon 6(+) state, all adding coherently. A crucial aspect of the coupling model, namely the strong mixing between single-hole and the phonon-hole states, is confirmed in a realistic shell-model calculation. Crown Copyright (C) 2019 Published by Elsevier B.V.<bold> </bold>

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Boso, A.; Milne, S. A.; Bentley, M. A.; Recchia, F. et al.

### Isospin dependence of electromagnetic transition strengths among an isobaric triplet

Ingår i Physics Letters B, 2019.

#### Abstract

Electric quadrupole matrix elements, M-p, for the J(pi) = 2(+) -> 0(+), Delta T = 0, T = 1 transitions across the A = 46 isobaric multiplet Cr-46-V-46-Ti-46 have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows direct insight into the isospin purity of the states of interest by testing the linearity of M-p with respect to T-z. Pairs of nuclei in the T = 1 triplet were studied using identical reaction mechanisms in order to control systematic errors. The M-p values were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for Cr-46 and Ti-46; (ii) a "stretched target" technique was adopted here, for the first time, for lifetime measurements in V-46 and Ti-46. A constant value of M-p across the triplet has been observed. Shell-model calculations performed within the fp shell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sd shell. A test of the linearity rule for all published data on complete T = 1 isospin triplets is presented. (C) 2019 The Author(s). Published by Elsevier B.V.

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### Complete Measurement of the Λ Electromagnetic Form Factors

Ingår i Physical Review Letters, 2019.

#### Abstract

The exclusive process e(+)e(-) -> Lambda(Lambda) over bar, with Lambda -> p pi(-) and (Lambda) over bar -> (p) over bar pi(+), has been studied at root s = 2.396 GeV for measurement of the timelike Lambda electric and magnetic form factors, G(E) and G(M). A data sample, corresponding to an integrated luminosity of 66.9 pb(-1), was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R = vertical bar G(E)/G(M)vertical bar and, for the first time for any baryon, the relative phase Delta Phi = Phi(E) - Phi(M). The resulting values are R = 0.96 +/- 0.14(stat) +/- 0.02(syst) and Phi(F) = 37 degrees +/- 12 degrees (stat) +/- 6 degrees (syst), respectively. These are obtained using the recently established and most precise value of the asymmetry parameter alpha(Lambda) = 0.750 +/- 0.010 measured by BESIII. In addition, the cross section is measured with unprecedented precision to be sigma = 118.7 +/- 5.3(stat) +/- 5.1(syst) pb, which corresponds to an effective form factor of vertical bar G vertical bar = 0.123 +/- 0.003(stat) +/- 0.003(syst). The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.

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### Observation of psi(3886) -> Xi(1530)(-)(Xi)over-bar(1530)(+) and Xi(1530)(-)(Xi)over-bar(+)

Ingår i Physical Review D, 2019.

#### Abstract

Using 448.1 x 10(6) psi(3686) events collected with the BESIII detector at BEPCII, we employ a single-baryon tagging technique to make the first observation of psi(3686) -> Xi(1530)(-)(Xi) over bar (1530)(+) and Xi(1530)(-)(Xi) over bar (+) decays with a statistical significance of more than 10 sigma and 5.0 sigma, respectively. The branching fractions are measured to be B(psi(3686) -> Xi(1530)(-)(Xi) over bar (1530)(+)) = (11.45 +/- 0.40 +/- 0.59) x 10(-5) and B(psi(3686) -> Xi(1530)(-)(Xi) over bar (+)) = (0.70 +/- 0.11 +/- 0.04) x 10(-5). The angular distribution parameter for psi(3686) -> Xi(1530)(-)(Xi) over bar (1530)(+) is determined to be alpha = 0.40 +/- 0.24 +/- 0.06, which agrees with the theoretical predictions within 1 sigma. The first uncertainties are statistical, and the second systematic.

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### Study of the decays psi(3686) -> gamma chi(cJ) -> gamma(p)over-barK*(+)Lambda + c.c. and psi(3686) -> (p)over-barK*(+) Lambda plus c.c.

Ingår i Physical Review D, 2019.

#### Abstract

Based on the data sample of 448.1 x 10(6) psi(3686) events collected with the BESIII detector at BEPCII, we present a study of the decays psi(3686) -> gamma chi(cJ) -> gamma(p) over barK*(+)Lambda + c.c. and psi(3686) -> (p) over barK*(+)Lambda + c.c. The branching fractions of chi(cJ )-> (p) over barK*(+)Lambda + c.c. (J = 0, 1, 2) are measured to be (4.8 +/- 0.7 +/- 0.5) x 10(-4), (5.0 +/- 0.5 +/- 0.4) x 10(-4), and (8.2 +/- 0.9 +/- 0.7) x 10(-4), respectively, where the first uncertainties are statistical and the second systematic. The branching fraction of psi(3686) -> (p) over barK*(+)Lambda + c.c. is measured to be (6.3 +/- 0.5 +/- 0.5) x 10(-5). All these decay modes are observed for the first time.

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### Measurements of weak decay asymmetries of Lambda(+)(c) -> pK(S)(0), Lambda pi(+), Sigma(+)pi(0), and Sigma(0)pi(+)

Ingår i Physical Review D, 2019.

#### Abstract

Using e(+)e(-) -> Lambda(+)(c)(Lambda) over bar (-)(c). production from a 567 pb(-1) data sample collected by BESIII at 4.6 GeV, a full angular analysis is carried out simultaneously on the four decay modes of Lambda(+)(c) -> pK(S)(0), Lambda pi(+), Sigma(+)pi(0), and Sigma(0)pi(+). For the first time, the Lambda(+)(c) transverse polarization is studied in unpolarized e(+)e(-) collisions, where a nonzero effect is observed with a statistical significance of 2.1 sigma. The decay asymmetry parameters of the Lambda(+)(c) weak hadronic decays into pK(S)(0), Lambda pi(+), Sigma(+)pi(0), and Sigma(0)pi(+) are measured to be 0.18 +/- 0.43(stat) +/- 0.14(syst), -0.80 +/- 0.11(stat) +/- 0.02(syst), -0.57 +/- 0.10(stat) +/- 0.07(syst), and -0.73 +/- 0.17(stat) +/- 0.07(syst), respectively. In comparison with previous results, the measurements for the Lambda pi(+) and Sigma(+)pi(0) modes are consistent but with improved precision, while the parameters for the pK(S)(0) and Sigma(+)pi(0) modes are measured for the first time.

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### Improved measurements of the absolute branching fractions of the inclusive decays D+(0) -> phi X

Ingår i Physical Review D, 2019.

#### Abstract

By analyzing 2.93 fb(-1) of e(+)e(-) annihilation data taken at the center-of-mass energy root s = 3.773 GeV with the BESIII detector, we determine the branching fractions of the inclusive decays D+-> phi X and D-0 -> phi X to be (1.135 +/- 0.034 +/- 0.031)% and (1.091 +/- 0.027 +/- 0.035)%, respectively, where X denotes any possible particle combination. The first uncertainties are statistical, and the second are systematic. We also determine the branching fractions of the decays D -> phi X and their charge conjugate modes (D) over bar -> phi(X) over bar separately for the first time, and no significant CP asymmetry is observed.

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### Amplitude analysis of D+-> K-S(0)pi(+)pi(+)pi(-)

Ingår i Physical Review D, 2019.

#### Abstract

The decay D+-> K-S(0)pi(+)pi(+)pi(-) is studied with an amplitude analysis using a data set of 2.93 fb(-1) of e(+)e(-) collisions at the psi(3770) peak accumulated by the BESIII detector. Intermediate states and nonresonant components, and their relative fractions and phases, have been determined. The significant amplitudes, which contribute to the model that best fits the data, are composed of five quasitwo-body decays K(S)(0)a(1)(1260)(+), (K) over bar (1)(1270)(0)pi(+) (K) over bar (1)(1400)(0)pi(+), (K) over bar (1)(1650)(0)pi(+), and (K) over bar (1460)(0)pi(+), a three-body decay K-S(0)pi(+)rho(0), as well as a nonresonant component K-S(0)pi(+)pi(+)pi(-). The dominant amplitude is K(S)(0)a(1)(1260)(+), with a fit fraction of (40.3 +/- 2.1 +/- 2.9)%, where the first and second uncertainties are statistical and systematic, respectively.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of the matrix elements for the decays eta' -> eta pi(+) pi(-) and eta' -> eta pi(0)pi(0)

Ingår i Physical Review D, 2018.

#### Abstract

Based on a sample of 1.31 x 10(9) J/psi events collected with the BESIII detector, the matrix elements for the decays eta' -> eta pi(+) pi(-) and eta' -> eta pi(0)pi(0) are determined using 351,016 eta' -> (eta -> gamma gamma)pi' pi(-) and 56,249 eta' -> (eta -> gamma gamma)pi(0) pi(0) events with background levels less than 1%. Two commonly used representations are used to describe the Dalitz plot density. We find that an assumption of a linear amplitude does not describe the data well. A small deviation of the obtained matrix elements between eta' -> eta pi(+) pi(-) and eta' -> eta pi(0)pi(0) is probably caused by the mass difference between charged and neutral pions or radiative corrections. No cusp structure in eta' -> eta pi(0)pi(0) is observed.

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Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Spin Dependence of eta Meson Production in Proton-Proton Collisions Close to Threshold

Ingår i Physical Review Letters, 2018.

#### Abstract

Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high polarization degree of the proton beam of COSY, the reaction →pp→ppη has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than 1 order of magnitude with respect to previous results, allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q=15  MeV, signaling s-wave production with no evidence for higher partial waves. At Q=72  MeV the data reveal strong interference of Ps and Pp partial waves and cancellation of (Pp)2 and Ss∗Sd contributions. These results rule out the presently available theoretical predictions for the production mechanism of the η meson.

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Leupold, Stefan

### The nucleon as a test case to calculate vector-isovector form factors at low energies

Ingår i European Physical Journal A, 2018.

#### Abstract

Extending a recent suggestion for hyperon form factors to the nucleon case, dispersion theory is used to relate the low-energy vector-isovector form factors of the nucleon to the pion vector form factor. The additionally required input, i.e. the pion-nucleon scattering amplitudes are determined from relativistic next-to-leading-order (NLO) baryon chiral perturbation theory including the nucleons and optionally the Delta baryons. Two methods to include pion rescattering are compared: a) solving the Muskhelishvili-OmnSs (MO) equation and b) using an N/D approach. It turns out that the results differ strongly from each other. Furthermore the results are compared to a fully dispersive calculation of the (subthreshold) pion-nucleon amplitudes based on Roy-Steiner (RS) equations. In full agreement with the findings from the hyperon sector it turns out that the inclusion of Delta baryons is not an option but a necessity to obtain reasonable results. The magnetic isovector form factor depends strongly on a low-energy constant of the NLO Lagrangian. If it is adjusted such that the corresponding magnetic radius is reproduced, then the results for the corresponding pion-nucleon scattering amplitude (based on the MO equation) agree very well with the RS results. Also in the electric sector the Delta degrees of freedom are needed to obtain the correct order of magnitude for the isovector charge and the corresponding electric radius. Yet quantitative agreement is not achieved. If the subtraction constant that appears in the solution of the MO equation is not taken from nucleon+Delta chiral perturbation theory but adjusted such that the electric radius is reproduced, then one obtains also in this sector a pion-nucleon scattering amplitude that agrees well with the RS results.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurements of the branching fractions for the semileptonic decays D-s(+) -> phi e(+)v(e), phi mu(+)v(mu), eta mu(+)v(mu) and eta 'mu(+)v(mu)

Ingår i Physical Review D, 2018.

#### Abstract

By analyzing 482 pb(-1) of e(+) e(-) collision data collected at the center-of-mass energy root s = 4.009 GeV with the BESIII detector, we measure the branching fractions for the semi-leptonic decays D-s(+) -> phi e(+)v(e), phi mu(+)v(mu), eta mu(+)v(mu) and eta'mu(+)v(mu) to be B(D-s(+) -> phi e(+)v(e)) = (2.26 +/- 0.45 +/- 0.09)%, B(D-s(+) -> phi mu+v(mu)) = (1.94 +/- 0.53 +/- 0.09)%, B(D-s(+) -> eta mu(+)v(mu)) = (2.42 +/- 0.46 +/- 011)% and B(D-s(+) -> eta'mu(+)v(mu)) = (1.06 +/- 0.54 +/- 0.07)%, where the first and second uncertainties are statistical and systematic, respectively. The branching fractions for the three semi-muonic decays D-s(+) -> phi mu(+)v(mu), eta mu(+)v(mu) and eta'mu(+)v(mu) are determined for the first time and that of D-s(+) -> phi e(+)v(e) is consistent with the world average value within uncertainties.

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Fäldt, Göran; Wilkin, C.

### Phenomenological study of the pp -> pi(+) pn reaction

Ingår i Physical Review C, 2018.

#### Abstract

Fully constrained bubble chamber data on the pp -> pi(+) pn and pp -> pi(+) d reactions are used to investigate the ratio of the counting rates for the two processes as function of the pn excitation energy Q. Though it is important to include effects associated with the p-wave nature of pion production, the data are insufficient to establish unambiguously the dependence on Q. The angular distributions show the presence of higher partial waves which seem to be anomalously large at small Q. The dispersion relation method to determine scattering lengths is extended to encompass cases where, as for the pp -> pi(+) pn reaction, there is a bound state and, in a test example, it is shown that the values deduced for the low-energy neutron-proton scattering parameters are significantly influenced by the pion p-wave behavior.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Observation of e(+)e(-) -> phi chi(c1) and phi chi(c2) at root s=4.600 GeV

Ingår i Physical Review D, 2018.

#### Abstract

Using a data sample collected with the BESIII detector operating at the BEPCII storage ring at a center-of-mass energy of root s = 4.600 GeV, we search for the production of e(+)e(-) -> phi chi(c0,1,2). A search is also performed for the charmonium-like state X(4140) in the radiative transition e(+)e(-) -> gamma X(4140) with X(4140) subsequently decaying into phi J/psi The processes e(+)e(-) -> phi chi(c1) and phi chi(c2) are observed for the first time, each with a statistical significance of more than 10 sigma, and the Born cross sections are measured to be (4.2(-1.0)(+1.7) +/- 0.3) and (6.7(-1.7)(+3.4) +/- 0.5) pb, respectively, where the first uncertainties are statistical and the second systematic. No significant signals are observed for e(+)e(-) -> phi chi(c0) and e(+)e(-) -> gamma X(4140) and upper limits on the Born cross sections at 90% C. L. are provided at root s = 4.600 GeV.

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Aghasyan, M.; Alexeev, M. G.; Alexeev, G. D.; Amoroso, A. et al.

### Transverse-momentum-dependent multiplicities of charged hadrons in muon-deuteron deep inelastic scattering

Ingår i Physical Review D, 2018.

#### Abstract

A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality Q(2) > 1 (GeV/c)(2), invariant mass of the hadronic system W > 5 (GeV/c)(2), Bjorken scaling variable in the range 0.003 < x < 0.4, fraction of the virtual photon energy carried by the hadron in the range 0.2 < z < 0.8, and square of the hadron transverse momentum with respect to the virtual photon direction in the range 0.02 (GeV/c)(2) < P-hT(2) < 3 (GeV/c)(2). The multiplicities are presented as a function of P-hT(2) in three-dimensional bins of x, Q(2), z and compared to previous semi-inclusive measurements. We explore the small-P-hT(2) region, i.e. P-hT(2) < 1 (GeV/c)(2), where hadron transverse momenta are expected to arise from nonperturbative effects, and also the domain of larger P-hT(2), where contributions from higher-order perturbative QCD are expected to dominate. The multiplicities are fitted using a single-exponential function at small P-hT(2) to study the dependence of the average transverse momentum < P-hT(2)> on x, Q(2) and z. The power-law behavior of the multiplicities at large P-hT(2) is investigated using various functional forms. The fits describe the data reasonably well over the full measured range.

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Hadynska-Klek, K.; Napiorkowski, P. J.; Zielinska, M.; Srebrny, J. et al.

### Quadrupole collectivity in Ca-42 from low-energy Coulomb excitation with AGATA

Ingår i Physical Review C, 2018.

#### Abstract

ACoulomb-excitation experiment to study electromagnetic properties of Ca-42 was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. gamma rays from excited states in Ca-42 were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2 matrix elements coupling six low-lying states in Ca-42, including the diagonal E2 matrix elements of 2(1)(+) and 2(2)(+) states, were determined using the least-squares code GOSIA. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 0(1),(+)(2) and 2(1,2)(+) states, as well as triaxiality for 0(1,2)(+) states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca-42. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in Ca-42.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Observation of a cross-section enhancement near mass threshold in e(+)e(-) -> Lambda(Lambda)over-bar

Ingår i Physical Review D, 2018.

#### Abstract

The process e(+)e(-) -> Lambda(Lambda) over bar is studied using data samples at root s = 2.2324, 2.400, 2.800 and 3.080 GeV collected with the BESIII detector operating at the BEPCII collider. The Born cross section is measured at root s = 2.2324 GeV, which is 1.0 MeVabove the Lambda(Lambda) over bar mass threshold, to be 305 +/- 45(-36)(+66) pb, where the first uncertainty is statistical and the second systematic. The cross section near threshold is larger than that expected from theory, which predicts the cross section to vanish at threshold. The Born cross sections at root s = 2.400, 2.800 and 3.080 GeV are measured and found to be consistent with previous experimental results, but with improved precision. Finally, the corresponding effective electromagnetic form factors of Lambda are deduced.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of e+e−→π0π0ψ(3686) at √s from 4.009 to 4.600 GeV and observation of a neutral charmoniumlike structure

Ingår i Physical Review D, 2018.

#### Abstract

Using ethorne-collision data collected with the BESIII detector at the BEPCII collider corresponding to an integrated luminosity of 5.2 fb(-1) at center-of-mass energies (root s) from 4.009 to 4.600 GeV, the process e(+)e(-) -> pi(0)pi(0)psi(3686) is studied for the first time. The corresponding Born cross sections are measured and found to be half of those of the reaction e(+)e(-) -> pi(0)pi(0)psi(3686). This is consistent with the expectation from isospin symmetry. Furthermore, the Dalitz plots for pi(0)pi(0)psi(3686) are accordant with those of pi(0)pi(0)psi(3686) at all energy points, and a neutral analog to the structure in pi(+/-)psi(3686) around 4040 MeV/c(2) first observed at root s = 4.416 GeV is observed in the isospin neutral mode at the same energy.

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Fäldt, Göran

### Production and sequential decay of charmed hyperons

Ingår i Physical Review D, 2018.

#### Abstract

We investigate production and decay of the Lambda(+)(c) thornc hyperon. The production considered is through the e(+)e(-) annihilation channel, e(+)e(-) -> Lambda(+)(c)(Lambda) over bar (-)(c), with summation over the (Lambda) over bar (-)(c) antihyperon spin directions. It is in this situation that the Lambda(+)(c) decay chain is identified. Two kinds of sequential decays are studied. The first one is the doubly weak decay B-1 -> B2M2, followed by B-2 -> B3M3. The other one is the mixed weak-electromagnetic decay B-1 -> B2M2, followed by B-2 -> B-3 gamma. In both schemes B denotes baryons and M mesons. We should also mention that the initial state of the Lambda(+)(c) thornc hyperon is polarized.

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Leupold, Stefan; Hoferichter, Martin; Kubis, Bastian; Niecknig, Franz et al.

### Towards a dispersive determination of the pion transition form factor

Ingår i EPJ Web of Conferences, 2018.

#### Abstract

We start with a brief motivation why the pion transition form factor is interesting and, in particular, how it is related to the high-precision standard-model calculation of the gyromagnetic ratio of the muon. Then we report on the current status of our ongoing project to calculate the pion transition form factor using dispersion theory. Finally we present and discuss a wish list of experimental data that would help to improve the input for our calculations and/or to cross-check our results.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albayrak, O. et al.

### Study of eta(1475) and X(1835) in radiative J/psi decays to gamma phi

Ingår i Physical Review D, 2018.

#### Abstract

The decay J/psi -> gamma gamma phi is studied using a sample of 1.31 x 10(9) J/psi events collected with the BESIII detector. Two structures around 1475 MeV/c(2) and 1835 MeV/c(2) are observed in the gamma phi invariant mass spectrum for the first time. With a fit on the gamma phi invariant mass, which takes into account the interference between the two structures, and a simple analysis of the angular distribution, the structure around 1475 MeV/c(2) is found to favor an assignment as the eta(1475) and the mass and width for the structure around 1835 MeV/c(2) are consistent with the X(1835). The statistical significances of the two structures are 13.5 sigma and 6.3 sigma, respectively. The results indicate that both eta(1475) and X(1835) contain a sizeable s (s) over bar component.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albayrak, O. et al.

### Measurements of the branching fractions of the singly Cabibbo-suppressed decays D0→ωη, η(')π0 and η(')η

Ingår i Physical Review D, 2018.

#### Abstract

By analyzing a data sample of 2.93 fb(-1) collected at root s = 3.773 GeV with the BESIII detector operated at the BEPCII storage rings, we measure the branching fractions B(D-0 -> omega eta) = (2.15 +/- 0.17(stat) +/- 0.15(sys)) x 10(-3), B(D-0 ->eta pi(0)) = (0.58 +/- 0.05(stat) +/- 0.05(sys)) x 10(-3), B(D-0 ->eta'pi(0)) = (0.93 +/- 0.11(stat) +/- 0.09(sys)) x 10(-3), B(D-0 -> eta eta) = (2.20 +/- 0.07(stat) +/- 0.06(sys)) x 10(-3) and B(D-0 -> eta'eta) = (0.94 degrees +/- 0.25(stat) +/- 0.11(sys)) x 10(-3). We note that B(D-0 -> omega eta) is measured for the first time and that B(D-0 -> eta eta) is measured with much improved precision.

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Anastasi, A.; Babusci, D.; Berlowski, M.; Bloise, C. et al.

### Combination of KLOE sigma (e(+) e(-) -> pi(+)pi(-) gamma(gamma)) measurements and determination of a(mu)(pi+pi-) in the energy range 0.10 < s < 0.95 GeV2

Ingår i Journal of High Energy Physics (JHEP), 2018.

#### Abstract

The three precision measurements of the cross section sigma (e(+)e(-) -> pi(+)pi(-)gamma(gamma)) using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. We present the construction of these covariance matrices and use them to determine a combined KLOE measurement for sigma (e(+)e(-) -> pi(+)pi(-)gamma(gamma)). We find, from this combination, a two-pion contribution to the muon magnetic anomaly in the energy range 0.10 < s < 0.95 GeV2 of a(mu)(pi+pi-) (489.8 +/- 1.7(stat) +/- 4.8(sys)) x 10(-10).

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Improved measurements of X-cJ -> Sigma(+) (Sigma)over-bar(-) and Sigma(0)(Sigma)over-bar(0) decays

Ingår i Physical Review D, 2018.

#### Abstract

Using a data sample of (448.1 +/- 2.9) x 10(6) psi (3686) events collected with the BESIII detector at the BEPCII collider, we present measurements of branching fractions for the decays X-cJ -> Sigma(+) (Sigma) over bar (-) and Sigma(0) (Sigma) over bar (0) The decays X-c1.2 -> Sigma(+) (Sigma) over bar (-) and Sigma (Sigma) over bar (0) are observed for the first time, and the branching fractions for X-c0 -> Sigma(+) (Sigma) over bar (-) and Sigma(0) (Sigma) over bar (0) decays are measured with improved precision. The branching fraction ratios between the charged and neutral modes are consistent with the prediction of isospin symmetry.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of e(+)e(-) -> K(K)over-barJ/psi cross sections at center-of-mass energies from 4.189 to 4.600 GeV

Ingår i Physical Review D, 2018.

#### Abstract

We investigate the process e(+)e(-) -> K (K) over barJ/psi at center-of-mass energies from 4.189 to 4.600 GeV using 4.7 fb(-1) of data collected by the BESIII detector at the BEPCII collider. The Born cross sections for the reactions e(+)e(-) -> K(+)K(-)J/psi and K(S)(0)K(S)(0)J/psi are measured as a function of center-of-mass energy. The energy dependence of the cross section for e(+)e(-) -> K(+)K(-)J/psi is shown to differ from that for pi(+)pi(-)J/psi in the region around the Y(4260). In addition, there is evidence for a structure around 4.5 GeV in the e(+)e(-) -> K(+)K(-)J/psi cross section that is not present in pi(+)pi(-)J/psi.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurements of absolute branching fractions for D mesons decays into two pseudoscalar mesons

Ingår i Physical Review D, 2018.

#### Abstract

Using a data sample of e(+)e(-) collision data with an integrated luminosity of 2.93 fb(-1) taken at the center-of-mass energy root s = 3.773 GeV with the BESIII detector operating at the BEPCII storage rings, we measure the absolute branching fractions of the two-body hadronic decays D+ -> pi(+)pi(0), K+pi(0), pi(+)eta., K+eta., pi(+)eta', K+eta', K-S(0)pi(+), (KSK+)-K-0, and D-0 -> pi(+)pi(-), K+ K-, K--/+pi(+/-), K-S(0)pi(0), K-S(0)eta, K-S(0)eta' Our results are consistent with previous measurements within uncertainties. Among them, the branching fractions for D+-> pi(+)pi(0), K+pi(0), pi(+)eta, pi(+)eta', (KSK+)-K-0, (KSK+)-K-0 and D-0 -> K-S(0)pi(0), K-S(0)eta, K-S(0)eta' are determined with improved precision compared to the world average values.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Study of two-photon decays of pseudoscalar mesons via J/Psi radiative decays

Ingår i Physical Review D, 2018.

#### Abstract

Using a sample of 4.48 x 10(8) Psi(3686) events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons pi(0,) eta , eta' , eta(1405), eta(1475), eta(1760), and X(1835) in J/Psi radiative decays using Psi(3686) -> pi(+) pi(-) J/Psi events. The pi(0), eta, and eta' mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be B(J/Psi -> gamma pi(0) -> 3 gamma) = (3.57 +/- 0.12 +/- 0.16) x 10(-5), B(J/Psi -> gamma eta -> 3 gamma) = (4.42 +/- 0.04 +/- 0.18) x 10(-4), and B(J/Psi -> gamma eta' -> 2 gamma) = (1.26 +/- 0.02 +/- 0.05) x 10(-4), where the first error is statistical and the second is systematic. No clear signal for eta(1405), eta(1475), eta(1760) or X(1835) is observed in the two- photon mass spectra, and upper limits at the 90% confidence level on the product branching fractions are obtained.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of the absolute branching fraction of D*(s0) (2317)(+/-) -> pi D-0(s)+/-

Ingår i Physical Review D, 2018.

#### Abstract

The process e(+)e(-) -> D*D-+(s)*(s0) (2317)(-) + c.c. is observed for the first time with the data sample of 567 pb(-1) collected with the BESIII detector operating at the BEPCII collider at a center-of-mass energy root s = 4.6 GeV. The statistical significance of the D*(s0) (2317)(+/-) signal is 5.8 sigma and the mass is measured to be (2318.3 +/- 1.2 +/- 1.2) MeV/c(2). The absolute branching fraction B(D*(s0) (2317)(+/-) -> pi D-0(s)+/-) is measured as 1.00(-0.14)(+0.00) (stat)(-0.14)(+0.00) (syst) for the first time. The uncertainties are statistical and systematic, respectively.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Search for h(c) -> pi(+)pi(-) J/psi via psi(3686) -> pi(0)pi(+)pi(-) J/psi

Ingår i Physical Review D, 2018.

#### Abstract

Using a data sample of 448.1 x 10(6) psi(3686) events collected with the BESIII detector operating at the BEPCII, we perform search for the hadronic transition h(c)-> pi(+)pi(-) J/psi via psi (3686) -> pi(0)hc. No signals of the transition are observed, and the upper limit on the product branching fraction B(sigma(3686) -> pi(0)h(c))B(h(c) -> pi(+)pi(-) J/psi) at the 90% confidence level (C. L.) is determined to be 2.0 x 10(-6). This is the most stringent upper limit to date.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Precision Measurement of the e(+)e(-) -> Lambda(+)(c)(Lambda)over-bar(c)(-) Cross Section Near Threshold

Ingår i Physical Review Letters, 2018.

#### Abstract

The cross section of the e(+)e(-) -> Lambda(+)(c)(Lambda) over bar (-)(c) process is measured with unprecedented precision using data collected with the BESIII detector at root s = 4574.5, 4580.0, 4590.0 and 4599.5 MeV. The nonzero cross section near the Lambda(+)(c)(Lambda) over bar (-)(c) production threshold is cleared. At center-of-mass energies root s = 4574.5 and 4599.5 MeV, the higher statistics data enable us to measure the Lambda(c) polar angle distributions. From these, the.c electric over magnetic form-factor ratios (vertical bar G(E)/G(M)vertical bar) are measured for the first time. They are found to be 1.14 +/- 0.14 +/- 0.07 and 1.23 +/- 0.05 +/- 0.03, respectively, where the first uncertainties are statistical and the second are systematic.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Search for the rare decays D -> h(h((')))e(+) e(-)

Ingår i Physical Review D, 2018.

#### Abstract

We search for rare decays of D mesons to hadrons accompanied by an electron-positron pair (h(h((')))e(+)e(- )),using an e(+)e(-) collision sample corresponding to an integrated luminosity of 2.93 fb(-1) collected with the BESIII detector at root s = 3.773 GeV. No significant signals are observed, and the corresponding upper limits on the branching fractions at the 90% confidence level are determined. The sensitivities of the results are at the level of 10(-5)-10(-6), providing a large improvement over previous searches.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Search for the rare decay of ψ(3686)→Λ+c¯pe+e−+c.c. at BESIII

Ingår i Physical Review D, 2018.

#### Abstract

Based on a data sample of (448.1 +/- 2.9) x 10(6)Psi(3686) decays collected with the BESIII experiment, a search for the flavor changing neutral current transition Psi(3686) -> Lambda(+)(c) pe(+) e(-) + c.c. is performed for the first time. No signal candidates are observed and the upper limit on the branching fraction of Psi(3686) -> Lambda(+)(c) pe(+) e(-) is determined to be 1.7 x 10(-6) at the 90% confidence level. The result is consistent with expectations from the standard model, and no evidence for new physics is found.

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• Artikel i tidskrift

Husek, Tomas; Kampf, Karol; Novotny, Jiri; Leupold, Stefan

### Radiative corrections to the η(') Dalitz decays

Ingår i Physical Review D, 2018.

#### Abstract

We provide the complete set of radiative corrections to the Dalitz decays eta(()'()) -> l(+)l(-)gamma beyond the softphoton approximation, i. e., over the whole range of the Dalitz plot and with no restrictions on the energy of a radiative photon. The corrections inevitably depend on the eta(()'()) -> gamma*gamma(*) transition form factors. For the singly virtual transition form factor appearing, e.g., in the bremsstrahlung correction, recent dispersive calculations are used. For the one-photon-irreducible contribution at the one-loop level (for the doubly virtual form factor), we use a vector-meson-dominance-inspired model while taking into account the eta-eta' mixing.

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• Artikel, forskningsöversikt

Fang, Shuang-shi; Kupsc, Andrzej; Wei, Dai-hui

### An overview of eta and eta ' decays at BESIII

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2018.

#### Abstract

The world's largest sample of J/psi) events, 1.31 billion events accumulated at the BESIII detector, provides a unique opportunity to investigate eta and eta' physics via two-body J/psi radiative or hadronic decays. For many eta' decay channels the low background data samples are up to three orders of magnitude larger than collected in any previous experiment. Here we review the most significant results on eta and eta' obtained at BESIII so far. The analyses range from detailed studies of common decay dynamics, observations of new radiative and Dalitz decays, and searches for rare/forbidden decays with sensitivity up to B similar to 10(-5). Finally, prospects of forthcoming runs at the J/psi peak for eta and eta' physics are discussed.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of the integrated Luminosities of cross-section scan data samples around the psi(3770) mass region

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2018.

#### Abstract

To investigate the nature of the psi(3770) resonance and to measure the cross section for e(+)e(-) -> D (D) over bar, a cross-section scan data sample, distributed among 41 center-of-mass energy points from 3.73 to 3.89 GeV, was taken with the BESIII detector operated at the BEPCII collider in the year 2010. By analyzing the large angle Bhabha scattering events, we measure the integrated luminosity of the data sample at each center-of-mass energy point. The total integrated luminosity of the data sample is 76.16 +/- 0.04 +/- 0.61 pb(-1), where the first uncertainty is statistical and the second systematic.

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• Artikel i tidskrift

Luo, X. L.; Modamio, V.; Nyberg, Johan; Valiente-Dobon, J. J. et al.

### Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 59-65, 2018.

#### Abstract

The issue of pulse pile-up is frequently encountered in nuclear experiments involving high counting rates, which will distort the pulse shapes and the energy spectra. A digital method of off-line processing of pile-up pulses is presented. The pile-up pulses were firstly identified by detecting the downward-going zero-crossings in the first-order derivative of the original signal, and then the constituent pulses were reconstructed based on comparing the pile-up pulse with four models that are generated by combining pairs of neutron and.. standard pulses together with a controllable time interval. The accuracy of this method in resolving the pile-up events was investigated as a function of the time interval between two pulses constituting a pile-up event. The obtained results show that the method is capable of disentangling two pulses with a time interval among them down to 20 ns, as well as classifying them as neutrons or gamma rays. Furthermore, the error of reconstructing pile-up pulses could be kept below 6% when successive peaks were separated by more than 50 ns. By applying the method in a high counting rate of pile-up events measurement of the NEutron Detector Array (NEDA), it was empirically found that this method can reconstruct the pile-up pulses and perform neutron-gamma discrimination quite accurately. It can also significantly correct the distorted pulse height spectrum due to pile-up events.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Study of the decays D+-> eta(('))e(+)nu(e)

Ingår i Physical Review D, 2018.

#### Abstract

The charm semileptonic decays D+ -> eta e(+)nu(e) and D+ -> eta'e(+)nu(e) are studied with a sample of e(+)e(-) collision data corresponding to an integrated luminosity of 2.93 fb(-1) collected at root s = 3.773 GeV with the BESIII detector. We measure the branching fractions for D+ -> eta e(+)upsilon(e) to be (10.74 +/- 0.81 +/- 0.51)x10(-4), and for D+ -> eta'e(+)nu(e) to be (1.91 +/- 0.51 +/- 0.13) x 10(-4), where the uncertainties are statistical and systematic, respectively. In addition, we perform a measurement of the form factor in the decay D+ -> eta e(+)nu(e) . All the results are consistent with those obtained by the CLEO-c experiment.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Importance of d-wave contributions in the charge symmetry breaking reaction dd -> He-4 pi(0)

Ingår i Physics Letters B, s. 645-650, 2018.

#### Abstract

This letter reports a first quantitative analysis of the contribution of higher partial waves in the charge symmetry breaking reaction dd -> He-4 pi(0) using the WASA-at-COSY detector setup at an excess energy of Q = 60 MeV. The determined differential cross section can be parametrized as d sigma/d Omega = a + b cos(2) theta*, where theta* is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are a = (1.55 +/- 0.46(stat)(-0.8)(+0.32)(syst)) pb/sr and b = (13.1 +/- 2.1(stat)(-2.7)(+1.0)(syst)) pb/sr. The data are compatible with vanishing p-waves and a sizable d-wave contribution. This finding should strongly constrain the contribution of the A isobar to the dd -> He-4 pi(0) reaction and is, therefore, crucial for a quantitative understanding of quark mass effects in nuclear production reactions.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of singly Cabibbo-suppressed decays D-0 → π0π0π0, π0π0η, π0ηη and ηηη

Ingår i Physics Letters B, s. 368-375, 2018.

#### Abstract

Using a data sample of e(+)e(-) collision data corresponding to an integrated luminosity of 2.93 fb(-1) collected with the BESIII detector at a center-of-mass energy of root s = 3.773 GeV, we search for the singly Cabibbo-suppressed decays D-0 -> pi(0)pi(0)pi(0), pi(0)pi(0)eta, pi(0)eta eta and eta eta eta using the double tag method. The absolute branching fractions are measured to be B(D-0 -> pi(0)pi(0)pi(0)) = (2.0 +/- 0.4 +/- 0.3) x 10(-4), B(D-0 -> pi(0)pi(0)eta) = (3.8 +/- 1.1 +/- 0.7) x 10(-4) and B(D-0 -> pi(0)eta eta) = (7.3 +/- 1.6 +/- 1.5) x 10(-4) with the statistical significances of 4.8 sigma, 3.8 sigma and 5.5 sigma, respectively, where the first uncertainties are statistical and the second ones systematic. No significant signal of D-0 -> eta eta eta is found, and the upper limit on its decay branching fraction is set to be B(D-0 -> eta eta eta) < 1.3 x 10(-4) at the 90% confidence level.

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• Artikel i tidskrift

Holmberg, Måns; Leupold, Stefan

### The relativistic chiral Lagrangian for decuplet and octet baryons at next-to-leading order

Ingår i European Physical Journal A, 2018.

#### Abstract

A complete and minimal relativistic Lagrangian is constructed at next-to-leading order for SU(3) chiral perturbation theory in the presence of baryon octet and baryon decuplet states. The Lagrangian has 13 terms for the pure decuplet sector, 6 terms for the transition sector from baryon octet to decuplet and (as already known from the literature) 16 terms for the pure octet sector. The minimal field content of 25 of these terms is meson-baryon four-point interactions. 3 terms give rise to the mass splitting for baryon octet and decuplet states, respectively. 2 terms give rise to overall mass shifts. 4 terms provide anomalous magnetic moments and a decuplet-to-octet magnetic transition moment. 1 term leads to an axial vector transition moment. It is shown that meson-baryon three-point coupling constants come in at leading order whereas no additional one appears in the minimal Lagrangian at next-to-leading order. Those low-energy constants that give rise to mass splitting and magnetic moments, respectively, are determined. Predictions are provided for radiative decays of decuplet to octet baryons.

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• Artikel i tidskrift

Buchheim, T.; Hilger, T.; Kämpfer, B.; Leupold, Stefan

### Chiral-partner D mesons in a heat bath within QCD sum rules

Ingår i Journal of Physics G, 2018.

#### Abstract

Utilizing QCD sum rules, we extract the temperature dependences of the spectral properties of the pseudo-scalar and scalar D mesons regarded as chiral partners. Besides the masses also decay constants are analyzed as the D meson yields in heavy-ion collisions may be sensitive to their altered decay properties in an ambient strongly interacting medium. Our findings are (i) a decreasing scalar D meson mass for growing temperatures while its pseudo-scalar partner meson seems hardly affected, which is in qualitative agreement with hadronic model calculations; (ii) inferring an equally weak temperature dependence of the pseudo-scalar D meson decay properties the decreasing residua and decay constants of the scalar particle point towards partial chiral restoration. As a bonus of our analysis in the pseudo-scalar sector we determine the pseudoscalar decay constant at vanishing temperature. Due to the connection to particular leptonic branching fractions this decay constant is of great interest allowing for the determination of the off-diagonal CKM matrix element vertical bar V-cd vertical bar at zero temperature.

• Artikel i tidskrift

Boso, A.; Lenzi, S. M.; Recchia, F.; Bonnard, J. et al.

### Neutron Skin Effects in Mirror Energy Differences: The Case of Mg-23-Na-23

Ingår i Physical Review Letters, 2018.

#### Abstract

Energy differences between analogue states in the T = 1/2 Mg-23-Na-23 mirror nuclei have been measured along the rotational yrast bands. This allows us to search for effects arising from isospin-symmetrybreaking interactions (ISB) and/or shape changes. Data are interpreted in the shell model framework following the method successfully applied to nuclei in the f(7/2) shell. It is shown that the introduction of a schematic ISB interaction of the same type of that used in the f(7/2) shell is needed to reproduce the data. An alternative novel description, applied here for the first time, relies on the use of an effective interaction deduced from a realistic charge-dependent chiral nucleon-nucleon potential. This analysis provides two important results: (i) The mirror energy differences give direct insight into the nuclear skin; (ii) the skin changes along the rotational bands are strongly correlated with the difference between the neutron and proton occupations of the s(1/2) "halo" orbit.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of e(+)e(-) -> D(D)over-bar cross sections at the psi(3770) resonance

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2018.

#### Abstract

We report new measurements of the cross sections for the production of D (D) over bar final states at the psi(3770) resonance. Our data sample consists of an integrated luminosity of 2.93 fb(-1) of e(+)e(-) annihilation data produced by the BEPCII collider and collected and analyzed with the BESIII detector. We exclusively reconstruct three D-0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed D (D) over bar events ("double tags") to the yield of all reconstructed D or (D) over bar mesons ("single tags") to determine the number of D-0(D) over bar (0) and D+D- events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be sigma(e(+)e(-) -> D-0(D) over bar (0)(-) )=(3.615 +/- 0.010 +/- 0.038) nb and sigma(e(+)e(-) -> D+D-)=(2.830 +/- 0.011 +/- 0.026) nb, where the uncertainties are statistical and systematic, respectively.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Observation of a(0)(0)(980)-f(0)(980) Mixing

Ingår i Physical Review Letters, 2018.

#### Abstract

We report the first observation of a(0)(0)(980)-f(0)(980) mixing in the decays of J/psi -> phi f(0)(980) -> phi a(0)(0)(980) -> phi eta pi(0) and chi(c1) -> a(0)(0)(980)pi(0) -> f(0)(980)pi(0)->pi(+)pi(-)pi(0), using data samples of 1.31 x 10(9) J/psi events and 4.48 x 10(8) psi (3686) events accumulated with the BESIII detector. The signals of f(0)(980) -> a(0)(0)(980) and a(0)(0)(980) -> f(0)(980) mixing are observed at levels of statistical significance of 7.4 sigma and 5.5 sigma, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, g(a0K+K-) and g(f0K+K-), are estimated. The results improve the understanding of the nature of a(0)(0)(980) and f(0)(980).

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Observation of the Semileptonic Decay D-0 -> a(0)(980)(-)e(+)nu(e) and Evidence for D+ -> a(0)(980)(0)e(+)nu(e)

Ingår i Physical Review Letters, 2018.

#### Abstract

Using an e(+)e(-) collision data sample of 2.93 fb(-1) collected at a center-of-mass energy of 3.773 GeV by the BESIII detector at BEPCII, we report the observation of D-0 -> a(0)(980)(-)e(+)nu(e) and evidence for D+ -> a(0)(980)(0)e(+)nu(e) with significances of 6.4 sigma and 2.9 sigma, respectively. The absolute branching fractions are determined to be B(D-0 -> a(0)(980)(-)e(+)nu(e)) x B(a(0)(980)(-) -> eta pi(-)) = [1.33(-0.29)(+0.33)(stat) +/- 0.09(syst)] x 10(-4) and B(D+ -> a(0)(980)(0)e(+)nu(e)) x B(a(0)(980)(0) -> eta pi(0)) = [1.66(-0.66)(+0.81)(stat) +/- 0.11(syst) x 10(-4). This is the first time the a(0)(980) meson has been measured in a D-0 semileptonic decay, which would open one more interesting page in the investigation of the nature of the puzzling a(0)(980) states.

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• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Isotensor Dibaryon in the pp -> pp pi(+)pi(-) Reaction?

Ingår i Physical Review Letters, 2018.

#### Abstract

Exclusive measurements of the quasifree pp -> pp pi(+)pi(-) reaction have been carried out at WASA@ COSY by means of pd collisions at T-p = 1.2 GeV. Total and differential cross sections have been extracted covering the energy region T-p = 1.08-1.36 GeV, which is the region of N* (1440) and Delta(123)Delta(1232) resonance excitations. Calculations describing these excitations by t-channel meson exchange are at variance with the measured differential cross sections and underpredict substantially the experimental total cross section. An isotensor Delta N dibaryon resonance with I(J(P)) = 2(1(+)) produced associatedly with a pion is able to overcome these deficiencies.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### First measurement of e(+)e(-) -> pK(S)(0)(n)over-barK(-) + c.c. above open charm threshold

Ingår i Physical Review D, 2018.

#### Abstract

The process e(+)e(-) -> pK(S)(0)(n) over barK(-) + c.c. and its intermediate processes are studied for the first time, using data samples collected with the BESIII detector at BEPCII at center-of-mass energies of 3.773, 4.008, 4.226, 4.258, 4.358, 4.416, and 4.600 GeV, with a total integrated luminosity of 7.4 fb(-1). The Born cross section of e(+)e(-) -> pK(S)(0)(n) over barK(-) + c.c. is measured at each center-of-mass energy, but no significant resonant structure in the measured cross-section line shape between 3.773 and 4.600 GeV is observed. No evident structure is detected in the pK(-), nK(S)(0), pK(S)(0), nK(+), p (n) over bar, or (KSK-)-K-0 invariant mass distributions except for Lambda(1520). The Born cross sections of e(+)e(-) -> Lambda(1520)(n) over barK(S)(0) + c.c. and e(+)e(-) -> Lambda(1520)(p) over barK(+) + c.c. are measured, and the 90% confidence level upper limits on the Born cross sections of e(+)e(-) -> Lambda(1520)(Lambda) over bar (1520) are determined at the seven center-of-mass energies. There is an evident difference in line shape and magnitude of the measured cross sections between e(+)e(-) -> Lambda(1520)(-> pK(-))(n) over barK(S)(0) and e(+)e(-) -> pK-(Lambda) over bar (1520)(-> (n) over barK(S)(0)).

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• Artikel i tidskrift

Anastasi, A.; Babusci, D.; Berlowski, M.; Bloise, C. et al.

### Measurement of the charge asymmetry for the K-S -> pi e nu decay and test of CPT symmetry with the KLOE detector

Ingår i Journal of High Energy Physics (JHEP), 2018.

#### Abstract

Using 1.63 fb(-1) of integrated luminosity collected by the KLOE experiment about 7 x 10(4) K-S -> pi(+/-)e(-/+)nu decays have been reconstructed. The measured value of the charge asymmetry for this decay is A(S) = (-4.9 +/- 5.7(stat) +/- 2.6(syst)) x 10(-3) which is almost twice more precise than the previous KLOE result. The combination of these two measurements gives A(S) = (3.8 +/- 5.0(stat) +/- 2.6(syst)) x 10(-3) and, together with the asymmetry of the K-L semileptonic decay, provides significant tests of the CPT symmetry. The obtained results are in agreement with CPT invariance.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of the Absolute Branching Fraction of the Inclusive Decay Lambda(+)(c) -> Lambda plus X

Ingår i Physical Review Letters, 2018.

#### Abstract

Based on an e(+)e(-) collision data sample corresponding to an integrated luminosity of 567 pb(-1) taken at the center-of-mass energy of root s = 4.6 GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive decay Lambda(+)(c) -> Lambda + X to be B(Lambda(+)(c) -> Lambda + X) = (38.2(-2.2)(+2.8) +/- 0.9)% using the double-tag method, where X refers to any possible final state particles. In addition, we search for direct CP violation in the charge asymmetry of this inclusive decay for the first time, and obtain A(CP) [B(Lambda(+)(c) -> Lambda + X) - B((Lambda) over bar (-)(c) -> (Lambda) over bar + X)]/[B(Lambda(+)(c) -> Lambda + X) + B((Lambda) over bar (-)(c) -> (Lambda) over bar + X)] = (2.1(-6.6)(+7.0) +/- 1.6)%, a statistically limited result with no evidence of CP violation.

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• Artikel i tidskrift

Aghasyan, M.; Akhunzyanov, R.; Alexeev, M. G.; Alexeev, G. D. et al.

### Search for muoproduction of X(3872) at COMPASS and indication of a new state (X)over-tilde(3872)

Ingår i Physics Letters B, s. 334-340, 2018.

#### Abstract

We have searched for exclusive production of exotic charmonia in the reaction mu N+ -> mu(+)(J/psi pi(+)pi(-))pi N-+/-' using COMPASS data collected with incoming muons of 160 GeV/c and 200 GeV/c momentum. In the J/psi pi(vertical bar)pi mass distribution we observe a signal with a statistical significance of 4.1 sigma. Its mass and width are consistent with those of the X(3872). The shape of the pi(+)pi(-) mass distribution from the observed decay into J/psi pi(+)pi(-) shows disagreement with previous observations for X(3872). The observed signal may be interpreted as a possible evidence of a new charmonium state. It could be associated with a neutral partner of X(3872) with C=-1 predicted by a tetraquark model. The product of cross section and branching fraction of the decay of the observed state into J/psi pi(+)pi(-) is determined to be 71 +/- 28(stat)+/- 39(syst) pb.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurements of absolute branching fractions for Lambda(+)(c) -> Xi K-0(+) and Xi(1530)K-0(+)

Ingår i Physics Letters B, s. 200-206, 2018.

#### Abstract

We report the first measurements of absolute branching fractions for the W-exchange-only processes Lambda(+)(c) -> Xi K-0(+) and Lambda(+)(c)-> Xi(1530)K-0(+) with the double-tag technique, by analyzing an e(+)e(-) collision data sample, that corresponds to an integrated luminosity of 567 pb(-1) collected at a center-of-mass energy of 4.6 GeV by the BESIII detector. The branching fractions are measured to be B(Lambda(+)(c)-> Xi K-0(+)) = (5.90 +/- 0.86 +/- 0.39) x 10(-3) and B(Lambda(+)(c)-> Xi(1530)K-0(+)) = (5.02 +/- 0.99 +/- 0.31) x 10(-3), where the first uncertainties are statistical and the second systematic. Our results are more precise than the previous relative measurements.

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• Artikel i tidskrift

Ablikim, M.; Collaboration, B. E. S. I. I. I.; Achasov, M. N.; Ahmed, S. et al.

### Observation of ψ(3686)→n¯n and improved measurement of ψ(3686)→p¯p

Ingår i Physical Review D, 2018.

#### Abstract

We observe the decay psi (3686) -> n (n) over bar for the first time and measure psi (3686) -> p (p) over bar with improved accuracy by using 1.07 x 10(8) psi (3686) events collected with the BESIII detector. The measured branching fractions are B(psi(3686) -> n (n) over bar) = (3.06 +/- 0.06 +/- 0.14) x 10(-4) and B(psi(3686) -> p (p) over bar) = (3.05 +/- 0.02 +/- 0.12) x 10(-4). Here, the first uncertainties are statistical, and the second ones are systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey 1 + alpha cos(2) theta, we determine the a parameters to be alpha(n (n) over bar) = 0.68 +/- 0.12 +/- 0.11 and alpha(p (p) over bar) = 1.03 +/- 0.06 +/- 0.03 for psi(3686) -> n (n) over bar and psi(3686) -> p (p) over bar, respectively.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Observation of psi(3686) -> eta ' e(+)e(-)

Ingår i Physics Letters B, s. 452-458, 2018.

#### Abstract

Using a data sample of 448.1 x 10(6) psi(3686) events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay psi(3686) -> eta'e(+)e(-), with significances of 7.0 sigma and 6.3 sigma when reconstructing the eta' meson via its decay modes eta' -> gamma pi(+)pi(-) and eta' -> pi(+)pi(-) eta (eta -> gamma gamma), respectively. The weighted average branching fraction is determined to be B(psi(3686) -> eta'e(+)e(-)) = (1.90 +/- 0.25 +/- 0.11) x 10(-6), where the first uncertainty is statistical and the second systematic.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Search for invisible decays of omega and phi with J/psi data at BESIII

Ingår i Physical Review D, 2018.

#### Abstract

Using a data sample of (1310.6 +/- 7.0) x 10(6) J/psi events collected with the BESIII detector operating at the BEPCII collider, we perform the first experimental search for invisible decays of a light vector meson (V = omega, phi) via J/psi -> V-eta decays. The decay of eta -> pi(+)pi(-)pi(0) is utilized to tag the V meson decaying into the invisible final state. No evidence for a significant invisible signal is observed, and the upper limits on the ratio of branching fractions at the 90% confidence level are determined to be B(omega -> invisible)/B(omega -> pi(+)pi(-)pi(0)) < 8.1 x 10(-5) and B(phi -> invisible)/B(phi -> K+K-) < 3.4 x 10(-4). By using the world average values of B(omega -> pi(+)pi(-)pi(0) and B(phi -> K+K-,) the upper limits on the decay branching fractions at the 90% confidence level are set as B(omega -> invisible) < 7.3 x 10(-5) and B(phi -> invisible) < 1.7 x 10(-4), respectively.

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• Artikel i tidskrift

Hoferichter, Martin; Hoid, Bai-Long; Kubis, Bastian; Leupold, Stefan et al.

### Pion-Pole Contribution to Hadronic Light-By-Light Scattering in the Anomalous Magnetic Moment of the Muon

Ingår i Physical Review Letters, 2018.

#### Abstract

The pi(0) pole constitutes the lowest-lying singularity of the hadronic light-by-light (HLBL) tensor, and thus, it provides the leading contribution in a dispersive approach to HLBL scattering in the anomalous magnetic moment of the muon (g - 2)(mu). It is unambiguously defined in terms of the doubly virtual pion transition form factor, which in principle, can be accessed in its entirety by experiment. We demonstrate that, in the absence of a direct measurement, the full spacelike doubly virtual form factor can be reconstructed very accurately based on existing data for e(+)e(-) -> 3 pi, e(+)e(-)-> e(+)e(-)pi(0), and the pi(0) -> gamma gamma decay width. We derive a representation that incorporates all the low-lying singularities of the form factor, matches correctly onto the asymptotic behavior expected from perturbative QCD, and is suitable for the evaluation of the (g - 2)(mu) loop integral. The resulting value, a(mu)(pi 0-pole) = 62.6(-2.5)(+3.0) x 10(-11), for the first time, represents a complete data-driven determination of the pion-pole contribution with fully controlled uncertainty estimates. In particular, we show that already improved singly virtual measurements alone would allow one to further reduce the uncertainty in a(mu)(pi 0-pole).

Open access
• Artikel i tidskrift

Ertoprak, A.; Cederwall, B.; Qi, C.; Doncel, M. et al.

### M1 And E2 Transition Rates From Core-Excited States In Semi-Magic Ru-94

Ingår i European Physical Journal A, 2018.

#### Abstract

Lifetimes of high-spin states have been measured in the semi-magic (N = 50) nucleus Ru-94. Excited states in Ru-94 were populated in the Ni-58(Ca-40, 4p)Ru-94* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from gamma-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm(2) metallic Ni-58 target. In total eight excited-state lifetimes in the angular momentum range I = (13-20)h have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.

• Artikel i tidskrift

Adlarson, Patrik; Collaboration, WASA-at-COSY; Augustyniak, W.; Bardan, W. et al.

### Search for C violation in the decay eta -> pi(0)e(+)e(-) with WASA-at-COSY

Ingår i Physics Letters B, s. 378-384, 2018.

#### Abstract

We report on the search for the rare decay eta -> pi(0)e(+)e(-) which is of interest to study C violation in the electromagnetic interaction which would indicate contributions from physics beyond the Standard Model, since the allowed decay via a two-photon intermediate state is strongly suppressed. The experiment has been performed using the WASA-at-COSY installation, located at the COSY accelerator of the Forschungszentrum Julich, Germany. In total 3 x 10(7) events of the reaction pd -> He-3 eta have been recorded at an excess energy of Q = 59.8MeV. Based on this data set the C parity violating decay eta -> pi(0)gamma* -> pi(0)e(+)e(-) via a single-photon intermediate state has been searched for, resulting in new upper limits of Gamma(eta -> pi(0)e(+) e(-))/Gamma(eta -> pi(+) pi(-) pi(0)) < 3.28 x 10(-5) and Gamma(eta -> pi(0)e(+) e(-))/Gamma(eta -> all)< 7.5 x 10(-6) (CL=90%), respectively.

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• Artikel i tidskrift

Anastasi, A.; Babusci, D.; Berlowski, M.; Bloise, C. et al.

### Combined limit on the production of a light gauge boson decaying into mu(+) mu(-) and pi(+) pi(-)

Ingår i Physics Letters B, s. 336-341, 2018.

#### Abstract

We searched for the mu(+) mu(-) decay of a light vector gauge boson, also known as dark photon, in the e(+) e(-) -> mu(+) mu(-) gamma(ISR) process by means of the Initial State Radiation (ISR) method. We used 1.93fb(-1) of data collected by the KLOE experiment at the DA Phi NE phi-factory. No structures have been observed over the irreducible mu(+) mu(-) background. A 90% CL limit on the ratio epsilon(2)= alpha'/alpha between the dark coupling constant and the fine structure constant of 3 x 10(-6)-2 x 10(-7) has been set in the dark photon mass region between 519 MeV and 973 MeV. This new limit has been combined with the published result obtained investigating the hypothesis of the dark photon decaying into hadrons in e(+) e(-) -> pi(+) pi(-) gamma(ISR) events. The combined 90% CL limit increases the sensitivity especially in the rho-omega interference region and excludes epsilon(2) greater than (13 - 2) x 10(-7). For dark photon masses greater than 600 MeV the combined limit is lower than 8 x 10(-7) resulting more stringent than present constraints from other experiments.

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Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Backward single-pion production in the pd -> He-3 pi(0)reaction with WASA-at-COSY

Ingår i European Physical Journal A, 2018.

#### Abstract

New data on the production of single neutral pions in the pd -> He-3 pi(0) reaction are presented. For fifteen proton beam momenta between p(p) = 1.60GeV/c and p(p) = 1.74 GeV/c, differential cross sections are determined over a large fraction of the backward hemisphere. Since the only previous systematic measurements of single-pion production at these energies were made in collinear kinematics, the present work constitutes a significant extension of the current knowledge on this reaction. Even this far above the production threshold, significant changes are found in the behaviour of the angular distributions over small intervals in beam momentum.

• Konferensbidrag

Perotti, Elisabetta

### Extraction of Polarization Parameters in the ‾pp → Ω̄Ω Reaction

Ingår i FAIRNESS 2017, 2018.

#### Abstract

A method to extract the polarization of Omega hyperons produced via the strong interaction is presented. Assuming they are spin 3/2 particles, the corresponding spin density matrix can be written in terms of seven non-zero polarization parameters, all retrievable from the angular distribution of the decay products. Moreover by considering the full decay chain Omega ->Lambda K -> p pi K the magnitude of the asymmetry parameters beta Omega and gamma Omega can be obtained. This method, applied here to the specific Omega case, can be generalized to any weakly decaying hyperon and is perfectly suited for the PANDA experiment where hyperon-antihyperon pairs will be copiously produced in proton-antiproton collisions. The aim is to take a step forward towards the understanding of the mechanism that reigns strangeness production in these processes.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Amplitude analysis of the KSKS system produced in radiative J /psi decays

Ingår i Physical Review D, 2018.

#### Abstract

An amplitude analysis of the KSKS system produced in radiative J/psi decays is performed using the (1310.6 +/- 7.0) x 10(6) nip decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parametrizing the KSKS invariant mass spectrum as a sum of Breit-aligner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the KSKS system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the f(0)(1710), f(0)(2200), and f(2)'(1525). The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative J/psi decays to KSKS is measured to be (8.1 +/- 0.4) x 10(-4), where the uncertainty is systematic and the statistical uncertainty is negligible.

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• Artikel i tidskrift

Hoferichter, Martin; Hoid, Bai-Long; Kubis, Bastian; Leupold, Stefan et al.

### Dispersion relation for hadronic light-by-light scattering: pion pole

Ingår i Journal of High Energy Physics (JHEP), 2018.

#### Abstract

The pion-pole contribution to hadronic light-by-light scattering in the anomalous magnetic moment of the muon (g - 2) is fully determined by the doubly-virtual pion transition form factor. Although this crucial input quantity is, in principle, directly accessible in experiment, a complete measurement covering all kinematic regions relevant for (g -2) is not realistic in the foreseeable future. Here, we report in detail on a reconstruction from available data, both space- and time-like, using a dispersive representation that accounts for all the low-lying singularities, reproduces the correct high- and low-energy limits, and proves convenient for the evaluation of the (g - 2) loop integral. We concentrate on the systematics of the fit to e(+)e(-) 3 data, which are key in constraining the isoscalar dependence, as well as the matching to the asymptotic limits. In particular, we provide a detailed account of the pion transition form factor at low energies in the time- and space-like region, including the error estimates underlying our final result for the pion-pole contribution, a(mu)(pi 0) (-pole) = 62.6(-2.5)(+3.0) x 10(-11),, and demonstrate how forthcoming singly-virtual measurements will further reduce its uncertainty.

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurement of the Branching Fraction For the Semileptonic Decay D0(+) -> pi(-(0))mu(+)nu(mu )and Test of Lepton Flavor Universality

Ingår i Physical Review Letters, 2018.

#### Abstract

Using a data sample corresponding to an integrated luminosity of 2.93 fb(-1) taken at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we perform an analysis of the semileptonic decays D0(+) -> pi(-(0))mu(+)nu(mu ). The branching fractions of D-0 -> pi(-)mu(+)nu(mu), and D+ -> pi(0)mu(+)nu(mu ) are measured to be (0.272 +/- 0.008(start) +/- 0.006(syst))% and (0.350 +/- 0.011(star) +/- 0.010(syst))%, respectively, where the former is of much improved precision compared to previous results and the latter is determined for the first time. Using these results along with previous BESIII measurements of D0(+) -> pi(-(0))e(+)nu(e), we calculate the branching fraction ratios to be R-0 BD0 -> pi(-)mu(+)nu mu BD0 -> pi(-)e(+)nu e=0.922 +/- 0.030(start) +/- 0.022(syst) and R+ BD+ -> pi(0)mu(+)nu mu/BD+ -> pi(0)e(+)nu e= 0.964 +/- 0.037(start) +/- 0.026(syst), which arc compatible with the theoretical expectation of lepton flavor universality within 1.7 sigma and 0.5 sigma, respectively. We also examine the branching fraction ratios in different four-momentum transfer square regions, and find no significant deviations from the standard model predictions.

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• Artikel i tidskrift

Delafosse, C.; Verney, D.; Marevic, P.; Gottardo, A. et al.

### Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the Ni-78 Region: A Hint from Lifetime Measurements

Ingår i Physical Review Letters, 2018.

#### Abstract

Lifetime measurements of excited states of the light N = 52 isotones Kr-88, Se-86, and Ge-84 have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B(E2; 2(+)-> 0(+)) and B(E2; 4(+)-> 2(+)) were obtained for the first time for the hard-to-reach 84Ge. While the B(E2; 2(+)-> 0(+) ) values of Kr-88, Se-86 saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g(7/2), 1h(11/2)) space of an inert Ni-78 core, the value obtained for Ge-84 largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N less than or similar to 49, extend beyond N = 50. The onset of collectivity at Z = 32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that the latter provides actually reliable guidance for understanding the observed proton and neutron single particle structure in the whole medium-mass region, from Ni to Sn, pointing towards the important role of the isovector-vector rho field in shell-structure evolution.

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• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Total and differential cross sections of η-production in proton–deuteron fusion for excess energies between Qη = 13 MeV and Qη = 81 MeV

Ingår i Physics Letters B, s. 297-304, 2018.

#### Abstract

New data on both total and differential cross sections of the production of eta mesons in proton-deuteron fusion to He-3 eta in the excess energy region 13.6 MeV <= Q(eta) <= 80.9 MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Julich, using a proton beam at 15 different beam momenta between p(p) = 1.60 GeV/c and p(p) = 1.74 GeV/c. While significant structure of the total cross section is observed in the energy region 20 MeV less than or similar to Q(eta) less than or similar to 60 MeV, a previously reported sharp variation around Q(eta) approximate to 50 MeV cannot be confirmed. Angular distributions show the typical forward- peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval.

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• Artikel i tidskrift

Hoferichter, Martin; Hoid, Bai-Long; Kubis, Bastian; Leupold, Stefan et al.

### Dispersion relation for hadronic light-by-light scattering: pion pole

Ingår i Journal of High Energy Physics, s. 141 141-, 2018.

#### Abstract

The pion-pole contribution to hadronic light-by-light scattering in the anomalous magnetic moment of the muon (g − 2)μ is fully determined by the doubly-virtual pion transition form factor. Although this crucial input quantity is, in principle, directly accessible in experiment, a complete measurement covering all kinematic regions relevant for (g −2)μ is not realistic in the foreseeable future. Here, we report in detail on a reconstruction from available data, both space- and time-like, using a dispersive representation that accounts for all the low-lying singularities, reproduces the correct high- and low-energy limits, and proves convenient for the evaluation of the (g − 2)μ loop integral. We concentrate on the systematics of the fit to e+e → 3π data, which are key in constraining the isoscalar dependence, as well as the matching to the asymptotic limits. In particular, we provide a detailed account of the pion transition form factor at low energies in the time- and space-like region, including the error estimates underlying our final result for the pion-pole contribution, a&#x03BC;&#x03C0;0&#x2212;pole=62.6&#x2212;2.5+3.0&#x00D7;10&#x2212;11" role="presentation">aπ0−poleμ=62.6+3.0−2.5×10−11, and demonstrate how forthcoming singly-virtual measurements will further reduce its uncertainty.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Observation of h(1)(1380) in the J/psi -> eta ' K(K)over-bar pi decay

Ingår i Physical Review D, 2018.

#### Abstract

Using 1.31 x 10(9) J/psi events collected by the BESIII detector at the BEPCII e(+)e(-) collider, we report the first observation of the h(1)(1380) in J/psi -> eta'h(1)(1380) with a significance of more than ten standard deviations. The mass and width of the possible axial-vector strangeonium candidate h(1)(1380) are measured to be M = (1423.2 +/- 2.1 +/- 7.3) MeV/c(2) and Gamma = (90.3 +/- 9.8 +/- 17.5) MeV. The product branching fractions, assuming no interference, are determined to be B(J/psi -> eta'h(1)(1380)) x B(h(1)(1380) -> K*(892)K-+(-)+c.c.) = (1.51 +/- 0.09 +/- 0.21) x 10(-4) in eta'K+K-pi(0) mode and B(J/psi -> eta'h(1)(1380)) x B(h(1)(1380) -> K*(892)(K) over bar +c.c.) =(2.16 +/- 0.12 +/- 0.29) x 10(-4) in eta'(KSK +/-)-K-0 pi(-/+) mode. The first uncertainties are statistical and the second are systematic. Isospin symmetry violation is observed in the decays h(1)(1380) K*(892)K-+(-) + c.c. and h(1)(1380) -> K*(892)(0)(K) over bar (0) + c.c.. Based on the measured h(1)(1380) mass, the mixing angle between the states h(1)(1170) and h(1)(1380) is determined to be (35.9 +/- 2.6)degrees, consistent with theoretical expectations.

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Observation of D0(+) -> K-S(0)pi(0(+))eta ' and improved measurement of D-0 -> K-pi(+)eta '

Ingår i Physical Review D, 2018.

#### Abstract

By analyzing an e(+)e(-) data sample corresponding to an integrated luminosity of 2.93 fb(-1) taken at a centerof- mass energy of 3.773 GeV with the BESIII detector, we measure the branching fractions of the Cabibbofavored hadronic decays D-0 -> K- pi' eta', D-0 -> K-s(0)pi(0)eta', which are determined to be (6.43 +/- 0.15(stat)+/- 0.31(syst)) x 10(-3), (2.52 +/- 0.22(stat) +/- 0.15(syst)) x 10(-3,) and (1.90 +/- 0.17(stat) +/- 0.13(syst)) x 10(-3), respectively. The precision of the branching fraction of D-0 -> K- pi(+) eta' is significantly improved, and the processes D-0 -> K-S(0)pi(0)eta' and D+ -> K-S(0) pi(+)eta' are observed for the first time.

• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Dalitz plot analysis of the decay ω→π+π−π0

Ingår i Physical Review D, 2018.

#### Abstract

Using a low-background sample of 2.6 x 10(5) J/psi -> omega eta(omega -> pi(+) pi(-) pi(0), eta -> gamma gamma) events, about 5 times larger statistics than previous experiments, we present a Dalitz plot analysis of the decay omega -> pi(+) pi(-) pi(0). It is found that the Dalitz plot distribution differs from the pure P-wave phase space with a statistical significance of 18.9 sigma. The parameters from the fit to data are in reasonable agreement with those without the cross-channel effect within the dispersive framework, which indicates that the cross-channel effect in omega -> pi(+) pi(-) pi(0) is not significant.

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• Artikel i tidskrift

Ablikim, M.; Andersson, Walter Ikegami; Johansson, Tord; Kupsc, Andrzej et al.

### Measurement of the Absolute Branching Fraction of the Inclusive Semileptonic Λc+ Decay

Ingår i Physical Review Letters, 2018.

#### Abstract

Using a data sample of e(+)e(-) collisions corresponding to an integrated luminosity of 567 pb(-1) collected at a center-of-mass energy of root s = 4.6 GeV with the BESIII detector, we measure the absolute branching fraction of the inclusive semileptonic Lambda(+)(c) decay with a double-tag method. We obtain B(Lambda(+)(c) -> Xe+nu(e)) = (3.95 +/- 0.34 +/- 0.09)%, where the first uncertainty is statistical and the second systematic. Using the known Lambda(+)(c) lifetime and the charge-averaged semileptonic decay width of nonstrange charmed mesons (D-0 and D+), we obtain the ratio of the inclusive semileptonic decay widths Gamma(Lambda(+)(c) -> Xe+nu(e))/(Gamma) over bar (D -> Xe+nu(e)) = 1.26 +/- 0.12.

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• Artikel i tidskrift

Ablikim, M.; Johansson, Tord; Kupsc, Andrzej; Li, Cui et al.

### Precision Study of η′→γπ+π− Decay Dynamics

Ingår i Physical Review Letters, 2018.

#### Abstract

Using a low background data sample of 9.7 x 10(5) J/psi -> gamma eta',eta' -> gamma pi(+)pi(-) events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of eta' -> gamma pi(+)pi(-) are studied with both model-dependent and model-independent approaches. The contributions of. and the rho(770)-omega interference are observed for the first time in the decays eta' -> gamma pi(+)pi(-) in both approaches. Additionally, a contribution from the box anomaly or the rho(1450) resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.

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• Artikel i tidskrift

Aghasyan, M.; Alexeev, M. G.; Alexeev, G. D.; Amoroso, A. et al.

### Light isovector resonances in pi(-) p -> pi(-) pi(-) pi(+)p at 190 GeV/c

Ingår i Physical Review D, 2018.

#### Abstract

We have performed the most comprehensive resonance-model fit of pi(-)pi(-)pi(+) states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction pi(-) + p -> pi(-)pi(-)pi(+) +p(recoil) with a 190 GeV/c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5 < m(3 pi) < 2.5 GeV/c(2), and simultaneously in 11 bins of the reduced four-momentum transfer squared, 0.1 < t'< 1.0 (GeV/c)(2), are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with J(PC) = 0(-+), 1(++), 2(++), 2(-+), 4(++), and spin-exotic 1(-+) quantum numbers. The model contains the well-known resonances pi(1800), a(1)(1260), a(2)(1320), pi(2)(1670), pi(2)(1880), and a(4) (2040). In addition, it includes the disputed pi(1)(1600), the excited states a(1)(1640), a2(1700), and pi(2) (2005), as well as the resonancelike a(1)(1420). We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 t' bins. We extract the relative branching fractions of the rho(770)pi and f(2)(1270)pi decays of a(2)(1320) and a(4)(2040), where the former one is measured for the first time. In a novel approach, we extract the t' dependence of the intensity of the resonances and of their phases. The t' dependence of the intensities of most resonances differs distinctly from the t' dependence of the nonresonant components. For the first time, we determine the t' dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances. We have performed extensive systematic studies on the model dependence and correlations of the measured physical parameters.

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• Artikel i tidskrift

Ablikim, M.; Johansson, Tord; Kupsc, Andrzej; Li, Cui et al.

### Precision Study of eta ' -> gamma pi(+) pi(-) Decay Dynamics

Ingår i Physical Review Letters, 2018.

#### Abstract

Using a low background data sample of 9.7 x 10(5) J/psi -> gamma eta',eta' -> gamma pi(+)pi(-) events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of eta' -> gamma pi(+)pi(-) are studied with both model-dependent and model-independent approaches. The contributions of. and the rho(770)-omega interference are observed for the first time in the decays eta' -> gamma pi(+)pi(-) in both approaches. Additionally, a contribution from the box anomaly or the rho(1450) resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Luminosity measurements for the R scan experiment at BESIII

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2017.

#### Abstract

By analyzing the large-angle Bhabha scattering events e+e- → (γ)e+e- and diphoton events e+e- → (γ)γγ for the data sets collected at center-of-mass (c.m.) energies between 2.2324 and 4.5900 GeV (131 energy points in total) with the upgraded Beijing Spectrometer (BESIII) at the Beijing Electron-Positron Collider (BEPCII), the integrated luminosities have been measured at the different c.m. energies, individually. The results are important inputs for the R value and J/ψ resonance parameter measurements.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of Ψ(3686) → e+e-ΧcJ and ΧcJ → e+e-J/Ψ

Ingår i Physical Review Letters, 2017.

#### Abstract

Using 4.479 x 10(8) psi(3686) events collected with the BESIII detector, we search for the decays psi(3686) -> e(+)e(-)chi(cJ) and chi(cJ) -> e(+)e(-)J/psi, where J = 0, 1, 2. The decays psi(3686) -> e(+)e(-)chi(cJ) and chi(cJ) -> e(+)e(-)J/psi are observed for the first time. The measured branching fractions are B(psi(3686) -> e(+)e(-)chi(cJ)) = (11.7 +/- 2.5 +/- 1.0) x 10(-4), (8.6 +/- 0.3 +/- 0.6) x 10(-4), (6.9 +/- 0.5 +/- 0.6) x 10(-4) for J = 0, 1, 2, and B(chi(cJ) -> e(+)e(-)J/psi) = (1.51 +/- 0.30 +/- 0.13)x10(-4), (3.73 +/- 0.09 +/- 0.25)x10(-3), (2.48 +/- 0.08 +/- 0.16)x10(-3) for J = 0, 1, 2, respectively. The ratios of the branching fractions B(psi(3686) -> e(+)e(-)chi(cJ))/B(psi(3686) -> gamma chi(cJ)) and B(chi(cJ) -> e(+)e(-)J/psi)/B(chi(cJ) -> gamma J/psi) are also reported. Also, the alpha values of helicity angular distributions of the e(+)e(-) pair are determined for psi(3686) -> e(+)e(-)chi(c1,2) and chi(c1,2) -> e(+)e(-)J/psi.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurements of cross section of e(+)e(-) -> p(p)over-bar pi(0) at center-of-mass energies between 4.008 and 4.600 GeV

Ingår i Physics Letters B, s. 45-51, 2017.

#### Abstract

Based on e(+)e(-) annihilation data samples collected with the BESIII detector at the BEPCII collider at 13 center-of-mass energies from 4.008 to 4.600 GeV, measurements of the Born cross section of e(+)e(-) -> p (p) over bar pi(0) are performed. No significant resonant structure is observed in the measured energy dependence of the cross section. The upper limit on the Born cross section of e(+)e(-) -> Y (4260) -> p (p) over bar pi(0) at the 90% C. L. is determined to be 0.01 pb. The upper limit on the ratio of the branching fractions B(Y(4260) -> p (p) over bar pi(0))/B(Y(4260) -> pi(+)pi(-) j/Psi) at the 90% C. L. is determined to be 0.02%.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Determination of the Spin and Parity of the Z(c)(3900)

Ingår i Physical Review Letters, 2017.

#### Abstract

The spin and parity of the Z(c)(3900)(+/-) state are determined to be J(P) = 1(+) with a statistical significance larger than 7 sigma over other quantum numbers in a partial wave analysis of the process e(+)e(-) -> pi(+)pi(-) J/psi We use a data sample of 1.92 fb(-1) accumulated at root s = 4.23 and 4.26 GeV with the BESIII experiment. When parametrizing the Z(c)(3900)(+/-) with a Flatte-like formula, we determine its pole mass M-pole = (3881.2 +/- 4.2(stat) +/- 52.7(syst)) MeV/c(2) and pole width Gamma(pole) = (51.8 +/- 4.6(stat) +/- 36.0(syst)) MeV. We also measure cross sections for the process e(+)e(-) -> Z(c)(3900)(+)pi(-) + c.c. -> J/psi pi(+)pi(-) and determine an upper limit at the 90% confidence level for the process e(+)e(-) -> Z(c)(4020)(+)pi(-) + c.c. -> J/psi pi(+)pi(-).

• Artikel i tidskrift

Koch, L.; Denig, A.; Drexler, P.; Garillon, B. et al.

### The Crystal Zero Degree Detector at BESIII

Ingår i Journal of Instrumentation, 2017.

#### Abstract

The BESIII experiment at the BEPCII electron positron collider at IHEP (Beijing) is collecting data in the charm-tau mass region. Electron positron collisions are a very well suited environment for the study of initial state radiation (ISR). However, the photons from ISR are strongly peaked towards small polar angles and are currently detected with limited efficiency. In order to increase the detection efficiency of ISR photons, we are developing small-size calorimeters to be placed in the very forward and backward regions. Each detector will consist of two 4 x 3 arrays of 1 x 1 x 14 cm(3) LYSO crystals. A 1 cm gap separating each of the two arrays will reduce the contamination from background at very low angles. The scintillation light will be collected by silicon photomultipliers (SiPMs). The expected event rate in the MHz range requires flash ADCs recording the preamplified SiPM outputs. The digitized waveforms will be analyzed in realtime yielding data reduction and pile-up detection. This high bandwidth data stream will be transmitted via optical fibers to FPGA-based hardware performing sub-event building, buffering, and event correlation with the BESIII trigger. The sub-events with a corresponding trigger will be sent to the BESIII event builder via TCP/IP. A single crystal equipped with a SiPM was instrumented as a prototype detector. Tests with radioactive sources were performed successfully.

• Artikel i tidskrift

Rolo, M. Da Rocha; Alexeev, M.; Amoroso, A.; Ferroli, R. Baldini et al.

### A custom readout electronics for the BESIII CGEM detector

Ingår i Journal of Instrumentation, 2017.

#### Abstract

• Artikel i tidskrift

Adolph, C.; Aghasyan, M.; Akhunzyanov, R.; Alexeev, M. G. et al.

### Final COMPASS results on the deuteron spin-dependent structure function g(1)(d) and the Bjorken sum rule

Ingår i Physics Letters B, s. 34-41, 2017.

#### Abstract

Final results are presented from the inclusive measurement of deep-inelastic polarised-muon scattering on longitudinally polarised deuterons using a 6LiD target. The data were taken at 160 GeV beam energy and the results are shown for the kinematic range 1 (GeV/c)2 < Q2 < 100 (GeV/c)2 in photon virtuality, 0.004 < x < 0.7 in the Bjorken scaling variable and W > 4GeV/c2 in the mass of the hadronic final state. The deuteron double-spin asymmetry A(1)(d) and the deuteron longitudinal-spin structure function g(1)(d) are presented in bins of x and Q2. Towards lowest accessible values of x, g(1)(d) decreases and becomes consistent with zero within uncertainties. The presented final g(1)(p) values together with the recently published final g(1)(p) values of COMPASS are used to again evaluate the Bjorken sum rule and perform the QCD fit to the g1 world data at next-to-leading order of the strong coupling constant. In both cases, changes in central values of the resulting numbers are well within statistical uncertainties. The flavour singlet axial charge a0, which is identified in the MS renormalisation scheme with the total contribution of quark helicities to the nucleon spin, is extracted at next-to-leading order accuracy from only the COMPASS deuteron data: a0(Q2 = 3 (GeV/c)2) = 0.32 +/- 0.02stat +/- 0.04syst +/- 0.05evol. Together with the recent results on the proton spin structure function g(1)(p), the results on g(1)(d) constitute the COMPASS legacy on the measurements of g1 through inclusive spin-dependent deep inelastic scattering.

Open access
• Artikel i tidskrift

Granados, Carlos; Leupold, Stefan; Perotti, Elisabetta

### The electromagnetic Sigma-to-Lambda hyperon transition form factors at low energies

Ingår i European Physical Journal A, 2017.

#### Abstract

Using dispersion theory the low-energy electromagnetic form factors for the transition of a Sigma to a Lambda hyperon are related to the pion vector form factor. The additionally required input, i.e. the two-pion-Sigma-Lambda amplitudes are determined from relativistic next-to-leading-order (NLO) baryon chiral perturbation theory including the baryons from the octet and optionally from the decuplet. Pion rescattering is again taken into account by dispersion theory. It turns out that the inclusion of decuplet baryons is not an option but a necessity to obtain reasonable results. The electric transition form factor remains very small in the whole low-energy region. The magnetic transition form factor depends strongly on one not very well determined low-energy constant of the NLO Lagrangian. One obtains reasonable predictive power if this low-energy constant is determined from a measurement of the magnetic transition radius. Such a measurement can be performed at the future Facility for Antiproton and Ion Research (FAIR).

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• Artikel i tidskrift

Clement, E.; Michelagnoli, C.; de France, G.; Li, H. J. et al.

### Conceptual design of the AGATA 1 π array at GANIL

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 1-12, 2017.

#### Abstract

The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France. This setup exploits the stable and radioactive heavy-ions beams delivered by the cyclotron accelerator complex of GANIL. Additionally, it benefits from a large palette of ancillary detectors and spectrometers to address in-beam γ-ray spectroscopy of exotic nuclei. The set-up has been designed to couple AGATA with a magnetic spectrometer, charged-particle and neutron detectors, scintillators for the detection of high-energy γ rays and other devices such as a plunger to measure nuclear lifetimes. In this paper, the design and the mechanical characteristics of the set-up are described. Based on simulations, expected performances of the AGATA l π array are presented.

• Artikel i tidskrift

Adolph, C.; Aghasyan, M.; Akhunzyanov, R.; Alexeev, M. G. et al.

### Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data

Ingår i European Physical Journal C, 2017.

#### Abstract

Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality Q(2) > 1 ( GeV/c)(2). The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised (LiD)-Li-6 target. By analysing the full range in hadron transverse momentum p(T), the different pT-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation Delta g/g is evaluated at leading order in pQCD at a hard scale of mu(2) = < Q(2) > = 3( GeV/c)(2). It is determined in three intervals of the nucleon momentum fraction carried by gluons, x(g), covering the range 0.04< x(g)< 0.28 and does not exhibit a significant dependence on xg. The average over the three intervals, < Delta g/g > = 0.113 +/- 0.038(stat) +/- 0.036( syst) at < x(g) > approximate to 0.10, suggests that the gluon polarisation is positive in the measured x(g) range.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Branching fraction measurements of psi (3686) -> gamma chi(cJ)

Ingår i Physical Review D, 2017.

#### Abstract

Using a sample of 106 million psi(3686) decays, the branching fractions of psi(3686) -> gamma chi(c0), psi(3686) -> gamma chi(c1), and psi(3686) -> gamma chi(c2) are measured with improved precision to be (9.389 +/- 0.014 +/- 0.332) %, (9.905 +/- 0.011 +/- 0.353) %, and (9.621 +/- 0.013 +/- 0.272) %, respectively, where the first uncertainties are statistical and the second ones are systematic. The product branching fractions of (psi 3686) -> gamma chi(c1), chi(c1) -> gamma J/psi (3686) -> gamma chi(c2), chi(c2) -> gamma J/psi and the branching fractions of chi(c1) -> gamma J/psi and chi(c2) -> gamma J/psi are also presented.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of higher-order multipole amplitudes in psi(3686) -> gamma chi(c1,2) with chi(c1,2) -> gamma J/psi and search for the transition eta(c)(2S) -> gamma J/psi

Ingår i Physical Review D, 2017.

#### Abstract

Using 106 x 10(6) psi(3686) events collected with the BESIII detector, we measure multipole amplitudes for the decay psi(3686) ->; gamma chi(c1,2) -> gamma gamma J/psi beyond the dominant electric-dipole amplitudes. The normalized magnetic-quadrupole (M2) amplitude for psi(3686) -> gamma chi(c1,2) -> gamma gamma J/psi and the normalized electric-dipole amplitudes for psi(3686) -> gamma chi(c2) -> gamma J/psi and determined. The M2 amplitudes for psi(3686) -> gamma chi(c1) and ; chi(c1,2) -> gamma J/psi are found to differ significantly from zero and are consistent with theoretical predictions. We also obtain the ratios of M2 contributions of psi(3686) and J/psi decays to;2,chi(c1,2,) b(2)(1/)b(2)(2) = 1.35 +/- 0.72 and a(2)(1/)a(2)(2) = 0.617 +/- 0.083,,which agree well with theoretical expectations. By considering the multipole contributions of chi(c1,2), we measure the product branching fractions for the cascade decays psi(3686) -> gamma chi(c 0,1,2) -> gamma gamma J/psi and search for the process eta(c)(2s) -> gamma J/psi through psi(3686) -> gamma eta(c)(2s).The product branching fraction for psi(3686) -> gamma chi(c0) -> gamma gamma J/psi is 3 sigma larger than published measurements, while those of psi(3686) -> gamma chi(c1,2) -> gamma gamma J/psi are consistent. No significant signal for the decay psi(3686) -> gamma eta(c) (2s) -> gamma gamma J/psi is observed, and the upper limit of the product branching fraction at the 90% confidence level is determined.

• Artikel i tidskrift

Adolph, C.; Aghasyan, M.; Akhunzyanov, R.; Alexeev, M. G. et al.

### Multiplicities of charged kaons from deep-inelastic muon scattering off an isoscalar target

Ingår i Physics Letters B, s. 133-141, 2017.

#### Abstract

Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar (LiD)-Li-6 target. They cover the kinematic domain 1 (GeV/c)(2) < Q(2) < 60 (GeV/c)(2) in the photon virtuality, 0.004 < x < 0.4, 0.1 < y < 0.7, 0.20 < z < 0.85, and W > 5 GeV/c(2) in the invariant mass of the hadronic system. The results from the sum of the z-integrated K+ and K- multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit.

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• Artikel i tidskrift

Anastasi, A.; Babusci, D.; Bencivenni, G.; Berlowski, M. et al.

### Measurement of the running of the fine structure constant below 1 GeV with the KLOE detector

Ingår i Physics Letters B, s. 485-492, 2017.

#### Abstract

We have measured the running of the effective QED coupling constant alpha(s) in the time-like region 0.6 < root s < 0.975 GeV with the KLOE detector at DA Phi NE using the Initial-State Radiation process e(+) e(-) -> mu(+) mu(-)gamma. It represents the first measurement of the running of alpha(s) in this energy region. Our results show a more than 5 sigma significance of the hadronic contribution to the running of alpha(s), which is the strongest direct evidence both in time- and space-like regions achieved in a single measurement. By using the e(+) e(-) -> pi(+) pi(-) cross section measured by KLOE, the real and imaginary parts of the shift Delta alpha(s) have been extracted. From a fit of the real part of Delta alpha(s) and assuming the lepton universality the branching ratio BR(omega -> mu(+) mu(-)) = (6.6 +/- 1.4(stat) +/- 1.7(syst)) (.) 10 (5)has been determined.

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• Artikel i tidskrift

Davies, P. J.; Grawe, H.; Moschner, K.; Blazhev, A. et al.

### The role of core excitations in the structure and decay of the 16(+) spin-gap isomer in Cd-96

Ingår i Physics Letters B, s. 474-479, 2017.

#### Abstract

The first evidence for beta-delayed proton emission from the 16(+) spin gap isomer in Cd-96 is presented. The data were obtained from the Rare Isotope Beam Factory, at the RIKEN Nishina Center, using the BigRIPS spectrometer and the EURICA decay station. beta p branching ratios for the ground state and 16(+) isomer have been extracted along with more precise lifetimes for these states and the lifetime for the ground state decay of Cd-95. Large scale shell model (LSSM) calculations have been performed and WKB estimates made for l = 0, 2, 4 proton emission from three resonance-like states in Ag-96, that are populated by the beta decay of the isomer, and the results compared to the new data. The calculations suggest that l = 2 proton emission from the resonance states, which reside similar to 5 MeV above the proton separation energy, dominates the proton decay. The results highlight the importance of core-excited wavefunction components for the 16(+) state.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurement of the absolute branching fraction for Lambda(+)(c) -> Lambda mu(+)nu(mu)

Ingår i Physics Letters B, s. 42-47, 2017.

#### Abstract

We report the first measurement of the absolute branching fraction for Lambda(+)(c) -> Lambda mu(+)nu(mu).This measurement is based on a sample of e+e(-) annihilation data produced at a center-of-mass energy root s = 4.6 GeV, collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb(-1). The branching fraction is determined to be B( Lambda(+)(c) -> Lambda mu(+)nu(mu)) = (3.49 +/- 0.46( stat) +/- 0.27( syst))%. In addition, we calculate the ratio B( Lambda(+)(c) -> Lambda mu(+)nu(mu))/B(Lambda(+)(c) -> Lambda e(+)nu(e) to be 0.96 +/- 0.16( stat) +/- 0.04( syst).

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Evidence for the singly Cabibbo suppressed decay Lambda(+)(c) -> p eta and search for Lambda(+)(c) -> p pi(0)

Ingår i Physical Review D, 2017.

#### Abstract

We study the singly Cabibbo suppressed decays Lambda(+)(c) -> p eta and Lambda(+)(c) -> p pi(0) using Lambda(+)(c)(Lambda) over bar (-)(c) pairs produced by e(+)e(-) collisions at a center-of-mass energy of root s = 4.6 GeV. The data sample was collected by the BESIII detector at the BEPCII collider and corresponds to an integrated luminosity of 567 pb(-1). We find the first evidence for the decay Lambda(+)(c) -> p eta with a statistical significance of 4.2 sigma and measure its branching fraction to be B(Lambda(+)(c) -> p eta) = (1.24 +/- 0.28(stat) +/- 0.10(sys)) x 10(-3). No significant Lambda(+)(c) -> p pi(0) signal is observed. We set an upper limit on its branching fraction B(Lambda(+)(c) -> p pi(0)) < 2.7 x 10(-4) at the 90% confidence level.

• Artikel i tidskrift

John, P. R.; Valiente-Dobon, J. J.; Mengoni, D.; Modamio, V. et al.

### In-beam gamma-ray spectroscopy of the neutron-rich platinum isotope Pt-200 toward the N=126 shell gap

Ingår i Physical Review C, 2017.

#### Abstract

The neutron-rich nucleus Pt-200 is investigated via in-beam gamma-ray spectroscopy to study the shape evolution in the neutron-rich platinum isotopes towards the N = 126 shell closure. The two-neutron transfer reaction Pt-198(Se-82, Se-80)Pt-200 is used to populate excited states of Pt-200. The Advanced Gamma Ray Tracking Array (AGATA) demonstrator coupled with the PRISMA spectrometer detects gamma rays coincident with the Se-80 recoils, the binary partner of Pt-200. The binary partner method is applied to extract the gamma-ray transitions and build the level scheme of Pt-200. The level at 1884 keV reported by Yates et al. [S. W. Yates, E. M. Baum, E. A. Henry, L. G. Mann, N. Roy, A. Aprahamian, R. A. Meyer, and R. Estep, Phys. Rev. C 37, 1889 (1988)] was confirmed to be at 1882.1 keV and assigned as the (6(1)(+)) state. An additional gamma ray was found and it presumably deexcites the (8(1)(+)) state. The results are compared with state-of-the-art beyond mean-field calculations, performed for the even-even Pt190-204 isotopes, revealing that Pt-200 marks the transition from the gamma-unstable behavior of lighter Pt nuclei towards a more spherical one when approaching the N = 126 shell closure.

• Artikel i tidskrift

Adolph, C.; Aghasyan, M.; Akhunzyanov, R.; Alexeev, G. D. et al.

### Multiplicities of charged pions and charged hadrons from deep-inelastic scattering of muons off an isoscalar target

Ingår i Physics Letters B, s. 1-10, 2017.

#### Abstract

Multiplicities of charged pions and charged hadrons produced in deep-inelastic scattering were measured in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y and the relative hadron energy z. Data were obtained by the COMPASS Collaboration using a 160 GeV muon beam and an isoscalar target ((LiD)-Li-6). They cover the kinematic domain in the photon virtuality Q(2) > 1 (GeV/c) 2, 0.004 < x < 0.4, 0.2 < z < 0.85 and 0.1 < y < 0.7. In addition, a leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Amplitude analysis of the chi(c1) -> eta pi(+)pi(-) decays

Ingår i Physical Review D, 2017.

#### Abstract

Using 448.0 x 10(6) psi(3686) events collected with the BESIII detector, an amplitude analysis is performed for psi(3686) -> gamma chi(c1), chi(c1) ->eta pi(+)pi(-) decays. The most dominant two- body structure observed is a(0)(980)(+/-) pi(-/+); a(0)(980)(+/-) -> eta pi(+/-.) line shape is modeled using a dispersion relation, and a significant nonzero a(0) (980) coupling to the eta'pi channel is measured. We observe chi(c1) -> a(2)(1700)pi production for the first time, with a significance larger than 17 sigma. The production of mesons with exotic quantum numbers, J(PC) = 1(-+), is investigated, and upper limits for the branching fractions chi(c1) -> pi(1)(1400)(+/-)pi(-/+) , chi(c1) -> pi(1)(1600)(+/-)pi(-/+) and chi(c1) -> pi 1(2015)(+/-)pi(-/+) with subsequent pi(1)(X)(+/-) -> eta pi(+/-) decay, are determined.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Evidence of Two Resonant Structures in e(+)e(-)->pi(+) pi(-) h(c)

Ingår i Physical Review Letters, 2017.

#### Abstract

The cross sections of e(+)e(-) -> pi(+) pi(-) hc at center-of-mass energies from 3.896 to 4.600 GeVare measured using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The cross sections are found to be of the same order of magnitude as those of e(+)e(-) -> pi(+) pi(-) J/psi and e(+)e(-) -> pi(+) pi(-) psi (2S), but the line shape is inconsistent with the Y states observed in the latter two modes. Two structures are observed in the e(+)e(-) -> pi(+) pi(-) hc cross sections around 4.22 and 4.39 GeV/c(2), which we call Y(4220)and Y(4390), respectively. A fit with a coherent sum of two Breit-Wigner functions results in a mass of (4218.4(- 4.5)(vertical bar 5.5) +/- 0.9) MeV/ c(2) and a width of (66.0(- 8.3)(vertical bar 12.3) +/- 0.4) MeV for the Y(4220), and a mass of (4391.5(- 6.8)(+6.3) +/- 1.0) MeV/c(2) and a width of (139.5(- 20.6)(+16.2) +/- 0.6) MeV for the Y(4390), where the first uncertainties are statistical and the second ones systematic. The statistical significance of Y(4220) and Y(4390) is 10 sigma over one structure assumption.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Precise Measurement of the e(+)e(-) ->pi(+)pi(-) J/psi Cross Section at Center-of-Mass Energies from 3.77 to 4.60 GeV

Ingår i Physical Review Letters, 2017.

#### Abstract

The cross section for the process e(+)e(-)-> pi(+) pi(-) J/psi is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using 9 fb(-1) of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of (222.0 +/- 3.1 +/- 1.4) MeV/ c(2) and a width of (44.1 +/- 4.3 +/- 2.0)MeV, while the second one has a mass of (4320.0 +/- 10.4 +/- 7.0)MeV/c(2) and a width of (101.4(- 19.7)(+25.3) +/- 10.2) MeV, where the first errors are statistical and second ones are systematic. The first resonance agrees with the Y(4260) resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in e(+)e(-)-> pi(+) pi(-) J/psi for the first time. The statistical significance of this resonance is estimated to be larger than 7.6 sigma. The mass and width of the second resonance agree with the Y(4360) resonance reported by the BABAR and Belle experiments within errors. Finally, the Y(4008) resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Determination of the number of J/psi events with inclusive J/psi decays

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2017.

#### Abstract

A measurement of the number of J/psi events collected with the BESIII detector in 2009 and 2012 is performed using inclusive decays of the J/psi. The number of J/psi events taken in 2009 is recalculated to be (223.7 +/- 1.4) x 10(6), which is in good agreement with the previous measurement, but with significantly improved precision due to improvements in the BESIII software. The number of J/psi events taken in 2012 is determined to be (1086.9 +/- 6.0) x 10(6). In total, the number of J/psi events collected with the BESIII detector is measured to be (1310.6 +/- 7.0) x 10(6), where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Study of J/ψ and ψ(3686) decay to Λ¯Λ and Σ0¯Σ0 final states

Ingår i Physical Review D, 2017.

#### Abstract

Using 1310.6 x 10(6) J/psi and 447.9 x 10(6) psi (3686) events collected with the BESIII detector at the BEPCII e(+)e(-) collider, the branching fractions and the angular distributions of J/psi and psi (3686) decays to Lambda(Lambda) over bar and Sigma(0)(Sigma) over tilde (0) final states are measured. The branching fractions are determined, with much improved precision, to be 19.43 +/- 0.03 +/- 0.33, 11.64 +/- 0.04 +/- 0.23, 3.97 +/- 0.02 +/- 0.12 and 2.44 +/- 0.03 +/- 0.11 for J/psi -> Lambda(Lambda) over bar -> Sigma(0)(Sigma) over tilde (0) , psi (3686) -> Lambda(Lambda) over bar and psi (3686) -> Sigma(0)(Sigma) over tilde (0), respectively. The polar angular distributions of psi (3686) decays are measured for the first time, while those of J/psi decays are measured with much improved precision. In addition, the ratios of branching fractions B(psi(3686)->Lambda(Lambda) over bar)/B(J/psi -> Lambda(Lambda) over bar) and B(psi(3686)->Sigma(0)(Sigma) over tilde (0))/B(J/psi ->Sigma(0)(Sigma) over tilde (0)) are determined to test the "12% rule."

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Improved measurements of branching fractions for eta(c) -> phi phi and omega phi

Ingår i Physical Review D, 2017.

#### Abstract

Using (223.7 +/- 1.4) x 10(6) J / Psi events accumulated with the BESIII detector, we study eta(c) decays to phi phi and omega phi final states. The branching fraction of n(c) -> phi phi is measured to be Br(eta(c) -> phi phi) = (2.5 +/- 0(-0.7)(+0.3) +/- 0.6) X 10(-3,) where the first uncertainty is statistical, the second is systematic, and the third is from the uncertainty of Br(J / Psi -> gamma eta(C)). No significant signal for the double Okubo-Zweig-Iizuka suppressed decay of eta(c) -> omega phi is observed, and the upper limit on the branching fraction is determined to be Br(eta(c) -> omega phi) < 2.5 x 10(-4) at the 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Amplitude Analysis of the Decays eta ' -> pi(+)pi(-)pi(0) and eta' -> pi(0)pi(0)pi(0)

Ingår i Physical Review Letters, 2017.

#### Abstract

Based on a sample of 1.31 x 10(9) J/Psi events collected with the BESIII detector, an amplitude analysis of the isospin-violating decays eta' -> pi(+)pi(-)pi(0) and eta' -> pi(0)pi(0)pi(0) is performed. A significant P-wave contribution from eta' -> rho(+/-)eta(-/+) is observed for the first time in eta' -> pi(+)pi(-)pi(0). The branching fraction is determined to be B(eta' -> rho(+/-)pi(-/+)) = (7.44 +/- 0.60 +/- 1.26 +/- 1.84) x 10(-4), where the first uncertainty is statistical, the second systematic, and the third model dependent. In addition to the nonresonant S-wave component, there is a significant sigma meson component. The branching fractions of the combined S-wave components are determined to be B(eta' -> pi(+)pi(-)pi(0))(S) = (37.63 +/- 0.77 +/- 2.22 +/- 4.48) x 10(-4) and B(eta' -> pi(0)pi(0)pi(0)) = (35.22 +/- 0.82 +/- 2.54) x 10(-4), respectively. The latter one is consistent with previous BESIII measurements.

• Artikel i tidskrift

Singh, B.; Erni, W.; Krusche, B.; Steinacher, M. et al.

### Feasibility study for the measurement of pi N transition distribution amplitudes at (P)over-barANDA in (P)over-barp -> J/psi pi(0)

Ingår i Physical Review D, 2017.

#### Abstract

The exclusive charmonium production process in (P) over barp annihilation with an associated pi 0 meson (p) over barp -> J/psi pi(0) is studied in the framework of QCD collinear factorization. The feasibility of measuring this reaction through the J/psi -> e(+) e(-) decay channel with the AntiProton ANnihilation at DArmstadt ((P) over bar ANDA) experiment is investigated. Simulations on signal reconstruction efficiency as well as the background rejection from various sources including the (P) over barp -> pi(+)pi(-)pi(0) and (p) over barp -> J/psi pi(0)pi(0) reactions are performed with PANDAROOT, the simulation and analysis software framework of the (P) over bar ANDA experiment. It is shown that the measurement can be done at (P) over bar ANDA with significant constraining power under the assumption of an integrated luminosity attainable in four to five months of data taking at the maximum design luminosity.

• Artikel i tidskrift

Adolph, C.; Akhunzyanov, R.; Alexeev, M. G.; Alexeev, G. D. et al.

### Resonance production and pi pi S-wave in pi(-) + p -> pi(-) pi(-) pi(+) + p(recoil) at 190 GeV/c

Ingår i Physical Review D, 2017.

#### Abstract

The COMPASS collaboration has collected the currently largest data set on diffractively produced pi(-) pi(-) pi(+) final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, 0.5 < m(3 pi) < 2.5 GeV/c(2), and in 11 bins of the reduced four-momentum transfer squared, 0.1 < t' < 1.0 (GeV/c)(2). This two-dimensional analysis offers sensitivity to genuine one-step resonance production, i.e. the production of a state followed by its decay, as well as to more complex dynamical effects in nonresonant 3 pi production. In this paper, we present detailed studies on selected 3p partial waves with J(PC) = 0(-+) ,1(++) ,2(-+) ,2(++) ,and 4(++). In these waves, we observe the well-known groundstate mesons as well as a new narrow axial-vector meson a(1)(1420) decaying into f(0) (980)pi. In addition, we present the results of a novel method to extract the amplitude of the pi(-)pi(+) subsystem with I(G)J(PC) = 0(+)0(++) in various partial waves from the pi(-)pi(-)pi(+) data. Evidence is found for correlation of the f (0)(980) and f(0)(1500) appearing as intermediate pi(-)pi(+) isobars in the decay of the known pi(1800) and pi(2)(1880).

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Observation of Lambda(+)(c) -> nK(S)(0)pi(+)

Ingår i Physical Review Letters, 2017.

#### Abstract

We report the first direct measurement of decays of the Lambda(+)(c) baryon involving the neutron. The analysis is performed using 567 pb(-1) of e(+)e(-) collision data collected at root s = 4.599 GeV with the BESIII detector at the BEPCII collider. We observe the decay Lambda(+)(c) -> nK(S)(0)pi(+) and measure the absolute branching fraction to be B(Lambda(+)(c) -> nK(S)(0)pi(+)) = [1.82 +/- 0.23(stat) +/- 0.11(syst)]%. A comparison to B[Lambda(+)(c) -> p( (K) over bar pi)(0)] provides an important test of isospin symmetry and final state interactions.

• Artikel i tidskrift

Adolphi, C.; Aghasyan, M.; Akhunzyanov, R.; Alexeev, M. G. et al.

### Exclusive omega meson muoproduction on transversely polarised protons

Ingår i Nuclear Physics B, s. 454-475, 2017.

#### Abstract

Exclusive production of omega mesons was studied at the COMPASS experiment by scattering 160GeV/c muons off transversely polarised protons. Five single-spin and three double-spin azimuthal asymmetries were measured in the range of photon virtuality 1(GeV/c)(2) < Q(2) < 10(GeV/c)(2), Bjorken scaling variable 0.003 < xBj < 0.3 and transverse momentum squared of the omega meson 0.05(GeV/c)(2) < p(T)(2) < 0.5(GeV/c)(2). The measured asymmetries are sensitive to the nucleon helicity-flip Generalised Parton Distributions (GPD) Et hat are related to the orbital angular momentum of quarks, the chiral-odd GPDs H-T that are related to the transversity Parton Distribution Functions, and the sign of the pi omega transition form factor. The results are compared to recent calculations of a GPD-based model.

• Artikel i tidskrift

Vogt, A.; Birkenbach, B.; Reiter, P.; Blazhev, A. et al.

### Isomers and high-spin structures in the N=81 isotones Xe-135 and Ba-137

Ingår i PHYSICAL REVIEW C, 2017.

#### Abstract

The high-spin structures and isomers of the N = 81 isotones Xe-135 and Ba-137 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe-136+ U-238 and (ii) Xe-136+ Pb-208 MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii) in the Xe-136+ Pt-198 MNT reaction employing the gamma-ray array GAMMASPHERE in combination with the gas-detector array CHICO, and (iv) via a B-11+ Te-130 fusion-evaporation reaction with the HORUS gamma-ray array at the University of Cologne. The high-spin level schemes of Xe-135 and Ba-137 are considerably extended to higher energies. The 2058-keV (19/2(-)) state in Xe-135 is identified as an isomer, closing a gap in the systematics along the N = 81 isotones. Its half-life is measured to be 9.0(9) ns, corresponding to a reduced transition probability of B(E2,19/2(-) -> 15/2(-)) = 0.52(6) W.u. The experimentally deduced reduced transition probabilities of the isomeric states are compared to shell-model predictions. Latest shell-model calculations reproduce the experimental findings generally well and provide guidance to the interpretation of the new levels.

• Artikel i tidskrift

Mach, Henryk; Korgul, A.; Gorska, M.; Grawe, H. et al.

### Ultrafast-timing lifetime measurements in Ru-94 and Pd-96: Breakdown of the seniority scheme in N=50 isotones

Ingår i PHYSICAL REVIEW C, 2017.

#### Abstract

The advanced time-delayed gamma gamma(t) method has been applied to determine half-lives of low-lying states in the N = 50 isotones Ru-94 and Pd-96. The inferred experimental E2 strengths for the 4(+) -> 2(+) transitions in the two nuclei show a dramatic deviation with respect to the shell model predictions in the (f(5/2), p, g(9/2)) proton hole space in Sn-100. The anomalous behavior can be ascribed to a breakdown of the seniority quantum number in the pi g(9/2)(n) configuration due to particle-hole excitations across the N = Z = 50 shell as confirmed by large-scale shell model calculations.

• Artikel i tidskrift

Klintefjord, M.; Ljungvall, J.; Gorgen, A.; Lenzi, S. M. et al.

### Measurement of lifetimes in Fe-62,Fe-64, Co-61,Co-63, and Mn-59

Ingår i PHYSICAL REVIEW C, 2017.

#### Abstract

Lifetimes of the 4(1)(+) states in Fe-62,Fe-64 and the 11/2(1)(-) states in Co-61,Co-63 and Mn-59 were measured at the Grand Accelerateur National d'Ions Lourds (GANIL) facility by using the Advanced Gamma Tracking Array (AGATA) and the large-acceptance variable mode spectrometer (VAMOS++). The states were populated through multinucleon transfer reactions with a U-238 beam impinging on a Ni-64 target, and lifetimes in the picosecond range were measured by using the recoil distance Doppler shift method. The data show an increase of collectivity in the iron isotopes approaching N = 40. The reduction of the subshell gap between the nu 2p(1/2) and nu 1g(9/2) orbitals leads to an increased population of the quasi-SU(3) pair (nu 1g(9/2), nu 2d(5/2)), which causes an increase in quadrupole collectivity. This is not observed for the cobalt isotopes withN < 40 for which the neutron subshell gap is larger due to the repulsive monopole component of the tensor nucleon-nucleon interaction. The extracted experimental B(E2) values are compared with large-scale shell-model calculations and with beyond-mean-field calculations with the Gogny D1S interaction. A good agreement between calculations and experimental values is found, and the results demonstrate in particular the spectroscopic quality of the Lenzi, Nowacki, Poves, and Sieja (LNPS) shell-model interaction.

Open access
• Artikel i tidskrift

Ertoprak, A.; Cederwall, B.; Jakobsson, U.; Nyako, B. M. et al.

### Lifetime Measurements With The Doppler Shift Attenuation Method Using A Thick Homogeneous Production Target — Verification of the Method

Ingår i Acta Physica Polonica B, s. 325-329, 2017.

#### Abstract

Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil ("backing") serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of gamma rays following the decay of highly excited states in the semi-magic (N = 50) nucleus Ru-94. Lifetimes of excited states in the Ru-94 nucleus have been obtained using a modified version of the LINESHAPE package from the Doppler broadened lineshapes resulting from the emission of the gamma rays, while the residual nuclei were slowing down in the thick (6 mg/cm(2)) metallic Ni-58 target. The results have been validated by comparison with a previous measurement using a different (RDDS) technique.

• Artikel i tidskrift

Siciliano, M.; Valiente-Dobon, J. J.; Goasduff, A.; Bazzacco, D. et al.

### Study Of Quadrupole Correlations In N = Z=5 0 Region Via Lifetime Measurements

Ingår i Acta Physica Polonica B, s. 331-336, 2017.

#### Abstract

During the AGATA campaign at GANIL, the neutron-deficient Sn region was populated via a multi-nucleon transfer reaction in order to directly measure the lifetime of the first excited states with a plunger device, providing complementary information to previous results obtained with Coulomb excitation experiments. The AGATA gamma-ray array was used together with the VAMOS++ spectrometer to study the nuclei of interest.

• Artikel i tidskrift

Boso, A.; Lenzi, S. M.; Recchia, F.; Bonnard, J. et al.

### Isospin Symmetry Breaking In Mirror Nuclei Mg-23-Na-23

Ingår i Acta Physica Polonica B, s. 313-318, 2017.

#### Abstract

Mirror energy differences (MED) are a direct consequence of isospin symmetry breaking. Moreover, the study of MED has proved to give valuable information of several nuclear structure properties. We present the results of an experiment performed in GANIL to study the MED in mirror nuclei Mg-23-Na-23 up to high spin. The experimental values are compared with state-of-the-art shell model calculations. This permits to enlighten several nuclear structure properties, such as the way in which the nucleons alignment proceeds, the radius variation with J, the role of the spin-orbit interaction and the importance of isospin symmetry breaking terms of nuclear origin.

• Artikel i tidskrift

Ralet, D.; Nyberg, Johan; Zielinska, M.

### Lifetime measurement of neutron-rich even-even molybdenum isotopes

Ingår i Physical Review C, 2017.

#### Abstract

Background: In the neutron-rich A≈100 mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change. Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass A=100 up to mass A=108, and the results that were obtained. Method: The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the γ ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a γ-ray transition with a known energy. This relativistic Doppler-shift-attenuation method allowed the determination of mean lifetimes from 2 to 250 ps. Results: Even-even molybdenum isotopes from mass A=100 to A=108 were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: τ=29.7+11.3−9.1 ps for the 4+ state of 108Mo and τ=3.2+0.7−0.7 ps for the 6+ state of 102Mo. Conclusions: The reduced transition strengths B(E2), calculated from lifetimes measured in this experiment, compared to beyond-mean-field calculations, indicate a gradual shape transition in the chain of molybdenum isotopes when going from A=100 to A=108 with a maximum reached at N=64. The transition probabilities decrease for 108Mo which may be related to its well-pronounced triaxial shape indicated by the calculations.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Search for eta-mesic He-4 in the dd -> (3)Hen pi(0) and dd -> (3)Hep pi(-) reactions with the WASA-at-COSY facility

Ingår i Nuclear Physics A, s. 102-115, 2017.

#### Abstract

The search for He-4-eta bound states was performed with the WASA-at-COSY facility via the measurement of the excitation function for the dd -> (3)Hen pi(0) and dd -> (3)Hep pi(-) processes. The deuteron beam momentum was varied continuously between 2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd -> He-4 eta reaction ranging from Q = 70 MeV to Q = 30 MeV. The luminosity was determined based on the dd -> (3)Hen reaction and the quasi-free proton proton scattering via dd -> ppn(spectator)n(spectator) reactions. The excitation functions, determined independently for the measured reactions, do not reveal a structure which could be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the total cross sections for the bound state production and decay in dd -> (4He-eta)(bound) -> (3)Hen pi(0) and dd -> (He-4-eta)(bound) -> (3)Hep pi(-) processes were determined taking into account the isospin relation between the both of the considered channels. The results of the analysis depend on the assumptions of the N* (1535) momentum distribution in the anticipated mesic-He-4. Assuming, as in the previous works, that this is identical with the distribution of nucleons bound with 20 MeV in He-4, we determined that (for the mesic bound state width in the range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about 3 nb and about 6 nb for n pi(0) and p pi(-) channels, respectively. However, based on the recent theoretical findings of the N*(1535) momentum distribution in the N*-He-3 nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector acceptance decreases and hence the corresponding upper limits are 5 nb and 10 nb for n pi(0) and p pi(-) channels respectively. (C) 2017 Elsevier B.V. All rights reserved.

• Artikel, forskningsöversikt

Fäldt, Göran; Wilkin, C.

### Extraction of parameters from final state interactions

Ingår i PHYSICAL REVIEW C, 2017.

#### Abstract

It is argued that final state enhancements in production reactions at large momentum transfers, such as pp -> K+ Lambda p, are primarily sensitive to the position of a virtual bound state pole in the Lambda p system rather than the Lambda p scattering length and effective range. These arguments are supported by a study of the dispersion relation derived to describe such processes as a function of the cut-off energy. This shows that the position of the virtual bound state is independent of the cut-off energy.

• Artikel i tidskrift

Kupsc, Andrzej

### Status of eta ' meson decays at BESIII

Ingår i Nuclear and Particle Physics Proceedings, s. 127-131, 2017.

#### Abstract

A sample of 1.31x10(9) J/psi events collected with the BESIII detector provides a clean source of 6.7x10(6) eta' mesons for decay studies. Some of the highlights include first observations of Dalitz decays eta' -> gamma e(+)e(-) and eta' -> omega e(+)e(-) as well as the most precise up to now studies of eta' -> pi(+)pi(-)gamma and eta' -> 3 pi dynamics.

• Artikel i tidskrift

Qvist, Staffan A.; Hellesen, Carl; Gradecka, Malwina; Dubberley, Allen E. et al.

### Tailoring the response of Autonomous Reactivity Control (ARC) systems

Ingår i Annals of Nuclear Energy, s. 383-398, 2017.

#### Abstract

The Autonomous Reactivity Control (ARC) system was developed to ensure inherent safety of Generation IV reactors while having a minimal impact on reactor performance and economic viability. In this study we present the transient response of fast reactor cores to postulated accident scenarios with and without ARC systems installed. Using a combination of analytical methods and numerical simulation, the principles of ARC system design that assure stability and avoids oscillatory behavior have been identified. A comprehensive transient analysis study for ARC-equipped cores, including a series of Unprotected Loss of Flow (ULOF) and Unprotected Loss of Heat Sink (ULOHS) simulations, were performed for Argonne National Laboratory (ANL) Advanced Burner Reactor (ABR) designs. With carefully designed ARC-systems installed in the fuel assemblies, the cores exhibit a smooth non-oscillatory transition to stabilization at acceptable temperatures following all postulated transients. To avoid oscillations in power and temperature, the reactivity introduced per degree of temperature change in the ARC system needs to be kept below a certain threshold the value of which is system dependent, the temperature span of actuation needs to be as large as possible.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurement of e(+)e(-) -> pi(+)pi(-) psi(3686) from 4.008 to 4.600 GeV and observation of a charged structure in the pi(+/-)psi(3686) mass spectrum

Ingår i Physical Review D, 2017.

#### Abstract

We study the process e(+)e(-) -> p(+)p(-)psi(3686) using 5.1 fb(-1) of data collected at 16 center-of-mass energy (root s) points from 4.008 to 4.600 GeV by the BESIII detector operating at the BEPCII collider. The measured Born cross sections for e(+)e(-) -> p(+)p(-)psi(3686) are consistent with previous results, but with much improved precision. A fit to the cross section shows contributions from two structures: the first has M = 4209.5 +/- 7.4 +/- 1.4 MeV/c(2) and Gamma = 80.1 +/- 24.6 +/- 2.9 MeV, and the second has M = 4383.8 +/- 4.2 +/- 0.8 MeV/c(2) and Gamma = 84.2 +/- 12.5 +/- 2.1 MeV, where the first errors are statistical and the second systematic. The lower-mass resonance is observed in the process e(+)e(-) -> p(+)p(-)psi(3686) for the first time with a statistical significance of 5.8 sigma. A charged charmoniumlike structure is observed in the pi(+/-)psi(3686) invariant mass spectrum for data at root s = 4.416 GeV. A fit with an S-wave Breit-Wigner function yields a mass M = 4032.1 +/- 2.4 MeV/c(2), where the errors are statistical only. However, there are still unresolved discrepancies between the fit model and data. The width of the intermediate state varies in a wide range for different kinematic regions within the data set. Therefore, no simple interpretation of the data has been found, and a future data sample with larger statistics and more theoretical input will be required to better understand this issue.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Evidence for e+e−→γηc(1S) at center-of-mass energies between 4.01 and 4.60 GeV

Ingår i Physical Review D, 2017.

#### Abstract

We present first evidence for the process e(+)e(-) -> gamma eta(c)(1S) at six center-of-mass energies between 4.01 and 4.60 GeV using data collected by the BESIII experiment operating at BEPCII. We measure the Born cross section at each energy using a combination of twelve eta(c)(1S) decay channels. We also combine all six energies under various assumptions for the energy-dependence of the cross section. If the process is assumed to proceed via the Y(4260), we measure a peak Born cross section sigma(peak)(e(+)e(-) -> gamma eta(c)(1S)) = 2.11 +/- 0.49 (stat.) +/- 0.36 (syst.) pb with a statistical significance of 4.2 sigma.

• Artikel i tidskrift

Aghasyan, M.; Akhunzyanov, R.; Alexeev, G. D.; Alexeev, M. G. et al.

### First Measurement of Transverse-Spin-Dependent Azimuthal Asymmetries in the Drell-Yan Process

Ingår i Physical Review Letters, 2017.

#### Abstract

The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/c pi(-) beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3 GeV/c(2) and 8.5 GeV/c(2). Within the experimental uncertainties, the observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of quantum chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. A recent COMPASS SIDIS measurement was obtained at a hard scale comparable to that of these DY results. This opens the way for possible tests of fundamental QCD universality predictions.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Measurement of branching fractions for psi(3686) -> gamma eta ', gamma eta, and gamma pi(0)

Ingår i Physical Review D, 2017.

#### Abstract

Using a data sample of 448 x 10(6) psi(3686) events collected with the BESIII detector operating at the BEPCII storage ring, the decays psi(3686) -> gamma eta and psi(3686) -> gamma pi(0) are observed with a statistical significance of 7.3 sigma and 6.7 sigma, respectively. The branching fractions are measured to be B(psi(3686) -> gamma eta) = (0.85 +/- 0.18 +/- 0.05) x 10(-6) and B(psi(3686) ->gamma pi(0)) = (0.95 +/- 0.16 +/- 0.05) x 10(-6). In addition, we measure the branching fraction of psi(3686) -> gamma eta' to be B(psi(3686) -> gamma eta') = (125.1 +/- 2.2 +/- 6.2)x10(-6), which represents an improvement of precision over previous results.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Amplitude analysis of D0 -> K -π+π+π-

Ingår i Physical Review D, 2017.

#### Abstract

We present an amplitude analysis of the decay D-0 -> K- pi(+)pi(+)pi(-) based on a data sample of 2.93 fb(-1) acquired by the BESIII detector at the psi(3770) resonance. With a nearly background free sample of about 16000 events, we investigate the substructure of the decay and determine the relative fractions and the phases among the different intermediate processes. Our amplitude model includes the two-body decays D-0 -> (K) over bar*(0)rho(0), D-0 -> K- a(1)(+) (1260) and D-0 -> K-1(-)(1270)pi(+), the three-body decays D-0 -> K-1(-)*(0)pi(+)pi(-) and D-0 -> K- pi(+)rho(0), as well as the four-body nonresonant decay D-0 -> K- pi(+)pi(+)pi(-). The dominant intermediate process is D-0 -> K(-)a(1)(+)(1260)accounting for a fit fraction of 54.6%.

• Artikel i tidskrift

Fäldt, Göran; Kupsc, Andrzej

### Hadronic structure functions in the e(+) e(-) -> (Lambda)over-bar Lambda reaction

Ingår i Physics Letters B, s. 16-20, 2017.

#### Abstract

Cross-section distributions are calculated for the reaction e(+)e(-) -> J/psi -> (Lambda) over bar(-> (p) over bar pi(+)) Lambda(-> p pi(-)), and related annihilation reactions mediated by vector mesons. The hyperon-decay distributions depend on a number of structure functions that are bilinear in the, possibly complex, psionic form factors G(M)(psi) and G(E)(psi) of the Lambda hyperon. The relative size and relative phase of these form factors can be uniquely determined from the unpolarized joint-decay distributions of the Lambda and anti-Lambda hyperons. Also the decay-asymmetry parameters of Lambda and anti-Lambda hyperons can be determined.

Open access
• Artikel i tidskrift

Adolph, C.; Aghasyan, M.; Akhunzyanov, R.; Alexeeva, M. G.aa et al.

### First measurement of the Sivers asymmetry for gluons using SIDIS data

Ingår i Physics Letters B, s. 854-864, 2017.

#### Abstract

The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. For quarks, it was studied in previous measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it was found to be non-zero. In this letter the evaluation of the Sivers asymmetry for gluons is presented. The contribution of the photon-gluon fusion subprocess is enhanced by requiring two high transverse-momentum hadrons. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon-gluon fusion, QCD Compton scattering and the leading-order virtual-photon absorption process. The Sivers asymmetries of the three processes are simultaneously extracted using the LEPTO event generator and a neural network approach. The method is applied to samples of events containing at least two hadrons with large transverse momentum from the COMPASS data taken with a 160 GeV/c muon beam scattered off transversely polarised deuterons and protons. With a significance of about two standard deviations, a negative value is obtained for the gluon Sivers asymmetry. The result of a similar analysis for a Collins-like asymmetry for gluons is consistent with zero. (C) 2017 The Author(s). Published by Elsevier B.V.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Observation of the decay Lambda(+)(c) -> Sigma(-)pi(+)pi(+)pi(0)

Ingår i Physics Letters B, s. 388-393, 2017.

#### Abstract

We report the first observation of the decay Lambda(+)(c) -> Sigma(-)pi(+)pi(+)pi(0), based on data obtained in e(+)e(-) annihilations with an integrated luminosity of 567 pb(-1) at vs = 4.6 GeV. The data were collected with the BESIII detector at the BEPCII storage rings. The absolute branching fraction B(Lambda(+)(c) -> Sigma(-)pi(+)pi(+)pi(0)) is determined to be (2.11 +/- 0.33(stat.) +/- 0.14(syst.))%. In addition, an improved measurement of B(Lambda(+)(c) -> Sigma(-)pi(+)pi(+)pi(0)) is determined as (1.81 +/- 0.17(stat.) +/- 0.09(syst.))%.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Search for ψ(3686)→γηc(η(1405))→γπ+π−π0

Ingår i Physical Review D, 2017.

#### Abstract

Using a sample of 448.1×106  ψ(3686) events collected with the BESIII detector, a search for the isospin violating decay ηcπ+ππ0 via ψ(3686)→γηc is presented. No signal is observed, and the upper limit on B(ψ(3686)→γηcB(ηcπ+ππ0) is determined to be 1.6×10−6 at the 90% confidence level. In addition, a search for η(1405)→f0(980)π0 in ψ(3686) radiative decays is performed. No signal is observed, and the branching fraction B(ψ(3686)→γη(1405))×B(η(1405)→f0(980)π0B(f0(980)→π+π−) is calculated to be less than 5.0×10−7 at the 90% confidence level.

• Konferensbidrag

Schönning, Karin; Li, Cui

### Future Perspectives on Baryon Form Factor Measurements with BES III

Ingår i Xiith Quark Confinement And The Hadron Spectrum, 2017.

#### Abstract

The electromagnetic structure of hadrons, parameterised in terms of electromagnetic form factors, EMFF's, provide a key to the strong interaction. Nucleon EMFF's have been studied rigorously for more than 60 years but the new techniques and larger data samples available at modern facilities have given rise to a renewed interest for the field. Recently, the access to hyperon structure by hyperon time-like EMFF provides an additional dimension. The BEijing Spectrometer (BES III) at the Beijing Electron Positron Collider (BEPC-II) in China is the only running experiment where time-like baryon EMFF's can be studied in the e(+) e(-) -> BB reaction. The BES III detector is an excellent tool for baryon form factor measurements thanks to its near 4 pi coverage, precise tracking, PID and calorimetry. All hyperons in the SU(3) spin 12 octet and spin 32 decuplet are energetically accessible within the BEPC-II energy range. Recent data on proton and Lambda hyperon form factors will be presented. Furthermore, a world-leading data sample was collected in 2014-2015 for precision measurements of baryon form factors. In particular, the data will enable a measurement of the relative phase between the electric and the magnetic form factors for Lambda and Lambda(+)(c) and hyperons. The modulus of the phase can be extracted from the hyperon polarisation, which in turn is experimentally accessible via the weak, parity violating decay. Furthermore, from the spin correlation between the outgoing hyperon and antihyperon, the sign of the phase can be extracted. This means that the time-like form factors can be completely determined for the first time. The methods will be outlined and the prospects of the BES III form factor measurements will be given. We will also present a planned upgrade

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurement of integrated luminosity and center-of-mass energy of data taken by BESIII at √s=2.125 GeV

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2017.

#### Abstract

To study the nature of the state Y (2175), a dedicated data set of e(+)e(-) collision data was collected at the center-of-mass energy of 2.125 GeV with the BESIII detector at the BEPCII collider. By analyzing large-angle Bhabha scattering events, the integrated luminosity of this data set is determined to be 108.49 +/- 0.02 +/- 0.85 pb(-1), where the first uncertainty is statistical and the second one is systematic. In addition, the center-of-mass energy of the data set is determined with radiative dimuon events to be 2126.55 +/- 0.03 +/- 0.85 MeV, where the first uncertainty is statistical and the second one is systematic.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Search for the rare decay D+ → D0e+νe

Ingår i Physical Review D, 2017.

#### Abstract

Using a data set with an integrated luminosity of 2.93 fb(-1) collected at root s = 3.773 GeV with the BESIII detector operating at the BEPCII storage rings, we search for the rare decay D+ -> D(0)e(+)nu(e). No signal events are observed. We set the upper limit on the branching fraction for D+ -> D(0)e(+)nu(e) to be 1.0 x 10(-4) at the 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Study of J/psi and psi(3686) -> Sigma(1385)(0)(Sigma)over-bar(1385)(0) and Xi(0)(Xi)over-bar(0): Study of J/ψ and ψ(3686) → (1385)0( ¯ 1385)0 and 0¯ 0

Ingår i Physics Letters B, s. 217-225, 2017.

#### Abstract

We study the decays of J/psi and psi(3686) to the final states Sigma(1385)(0)(Sigma) over bar (1385)(0) and Xi(0)(Xi) over bar (0) based on a single baryon tag method using data samples of (1310.6 +/- 7.0) x 10(6) J/psi and (447.9 +/- 2.9) x 10(6) psi(3686) events collected with the BESIII detector at the BEPCII collider. The decays to Sigma(1385)(0)(Sigma) over bar (1385)(0) are observed for the first time. The measured branching fractions of J/psi and psi(3686) to Xi(0)(Xi) over bar (0) are in good agreement with, and much more precise than, the previously published results. The angular parameters for these decays are also measured for the first time. The measured angular decay parameter for J/psi -> Sigma(1385)(0)(Sigma) over bar (1385)(0), alpha = -0.64 +/- 0.03 +/- 0.10, is found to be negative, different to the other decay processes in this measurement. In addition, the "12% rule" and isospin symmetry in the decays of J/psi and psi(3686) to Xi(Xi) over bar and Sigma(1385)(Sigma) over bar (1385) are tested.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Analysis of D+ -> (K)over-bar(0)e(+)nu(e) and D+ -> pi(0)e(+)nu(e) semileptonic decays

Ingår i Physical Review D, 2017.

#### Abstract

Using 2.93 fb(-1) of data taken at 3.773 GeV with the BESIII detector operated at the BEPCII collider, we study the semileptonic decays D+ -> (K) over bar (0)e(+)nu(e) and D+ -> pi(0)e(+)nu(e). We measure the absolute decay branching fractions B(D+ -> (K) over bar (0)e(+)nu(e)) = (8.60 +/- 0.06 +/- 0.15) x 10(-2) and B(D+ -> pi(0)e(+)nu(e)) = (3.63 +/- 0.08 +/- 0.05) x 10(-3), where the first uncertainties are statistical and the second systematic. We also measure the differential decay rates and study the form factors of these two decays. With the values of |V-cs| and |V-cd| from Particle Data Group fits assuming Cabibbo-Kobayashi-Maskawa (CKM) unitarity, we obtain the values of the form factors at q(2) = 0, f(+)(K)(0) = 0.725 +/- 0.004 +/- 0.012, and f(+)(pi)(0) = 0.622 +/- 0.012 +/- 0.003. Taking input from recent lattice QCD calculations of these form factors, we determine values of the CKM matrix elements |V-cs| = 0.944 +/- 0.005 +/- 0.015 +/- 0.024 and |V-cd| = 0.210 +/- 0.004 +/- 0.001 +/- 0.009, where the third uncertainties are theoretical.

• Artikel i tidskrift

Alfs, D.; Glowacz, B.; Moskal, P.; Zielinski, M. et al.

### Drift Chamber Calibration And Track Reconstruction In The P349 Antiproton Polarization Experiment

Ingår i Acta Physica Polonica B, s. 1983-1988, 2017.

#### Abstract

The goal of the P349 experiment is to test whether the antiproton production process can be itself a source of antiproton polarization. In this article, we present the motivation and details of the performed measurement. We report on the status of the analysis focusing mainly on calibration of the drift chambers and 3d track reconstruction.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Improved measurements of two-photon widths of the chi(cJ) states and helicity analysis for chi(c2) -> gamma gamma

Ingår i Physical Review D, 2017.

#### Abstract

Based on 448.1 x 10(6) Psi(3686) events collected with the BESIII detector, the decays Psi(3686) -> gamma chi(cJ), chi(cJ) -> gamma gamma(J = 0, 1, 2) are studied. The decay branching fractions of chi(c0,2) -> gamma gamma are measured to be B(chi(c0) -> gamma gamma) = (1.93 +/- 0.08 +/- 0.05 +/- 0.05) x 10(-4) and B(chi(c2) -> gamma gamma) = (3.10 +/- 0.09 +/- 0.07 +/- 0.11) x 10(-4) which correspond to two-photon decay widths of Gamma(gamma gamma)(chi(c0)) = 2.03 +/- 0.08 +/- 0.06 +/- 0.13 keV and Gamma(gamma gamma)(chi(c2)) = 0.60 +/- 0.02 +/- 0.01 +/- 0.04 keV with a ratio of R = Gamma(gamma gamma)(chi(c2))/Gamma(gamma gamma)(chi(c0)) = 0.295 +/- 0.014 +/- 0.007 +/- 0.027, where the uncertainties are statistical, systematic and associated with the uncertainties of B(Psi(3686) -> gamma chi(c0,2)) and the total widths Gamma(chi(c0,2)), respectively. For the forbidden decay of chi(c1) -> gamma gamma, no signal is observed, and an upper limit on the two-photon width is obtained to be Gamma(gamma gamma)(chi(c1)) < 5.3 eV at the 90% confidence level. The ratio of the two-photon widths between helicity-zero and helicity-two components in the decay chi(c2) -> gamma gamma is also measured to be f(0/2) = Gamma(lambda=0)(gamma gamma) (chi(c2))/Gamma(lambda=2)(gamma gamma) (chi(c2)) = (0.0 +/- 0.6 +/- 1.2) x 10(-2), where the uncertainties are statistical and systematic, respectively.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Branching fraction measurement of J/ψ→KSKL and search for J/ψ→KSKS

Ingår i Physical Review D, 2017.

#### Abstract

Using a sample of 1.31 x 10(9) J/Psi events collected with the BESIII detector at the BEPCII collider, we study the decays of J/Psi -> KSKL and KSKS. The branching fraction of J/Psi -> KSKL is determined to be B(J/Psi -> KSKL) = (1.93 +/- 0.01 (stat) +/- 0.05 (syst)) x 10(-4), which significantly improves on previous measurements. No clear signal is observed for the J/Psi -> KSKS process, and the upper limit at the 95% confidence level for its branching fraction is determined to be B(J/Psi -> KSKS) < 1.4 x 10(-8), which improves on the previous searches by 2 orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.

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Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Search for the rare decays J/ψ→D0e+e−+c.c. and ψ(3686)→D0e+e−+c.c.

Ingår i Physical Review D, 2017.

#### Abstract

Using the data samples of (1310.6 +/- 7.2) x 10(6) J/psi events and (448.1 +/- 2.9) x 10(6) psi(3686) events collected with the BESIII detector, we search for the rare decays J/psi -> D(0)e(+) e(-) + c.c. and psi(3686) -> D(0)e(+) e(-) + c.c. No significant signals are observed and the corresponding upper limits on the branching fractions at the 90% confidence level are determined to be B(J/psi -> D(0)e(+) e(-) + c.c.) < 8.5 x 10(-8) and B(psi(3686) -> D(0)e(+) e(-) + c.c.) < 1.4 x 10(-7), respectively. Our limit on B(J/psi -> D(0)e(+) e(-) + c.c.) is more stringent by 2 orders of magnitude than the previous results, and B(psi(3686) -> D(0)e(+) e(-) + c.c.) is measured for the first time.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Observation of the helicity-selection-rule suppressed decay of the χc2 charmonium state

Ingår i Physical Review D, 2017.

#### Abstract

The decays of chi(c2) -> K+K- pi(0), KSK +/-pi(-/+), and pi(+)pi(-)pi(0) are studied with the psi(3686) data samples collected with the Beijing Spectrometer ( BESIII). For the first time, the branching fractions of chi(c2) -> K*(K) over bar,chi(c2) -> a(2)(+/-)(1320)pi(-/+)/a(2)(0)(1320)pi(0), and chi(c2) -> rho(770)(+/-)pi(-/+) are measured. Here, K*(K) over bar denotes both K*K-+/-(-/+) and its isospin-conjugated process K*(0)(K) over bar (0) + c: c:, and K* denotes the resonances K*(892), K*(2)(1430), and K*(3)(1780). The observations indicate a strong violation of the helicity selection rule in chi(c2) decays into vector and pseudoscalar meson pairs. The measured branching fractions of chi(c2) -> K*(892)(K) over bar are more than ten times larger than the upper limit of chi(c2) -> rho(770)(+/-)pi(-/+), which is so far the first direct observation of a significant U-spin symmetry breaking effect in charmonium decays.

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• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Isoscalar single-pion production in the region of Roper and d*(2380) resonances

Ingår i Physics Letters B, s. 599-607, 2017.

#### Abstract

Exclusive measurements of the quasi-free pn -> pp pi(-) and pp -> pp pi(0) reactions have been performed by means of pd collisions at T-p= 1.2 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region T-p= 0.95-1.3 GeV (root s = 2.3-2.46 GeV), which includes the regions of triangle(1232), N*(1440) and d*(2380) resonance excitations. From these measurements the isoscalar single-pion production has been extracted, for which data existed so far only below T-p = 1 GeV. We observe a substantial increase of this cross section around 1 GeV, which can be related to the Roper resonance N*(1440), the strength of which shows up isolated from the triangle resonance in the isoscalar (N pi)(I=0) invariant-mass spectrum. No evidence for a decay of the dibaryon resonance d*(2380) into the isoscalar (NN pi)(I=0) channel is found. An upper limit of 180 mu b (90% CL.) corresponding to a branching ratio of 9% has been deduced.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Dark photon search in the mass range between 1.5 and 3.4 GeV/c

Ingår i Physics Letters B, s. 252-257, 2017.

#### Abstract

Using a data set of 2.93 fb taken at a center-of-mass energy root s = 3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a dark photon. We examine the initial state radiation reactions e(+)e(-) -> e(+)e(-) gamma(ISR) and e(+)e(-) -> mu(+)mu(-) gamma(ISR) for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/c(2) and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurement of cross sections of the interactions e(+)e(-) -> phi phi omega and e(+)e(-) -> phi phi phi at center-of-mass energies from 4.008 to 4.600 GeV

Ingår i Physics Letters B, s. 78-86, 2017.

#### Abstract

Using data samples collected with the BESIII detector at the BEPCII collider at six center-of-mass energies between 4.008 and 4.600 GeV, we observe the processes e(+)e(-) -> phi phi omega and e(-)e(-) -> phi phi phi. The Born cross sections are measured and the ratio of the cross sections sigma(e(+)e(-) -> phi phi omega)/sigma(e(-)e(-) -> phi phi phi) is estimated to be 1.75 +/- 0.22 +/- 0.19 averaged over six energy points, where the first uncertainty is statistical and the second is systematic. The results represent first measurements of these interactions.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Search for the radiative leptonic decay D+ -> gamma e (+) nu(e)

Ingår i Physical Review D, 2017.

#### Abstract

Using an electron-positron collision data sample of 2.93 fb(-1) collected at a center-of-mass energy of root s = 3.773 GeV with the BESIII detector, we present the first search for the radiative leptonic decay D+ -> gamma e(+)nu(e). The analysis is performed with a double-tag method. We do not observe a significant D+ -> gamma e(+)nu(e) signal, and obtain an upper limit on the branching fraction of D+ -> gamma e(+)nu(e) decay with the energy of radiative photon larger than 10 MeV of 3.0 x 10(-5) at the 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Observation of e(+)e(-) -> eta h(c) at center-of-mass energies from 4.085 to 4.600 GeV

Ingår i Physical Review D, 2017.

#### Abstract

We observe for the first time the process e(+) e(-) -> eta h(c) with data collected by the BESIII experiment. Significant signals are observed at the center-of-mass energy root s = 4.226 GeV, and the Born cross section is measured to be (9.5(-2.0)(+2.2)) pb. Evidence for eta h(c) is observed at root s = 4.358 GeV with a Born cross section of (10.0(-2.7)(+3.1)) pb, and upper limits on the production cross section at other center-of-mass energies between 4.085 and 4.600 GeV are determined.

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Adolph, C.; Aghasyan, M.; Akhunzyanov, R.; Alexeev, M. G. et al.

### Sivers asymmetry extracted in SIDIS at the hard scales of the Drell-Yan process at COMPASS

Ingår i Physics Letters B, s. 138-145, 2017.

#### Abstract

Eight proton transverse-spin-dependent azimuthal asymmetries are extracted in four regions of the photon virtuality Q(2) from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon nucleon scattering. These Q(2) regions correspond to the four regions of the di-muon mass root Q(2) used in the ongoing analyses of the COMPASS Drell-Yan measurements, which allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. In addition, for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function various two-dimensional kinematic dependences are presented. The integrated Sivers asymmetries are found to be positive with an accutacy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurements of the branching fractions for D+ -> (KSKSK+)-K-0-K-0+, (KSKS0)-K-0 pi + and D-0 -> (KSKS0)-K-0, (KSKSKS0)-K-0-K-0

Ingår i Physics Letters B, s. 231-237, 2017.

#### Abstract

By analyzing 2.93 fb(-1) of data taken at the psi(3770) resonance peak with the BESIII detector, we measure the branching fractions for the hadronic decays D+ -> (KSKSK+)-K-0-K-0, D+ -> (KSKS0)-K-0 pi(+), D-0 -> (KSKS0)-K-0 and D-0 -> (KSKSKS0)-K-0-K-0.They are determined to be B(D+ -> (KSKSK+)-K-0-K-0) = (2.54 +/- 0.05(stat.) +/- 0.12(sys.))x 10(-3), B(D+ -> (KSKS0)-K-0 pi(+)) = (2.70 +/- 0.05(stat,) +/- 0.12(sys.)) x 10(-3), B(D+ -> (KSKS0)-K-0) = (1.67 +/- 0.11(stat.) +/- 0.11(sys.)) x 10(-4) and B(D+ -> (KSKSKS0)-K-0-K-0) = (7.21 +/- 0.33(stat.) +/- 0.44(sys,)) x 10(-4), where the second one is measured for the first time and the others are measured with significantly improved precision over the previous measurements.

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• Artikel i tidskrift

Fäldt, Göran; Wilkin, C.

### Comparison of the pp → π+pn and pp → π+d production rates

Ingår i Physics Letters B, s. 146-148, 2017.

#### Abstract

Fully constrained bubble chamber data on the pp -> pi(+)pn and pp -> pi(+)d reactions are used to investigate the ratio of the counting rates for the two processes at low pn excitation energies. Whereas the ratio is in tolerable agreement with that found in a high resolution spectrometer experiment, the angular distribution in the final pn rest frame shows that the deviation from the predictions of final state interaction theory must originate primarily from higher partial waves in the pn system. These considerations might also be significant for the determination of the S -wave Ap scattering length from data on the pp -> K+Lambda p reaction.

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• Artikel i tidskrift

Hanhart, C.; Holz, S.; Kubis, B.; Kupść, Andrzej et al.

### The branching ratio omega -> pi(+) pi(-) revisited

Ingår i European Physical Journal C, 2017.

#### Abstract

We analyze themost recent data for the pion vector form factor in the timelike region, employing a modelindependent approach based on dispersion theory. We confirm earlier observations about the inconsistency of different modern high-precision data sets. Excluding the BaBar data, we find an updated value for the isospin-violating branching ratio B(omega -> pi(+) pi(-)) = (1.46 +/- 0.08) x 10(-2). As a side result, we also extract an improved value for the pion vector or charge radius, root < r(V)(2)> = 0.6603(5)(4) fm, where the first uncertainty is statistical as derived from the fit, while the second estimates the possible size of nonuniversal radiative corrections. In addition, we demonstrate that modern high-quality data for the decay. eta'-> pi(+) pi(-) will allow for an even improved determination of the transition strength omega -> pi(+) pi(-).

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• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Measurement of the ω → π+π−π0 Dalitz plot distribution: The WASA-at-COSY Collaboration

Ingår i Physics Letters B, s. 418-425, 2017.

#### Abstract

Using the production reactions pd -> He-3 omega and pp -> pp omega, the Dalitz plot distribution for the omega -> pi(+)pi(-)pi(0)decay is studied with the WASA detector at COSY, based on a combined data sample of (4.408 +/- 0.042) x 10(4) events. The Dalitz plot density is parametrised by a product of the P-wave phase space and a polynomial expansion in the normalised polar Dalitz plot variables Z and phi. For the first time, a deviation from pure P-wave phase space is observed with a significance of 4.1 sigma. The deviation is parametrised by a linear term 1+2 alpha Z, with alpha determined to be +0.147 +/- 0.036, consistent with the expectations of rho-meson-type final-state interactions of the P-wave pion pairs. (C) 2017 The Author. Published by Elsevier B.V.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Study of J/ψ and ψ(3686) decays to π+π−η′

Ingår i Physical Review D, 2017.

#### Abstract

Using the data samples of 1.31×109  J/ψ events and 4.48×108  ψ(3686) events collected with the BESIII detector, partial wave analyses on the decays J/ψ and ψ(3686)→π+π−η′ are performed with a relativistic covariant tensor amplitude approach. The dominant contribution is found to be J/ψ and ψ(3686) decays to ρη′. In the J/ψ decay, the branching fraction B(J/ψ→ρη′) is determined to be (7.90±0.19(stat)±0.49(sys))×10−5. Two solutions are found in the ψ(3686) decay, and the corresponding branching fraction B(ψ(3686)→ρη′) is (1.02±0.11(stat)±0.24(sys))×10−5 for the case of destructive interference, and (5.69±1.28(stat)±2.36(sys))×10−6 for constructive interference. As a consequence, the ratios of branching fractions between ψ(3686) and J/ψ decays to ρη′ are calculated to be (12.9±1.4(stat)±3.1(sys))% and (7.2±1.6(stat)±3.0(sys))%, respectively. We also determine the inclusive branching fractions of J/ψ and ψ(3686) decays to π+π−η′ to be (1.36±0.02(stat)±0.08(sys))×10−4 and (1.51±0.14(stat)±0.23(sys))×10−5, respectively

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M. et al.

### Observation of χc2→η′η′ and χc0,2→ηη′

Ingår i Physical Review D, 2017.

#### Abstract

Using a sample of 448.1×106 ψ(3686) events collected with the BESIII detector in 2009 and 2012, we study the decays χc0,2η′η′ and ηη′. The decays χc2η′η′, χc0ηη′ and χc2ηη′ are observed for the first time with statistical significances of 9.6σ, 13.4σ and 7.5σ, respectively. The branching fractions are determined to be Bc0η′η′)=(2.19±0.03±0.14)×10−3, Bc2η′η′)=(4.76±0.56±0.38)×10−5, Bc0ηη′)=(8.92±0.84±0.65)×10−5 and B(χc2→ηη′)=(2.27±0.43±0.25)×10−5, where the first uncertainties are statistical and the second are systematic. The precision for the measurement of Bc0η′η′) is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for χc0,2 decays into pseudoscalar meson pairs can be clarified.

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Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Improved measurement of the absolute branching fraction of D+ -> (K)over-bar(0)mu(+)nu(mu)

Ingår i European Physical Journal C, 2016.

#### Abstract

By analyzing 2.93 fb(-1) of data collected at root s = 3.773 GeV with the BESIII detector, we measure the absolute branching fraction B(D+ -> (K) over bar (0) (+)(mu)nu(mu)) = (8.72 +/- 0.07(stat). +/- 0.18(sys).) %, which is consistent with previous measurements within uncertainties but with significantly improved precision. Combining the Particle Data Group values of B(D-0 -> K- mu(+)nu(mu)), B(D+-> (K) over bar (0)e(+)nu(e)), and the lifetimes of the D-0 and D+ mesons with the value of B(D+ -> (K) over bar (0)mu(+)nu(mu)) measured in this work, we determine the following ratios of partial widths: Gamma (D-0 -> (K) over bar (-)mu(+)nu(mu))/Gamma (D+ -> (K) over bar (0)mu+nu(mu)) = 0.963 +/- 0.044 and Gamma (D+ -> (K) over bar (0) mu+nu(mu))/Gamma(D+ -> (K) over bar (0)e+nu(e)) = 0.988 +/- 0.033.

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• Artikel i tidskrift

Vogt, A.; Birkenbach, B.; Reiter, P.; Blazhev, A. et al.

### High-spin structure of Xe-134

Ingår i PHYSICAL REVIEW C, 2016.

#### Abstract

Detailed spectroscopic information on the N similar to 82 nuclei is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in Xe-134 is investigated after multinucleon transfer (MNT) and actinide fission. Xenon-134 was populated as (i) a transfer product in Xe-136 + U-238 and Xe-136 + Pb-208 MNT reactions and (ii) as a fission product in the Xe-136 + U-238 reaction employing the high-resolution Advanced Gamma Tracking Array (AGATA). Trajectory reconstruction has been applied for the complete identification of beamlike transfer products with the magnetic spectrometer PRISMA. The Xe-136 + Pt-198 MNT reaction was studied with the gamma-ray spectrometer GAMMASPHERE in combination with the gas detector array Compact Heavy Ion Counter (CHICO). Several high-spin states in Xe-134 on top of the two long-lived isomers are discovered based on gamma gamma-coincidence relationships and information on the gamma-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of Xe-134 is extended up to an

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Search for an isospin I=3 dibaryon

Ingår i Physics Letters B, s. 455-461, 2016.

#### Abstract

Various theoretical calculations based on QCD or hadronic interactions predict that in addition to the recently observed dibaryon resonance d*(2380) with I(J(P)) = 3(0(+)) there should also exist a dibaryon resonance with mirrored quantum numbers I(J(P)) = 3(0(+)). We report here on a search for such a NN-decoupled state in data on the pp -> pp pi(+) pi(+) pi(-) pi(-) reaction. Since no clear-cut evidence has been found, we give upper limits for the production cross section of such a resonance in the mass range 2280-2500 MeV.

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Aaboud, M.; Bergeaas Kuutmann, Elin; Brenner, Richard; Ekelöf, Tord et al.

### Search for bottom squark pair production in proton-proton collisions at root s=13 TeV with the ATLAS detector

Ingår i European Physical Journal C, 2016.

#### Abstract

The result of a search for pair production of the supersymmetric partner of the Standard Model bottom quark ((b) over tilde (1)) is reported. The search uses 3.2 fb(-1) of pp collisions at root s = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2015. Bottom squarks are searched for in events containing large missing transverse momentum and exactly two jets identified as originating from b-quarks. No excess above the expected Standard Model background yield is observed. Exclusion limits at 95 % confidence level on the mass of the bottom squark are derived in phenomenological supersymmetric R-parity-conserving models in which the (b) over tilde (1) is the lightest squark and is assumed to decay exclusively via (b) over tilde (1) -> b (chi) over tilde (0)(1), where (chi) over tilde (0)(1) is the lightest neutralino. The limits significantly extend previous results; bottom squark masses up to 800 (840) GeV are excluded for the. (chi) over tilde (0)(1) mass below 360 (100) GeV whilst differences in mass above 100 GeV between the (b) over tilde (1) and the (chi) over tilde (0)(1) are excluded up to a (b) over tilde (1) mass of 500 GeV.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the leptonic decay width of J/psi using initial state radiation

Ingår i Physics Letters B, s. 98-103, 2016.

#### Abstract

Using a data set of 2.93 fb(-1) taken at a center-of-mass energy of root s = 3.773 GeV with the BESIII detector at the BEPCII collider, we measure the process e(+) e(-) -> J/psi gamma -> mu(+)mu(-)gamma and determine the product of the branching fraction and the electronic width B-mu mu . Gamma(ee) = (333.4 +/- 2.5(stat) +/- 4.4(sys)) eV. Using the earlier-published BESIII result for B-mu mu = (5.973 +/- 0.007(stat) +/- 0.037(sys))%, we derive the J/psi electronic width Gamma(ee) = (5.58 +/- 0.05(stat) +/- 0.08(sys)) keV. (C) 2016 The Author(s). Published by Elsevier B.V.

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• Artikel i tidskrift

Singh, B.; Erni, W.; Krusche, B.; Steinacher, M. et al.

### Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR

Ingår i European Physical Journal A, 2016.

#### Abstract

Simulation results for future measurements of electromagnetic proton form factors at PANDA (FAIR) within the PandaRoot software framework are reported. The statistical precision with which the proton form factors can be determined is estimated. The signal channel (p) over barp -> e(+)e(-) is studied on the basis of two different but consistent procedures. The suppression of the main background channel, i.e. (p) over barp -> pi(+)pi(-), is studied. Furthermore, the background versus signal efficiency, statistical and systematical uncertainties on the extracted proton form factors are evaluated using two different procedures. The results are consistent with those of a previous simulation study using an older, simplified framework. However, a slightly better precision is achieved in the PandaRoot study in a large range of momentum transfer, assuming the nominal beam conditions and detector performance.

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• Artikel i tidskrift

Aartsen, M. G.; Abraham, K.; Ackermann, M.; Adams, J. et al.

### Searches for Sterile Neutrinos with the IceCube Detector

Ingår i Physical Review Letters, 2016.

#### Abstract

The IceCube neutrino telescope at the South Pole has measured the atmospheric muon neutrino spectrum as a function of zenith angle and energy in the approximate 320 GeV to 20 TeV range, to search for the oscillation signatures of light sterile neutrinos. No evidence for anomalous nu(mu) or (nu) over bar (mu) disappearance is observed in either of two independently developed analyses, each using one year of atmospheric neutrino data. New exclusion limits are placed on the parameter space of the 3 + 1 model, in which muon antineutrinos experience a strong Mikheyev-Smirnov-Wolfenstein-resonant oscillation. The exclusion limits extend to sin(2)2 theta(24) <= 0.02 at Delta m(2) similar to 0.3 eV(2) at the 90% confidence level. The allowed region from global analysis of appearance experiments, including LSND and MiniBooNE, is excluded at approximately the 99% confidence level for the global best-fit value of vertical bar U-e4 vertical bar(2).

• Artikel i tidskrift

Ablikim, M.; Achasov, N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the absolute branching fraction of D+ → K̅0 e+νe via K̅0 → π 0 π 0

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2016.

#### Abstract

By analyzing 2.93 fb(-1) data collected at the center-of-mass energy root s = 3.773 GeV with the BESIII detector, we measure the absolute branching fraction of the semileptonic decay D+ -> (K) over bar (0)e(+)nu(e) to be B(D (+) -> (K) over bar (0)e(+)nu(e)) = (8.59 +/- 0.14 +/- 0.21)% using (K) over bar (0) -> K-S(0) -> pi(0) pi(0), where the first uncertainty is statistical and the second systematic. Our result is consistent with previous measurements within uncertainties..

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• Artikel i tidskrift

Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M. et al.

### Measurement of the top quark mass using the matrix element technique in dilepton final states

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

We present a measurement of the top quark mass in p (p) over bar collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The data were collected by the D0 experiment corresponding to an integrated luminosity of 9.7 fb(-1). The matrix element technique is applied to t (t) over bar events in the final state containing leptons (electrons or muons) with high transverse momenta and at least two jets. The calibration of the jet energy scale determined in the lepton + jets final state of t (t) over bar decays is applied to jet energies. This correction provides a substantial reduction in systematic uncertainties. We obtain a top quark mass of m(t) = 173.93 +/- 1.84 GeV.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of D+ -> K-pi(+)e(+)nu(e)

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

We present an analysis of the decay D+ -> K-pi(+)e(+)nu(e) based on data collected by the BESIII experiment at the psi(3770) resonance. Using a nearly background-free sample of 18262 events, we measure the branching fraction B(D+ -> K-pi+e+nu e) = (3.77 +/- 0.03 +/- 0.08)%. For 0.8 < m(K pi) < 1.0 GeV/c(2), the partial branching fraction is B(D+ -> K-pi+e+nu e)([0.8,1.0]) = (3.39 +/- 0.03 +/- 0.08)%. A partial wave analysis shows that the dominant (K) over bar* (892)degrees component is accompanied by an S-wave contribution accounting for (6.05 +/- 0.22 +/- 0.18)% of the total rate and that other components are negligible. The parameters of the (K) over bar* (892)degrees resonance and of the form factors based on the spectroscopic pole dominance predictions are also measured. We also present a measurement of the (K) over bar* (892)degrees helicity basis form factors in a model-independent way.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Measurements of branching ratios for eta decays into charged particles

Ingår i PHYSICAL REVIEW C, 2016.

#### Abstract

The WASA-at-COSY experiment has collected 3 x 10(7) events with eta mesons produced via the reaction pd -> He-3 eta at T = 1.0 GeV. Using this data set, we evaluate the branching ratios of the decays eta -> pi(+)pi(-)gamma, eta -> e(+)e(-)gamma, eta -> pi(+)pi(-)e(+)e(-), and eta -> e(+)e(-)e(+)e(-). The branching ratios are normalized to the eta -> pi(+)pi(-) pi(0) decay. In addition an upper limit on a CP-violating asymmetry in eta -> pi(+)pi(-)e(+)e(-) is extracted.

• Konferensbidrag

Papenbrock, Michael

### Antihyperon-Hyperon production in antiproton-proton annihilations with PANDA at FAIR

Ingår i 21st International Conference On Few-Body Problems In Physics, 2016.

#### Abstract

Hyperon production is an excellent probe of QCD in the confinement domain, and spin observables are a powerful tool in understanding the underlying physics. For the Omega hyperon, seven polarisation parameters can be extracted from the angular distributions of its decay products with the future PANDA experiment at FAIR. Simulation studies reveal great prospects for strange and single charmed hyperon channels with PANDA. Software tools supporting these investigations are currently under development.

Open access
• Artikel i tidskrift

Aad, G.; Bergeås, Elin Kuutmann; Brenner, Richard; Ekelöf, Tord et al.

### The performance of the jet trigger for the ATLAS detector during 2011 data taking

Ingår i European Physical Journal C, 2016.

#### Abstract

The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton-proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon-nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accepted by the trigger if they contain one or more jets above some transverse energy threshold. During 2011 data taking the jet trigger was fully efficient for jets with transverse energy above 25 GeV for triggers seeded randomly at Level 1. For triggers which require a jet to be identified at each of the three trigger levels, full efficiency is reached for offline jets with transverse energy above 60 GeV. Jets reconstructed in the final trigger level and corresponding to offline jets with transverse energy greater than 60 GeV, are reconstructed with a resolution in transverse energy with respect to offline jets, of better than 4 % in the central region and better than 2.5 % in the forward direction.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the Ds<(+)-> l(+)ve branching fractions and the decay constant fDs+

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

Using 482 pb(-1) of e(+) e(-) collision data collected at a center-of-mass energy of root s = 4.009 GeV with the BESIII detector, we measure the branching fractions of the decays D-s(+) -> u(+)v(u) and D-s(+) -> tau(+)v(tau). By constraining the ratio of decay rates of Ds(+) to tau(+)v(u) and to u(+)v(u) to the Standard Model prediction, the branching fractions are determined to be B(D-s(+) -> u(+)v(u) = (0.495 +/- 0.067 +/- 0.026)% and B(D-s(+) -> tau(+)v(tau) = (4.83 +/- 0.65 +/- 0.26)% Using these branching fractions, we obtain a value for the decay constant f(Ds+) of (241.0 +/- 16.3 +/- 6.5) MeV, where the first error is statistical and the second systematic.

• Konferensbidrag

Alfs, D.; Asaturyan, A.; Carmignotto, M.; Diermaier, M. et al.

### Status of the analysis for the search of polarization in the antiproton production process

Ingår i MESON 2016 - 14th International Workshop On Meson Production, Properties And Interaction, 2016.

#### Abstract

The P-349 experiment aims to test whether for antiprotons the production process itself can be a source of polarization in view of the preparation of a polarized antiproton beam. In this article we present the details of performed measurements and report on the status of the ongoing analysis.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Observation of e(+)e(-) -> eta ' J/psi center-of-mass energies between 4.189 and 4.600 GeV

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

The process e(+)e(-) -> eta' J/psi is observed for the first time with a statistical significance of 8.6 sigma at center-of-mass energy root s = 4.226 GeV and 7.3 sigma at root s = 4.258 GeV using data samples collected with the BESIII detector. The Born cross sections are measured to be (3.7 +/- 0.7 +/- 0.3) and (3.9 +/- 0.8 +/- 0.3) pb at root s = 4.226 and 4.258 GeV, respectively, where the first errors are statistical and the second systematic. Upper limits at the 90% confidence level of the Born cross sections are also reported at other 12 energy points.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Observation of J/psi -> gamma eta pi(0)

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

We present the first study of the process J/psi -> gamma eta pi(0) using (223.7 +/- 1.4) x 10(6) J/psi events accumulated with the BESIII detector at the BEPCII facility. The branching fraction for J/psi -> gamma eta pi(0) is measured to be B(J/psi -> gamma eta pi(0)) = (2.14 +/- 0.18(stat) +/- 0.25(syst)) x 10(-5). With a Bayesian approach, the upper limits of the branching fractions B(J/psi -> gamma a(0)(980), a(0)(980) -> eta pi(0)) and B(J/psi -> gamma a(2)(1320), a(2)(1320) -> eta pi(0)) are determined to be 2.5 x 10(-6) and 6.6 x 10(-6) at the 95% confidence level, respectively. All of these measurements are given for the first time.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurements of the absolute branching fractions for D-s(+) -> eta e(+)nu(e) and D-s(+) -> eta ' e(+)nu(e)

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

By analyzing 482 pb(-1) of e(+)e(-) collision data collected at root s = 4.009 GeV with the BESIII detector at the BEPCII collider, we measure the absolute branching fractions for the semileptonic decays D-s(+) -> eta e(+)nu(e) and D-s(+) -> eta ' e(+)nu(e) to be B(D-s(+) -> eta e(+)nu(e)) = (2.30 +/- 0.31 +/- 0.08)% and B(D-s(+) -> eta ' e(+)nu(e)) = (0.93 +/- 0.30 +/- 0.05)%, respectively, and their ratio B(D-s(+) -> eta ' e(+)nu(e)) / B(D-s(+) -> eta ' e(+)nu(e)) = 0.40 +/- 0.14 +/- 0.02, where the first uncertainties are statistical and the second ones are systematic. The results are in good agreement with previous measurements within uncertainties; they can be used to determine the eta-eta' mixing angle and improve upon the D-s(+) semileptonic branching ratio precision.

• Artikel i tidskrift

Fäldt, Göran

### Polarization observables in the e+e- ->(Lambda)over-bar Lambda reaction

Ingår i European Physical Journal A, 2016.

#### Abstract

Cross-section, vector-polarization, and tensor-polarization distributions are calculated for the reactions e(+)e(-) -> (p) over barp and e(+)e(-) ->(Lambda) over bar Lambda . Each reaction requires six characteristic functions that are bilinear in the, possibly complex, electromagnetic Form factors, denoted G(E)(P-2) and G(M) (P-2), of p and A. For the hyperon reaction also the joint-decay distributions of A and A are calculated. Their knowledge allows a complete determination of the hyperon electromagnetic form factors, without measuring hyperon spins. We explain how this is done in practice. For some tensor-polarization components our results are in conflict with previously repeatedly published distributions.

• Konferensbidrag

Paradela, C.; Duran, I.; Tassan-Got, L.; Audouin, L. et al.

### High accuracy 235U(n,f) data in the resonance energy region

2016.

#### Abstract

The U-235 neutron-induced cross section is widely used as reference cross section for measuring other fission cross sections, but in the resonance region it is not considered as an IAEA standard because of the scarce experimental data covering the full region. In this work, we deal with a new analysis of the experimental data obtained with a detection setup based on parallel plate ionization chambers (PPACs) at the CERN n_TOF facility in the range from 1 eV to 10 keV. The relative cross section has been normalised to the IAEA value in the region between 7.8 and 11 eV, which is claimed as well-known. Comparison with the ENDF/B-VII evaluation and the IAEA reference file from 100 eV to 10 keV are provided.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Amplitude analysis of the π$^0$π$^0$ system produced in radiative J/ψ decays

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

An amplitude analysis of the π0π0 system produced in radiative J/ψ decays is presented. In particular, a piecewise function that describes the dynamics of the π0π0 system is determined as a function of Mπ0π0 from an analysis of the (1.311±0.011)×109 J/ψ decays collected by the BESIII detector. The goal of this analysis is to provide a description of the scalar and tensor components of the π0π0 system while making minimal assumptions about the properties or number of poles in the amplitude. Such a model-independent description allows one to integrate these results with other related results from complementary reactions in the development of phenomenological models, which can then be used to directly fit experimental data to obtain parameters of interest. The branching fraction of J/ψ→γπ0π0 is determined to be (1.15±0.05)×10-3, where the uncertainty is systematic only and the statistical uncertainty is negligible.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Precision measurement of the $D^{*0}$ decay branching fractions

Ingår i PHYSICAL REVIEW D, 2016.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of J/Psi -> p(p)over-bar phi at BESIII

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

Using a data sample of 1.31×109 J/ψ events accumulated with the BESIII detector, the decay J/ψ→pp¯ϕ is studied via two decay modes, ϕ→KS0KL0 and ϕ→K+K-. The branching fraction of J/ψ→pp¯ϕ is measured to be B(J/ψ→pp¯ϕ)=[5.23±0.06(stat)±0.33(syst)]×10-5, which agrees well with a previously published measurement, but with a significantly improved precision. No evident enhancement near the pp¯ mass threshold, denoted as X(pp¯), is observed, and the upper limit on the branching fraction of J/ψ→X(pp¯)ϕ→pp¯ϕ is determined to be B(J/ψ→X(pp¯)ϕ→pp¯ϕ)<2.1×10-7 at the 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of psi decays to the Xi(-)(Xi)over-bar(+) and Sigma(1385)(-/+)(Sigma)over-bar(1385)(+/-) final states

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

We study the decays of the charmonium resonances J/psi and psi(3686) to the final states Xi(-)(Xi) over bar (+), S(1385)(-/+)(Sigma) over bar (1385)(+/-) based on a single baryon tag method using data samples of (223.7 +/- 1.4) x 10(6) J/psi and (106.4 +/- 0.9) x 10(6) psi(3686) events collected with the BESIII detector at the BEPCII collider. The decay psi(3686) -> Sigma(1385)(-/+)(Sigma) over bar (1385)(+/-) is observed for the first time, and the measurements of the other processes, including the branching fractions and angular distributions, are in good agreement with, and much more precise than, the previously published results. Additionally, the ratios B(psi(3686)->Xi(-)(Xi) over bar (+))/B(J/psi ->Xi(-)(Xi) over bar (+)), B(psi(3686)->Sigma(1385)(-)(Sigma) over bar (1385)(+))/B(J/psi ->Sigma(1385)(-)(Sigma) over bar (1385)(+)) and B(psi(3686)->Sigma(1385)(+)(Sigma) over bar (1385)(-))/B(J/psi ->Sigma(1385)(+)(Sigma) over bar (1385)(-)) are detetmind

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the form factors in the decay $D^+ \to \omega e^+ \nu_{e}$ and search for the decay $D^+ \to \phi e^+ \nu_{e}$

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

Using 2.92  fb-1 of electron-positron annihilation data collected at a center-of-mass energy of s=3.773  GeV with the BESIII detector, we present an improved measurement of the branching fraction B(D+→ωe+νe)=(1.63±0.11±0.08)×10-3. The parameters defining the corresponding hadronic form factor ratios at zero momentum transfer are determined for the first time; we measure them to be rV=1.24±0.09±0.06 and r2=1.06±0.15±0.05. The first and second uncertainties are statistical and systematic, respectively. We also search for the decay D+→ϕe+νe. An improved upper limit B(D+→ϕe+νe)<1.3×10-5 is set at 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the center-of-mass energies at BESIII via the di-muon process

Ingår i Chinese Physics C, 2016.

#### Abstract

From 2011 to 2014, the BESIII experiment collected about 5 fb$^{-1}$ data at center-of-mass energies around 4 GeV for the studies of the charmonium-like and higher excited charmonium states. By analyzing the di-muon process $e^{+}e^{-}\rightarrow\gamma_{\rm ISR/FSR}\mu^{+}\mu^{-}$, the center-of-mass energies of the data samples are measured with a precision of 0.8 MeV. The center-of-mass energy is found to be stable for most of time during the data taking.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the form factors in the decay $D^+ \to \omega e^+ \nu_{e}$ and search for the decay $D^+ \to \phi e^+ \nu_{e}$

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

Using 2.92  fb-1 of electron-positron annihilation data collected at a center-of-mass energy of s=3.773  GeV with the BESIII detector, we present an improved measurement of the branching fraction B(D+→ωe+νe)=(1.63±0.11±0.08)×10-3. The parameters defining the corresponding hadronic form factor ratios at zero momentum transfer are determined for the first time; we measure them to be rV=1.24±0.09±0.06 and r2=1.06±0.15±0.05. The first and second uncertainties are statistical and systematic, respectively. We also search for the decay D+→ϕe+νe. An improved upper limit B(D+→ϕe+νe)<1.3×10-5 is set at 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of azimuthal asymmetries in inclusive charged dipion production in $e^+e^-$ annihilations at $\sqrt{s}$ = 3.65 GeV

Ingår i PHYSICAL REVIEW LETTERS, 2016.

#### Abstract

We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process $e^+e^-\rightarrow \pi\pi X$ based on a data set of 62 $\rm{pb}^{-1}$ at the center-of-mass energy $\sqrt{s}=3.65$ GeV collected with the BESIII detector. These asymmetries can be attributed to the Collins fragmentation function. We observe a nonzero asymmetry, which increases with increasing pion momentum. As our energy scale is close to that of the existing semi-inclusive deep inelastic scattering experimental data, the measured asymmetries are important inputs for the global analysis of extracting the quark transversity distribution inside the nucleon and are valuable to explore the energy evolution of the spin-dependent fragmentation function.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for a light CP-odd Higgs boson in radiative decays of J/psi

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

We search for a light Higgs boson A(0) in the fully reconstructed decay chain of J/psi -> gamma A(0), A(0)-> mu(+)mu(-) using (225.0 +/- 2.8) x 10(6) J/psi events collected by the BESIII experiment. The A(0) is a hypothetical CP-odd light Higgs boson predicted by many extensions of the Standard Model including two spin-0 doublets plus an extra singlet. We find no evidence for A(0) production and set 90% confidence-level upper limits on the product branching fraction B(J/psi -> gamma A(0)) x B(A(0)-> mu(+)mu(-)) in the range of (2.8-495.3) x 10(-8) for 0.212 <= mA(0) <= 3.0 GeV/c(2). The new limits are five times below our previous results, and the nature of the A(0) is constrained to be mostly singlet.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for the weak decay eta ' -> K-+/-pi(-/+) and precise measurement of the branching fraction B(J/psi -> phi eta ')

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

We present the first search for the rare decay of eta' into K-+/- pi(-/+) in J/psi -> phi eta', using a sample of 1.3 x 10(9) J/psi events collected with the BESIII detector. No significant signal is observed, and the upper limit at the 90% confidence level for the ratio B(eta' -> K-+/- pi(-/+))/B(eta' -> gamma pi(+/-) pi(-/+)) is determined to be 1.3 x 10(-4). In addition, we report the measurement of the branching fraction of J/psi -> phi eta' to be [5.10 +/- 0.03(stat) +/- 0.32(syst)] x 10(-4), which agrees with previous results from BESII.

• Artikel i tidskrift

Amoroso, A.; Baldini, R.; Bertani, M.; Bettoni, D. et al.

### A cylindrical GEM detector with analog readout for the BESIII experiment

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 515-517, 2016.

#### Abstract

A cylindrical GEM detector with analog readout is under development for the upgrade of the Inner Tracker of the BESIII experiment at IHEP (Beijing). The new detector will match the requirements for momentum resolution (sigma(pt) /p(t) similar to 0.5% at 1 GeV) and radial resolution (sigma(xy) similar to 120 mu m) of the existing drift chamber and will improve significantly the spatial resolution along the beam direction (sigma(z) similar to 150 mu m) with very small material budget (less than 1.5% of X-0). With respect to the state of the art the following innovations will be deployed: a lighter mechanical structure based on Rohacell, a new XV anode readout plane with jagged strip layout to reduce the parasitic capacitance, and the use of the analogue readout inside a high intensity magnetic field to have good spatial resolution without increasing the number of channels.

• Artikel i tidskrift

Amoroso, A.; Baldini, R.; Bertani, M.; Bettoni, D. et al.

### A cylindrical GEM Inner Tracker for the BESIII experiment

Ingår i Nuovo cimento della societa italiana de fisica. C, Geophysics and space physics, 2016.

#### Abstract

We are developing a cylindrical GEM detector with analog readout to upgrade the Inner Tracker of the BESIII experiment at IHEP (Beijing). The new detector will match the requirements for momentum resolution (sigma(pt)/pt similar to 0.5% at 1GeV) and radial resolution (sigma(xy) similar to 100 mu m) of the existing drift chamber and will improve significantly the spatial resolution along the beam direction (sigma(z) similar to 150 mu m) with very small material budget (about 1% of X-0). A beam test has been performed at CERN in order to measure the performance of a BESIII GEM prototype in a magnetic field up to 1 tesla. An overview of the project and the preliminary results of the test will be presented in the talk. The project has been recognised as a Significant Research Project within the Executive Programme for Scientific and Technological Cooperation between Italy and PRC for the years 2013-2015, and more recently has been selected as one of the project funded by the European Commission within the call H2020-MSCA-RISE-2014.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Observation of an Anomalous Line Shape of the eta 'pi(+)pi(-) Mass Spectrum near the p(p)over-bar Mass Threshold in J/psi -> gamma eta 'pi(+)pi(-)

Ingår i Physical Review Letters, 2016.

#### Abstract

Using 1.09 x 10(9) J/psi events collected by the BESIII experiment in 2012, we study the J / psi -> gamma eta'pi(+)pi(-) process and observe a significant abrupt change in the slope of the eta'pi(+)pi(-) invariant mass distribution at the proton-antiproton (p (p) over bar) mass threshold. We use two models to characterize the eta'pi(+)pi(-) line shape around 1.85 GeV/c(2): one that explicitly incorporates the opening of a decay threshold in the mass spectrum (Flatte formula), and another that is the coherent sum of two resonant amplitudes. Both fits show almost equally good agreement with data, and suggest the existence of either a broad state around 1.85 GeV/c(2) with strong couplings to the c final states or a narrow state just below the p (p) over bar mass threshold. Although we cannot distinguish between the fits, either one supports the existence of a p (p) over bar moleculelike state or bound state with greater than 7 sigma significance.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of h(c) Radiative Decay h(c) -> gamma eta ' and Evidence for h(c) -> gamma eta

Ingår i Physical Review Letters, 2016.

#### Abstract

A search for radiative decays of the P-wave spin singlet charmonium resonance h(c) is performed based on 4.48 x 10(8) psi' events collected with the BESIII detector operating at the BEPCII storage ring. Events of the reaction channels h(c) -> gamma eta' and gamma eta are observed with a statistical significance of 8.4 sigma and 4.0 sigma, respectively, for the first time. The branching fractions of h(c) -> gamma eta' and h(c) -> gamma eta' are measured to be B(h(c) -> gamma eta') = (1.52 +/- 0.27 +/- 0.29) x 10(-3) and B(h(c) -> gamma eta) = (4.7 +/- 1.5 +/- 1.4) x 10(-4), respectively, where the first errors are statistical and the second are systematic uncertainties.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of pseudoscalar and tensor resonances in J/psi -> gamma phi phi

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

Based on a sample of (1310.6 +/- 10.5) x 10(6) J/psi events collected with the BESIII detector operating at the BEPCII storage ring, a partial wave analysis of the decay J/psi -> gamma phi phi is performed in order to study the intermediate states. Results of the partial wave analysis show that the structures are predominantly 0(-+) states. The existence of the eta(2225) is confirmed, and its resonance parameters are measured. Two additional pseudoscalar states, the eta(2100) with a mass of 2050(-24-26)(+30+75) MeV/c(2) and a width of 250(-30-164)(+36+181) MeV/c(2) and the X(2500) with a mass of 2470(-19-23)(+15+101) MeV/c(2) and a width of 230(-35-33)(+64+56) MeV/c(2), are observed. In addition to these three pseudoscalar states, the scalar state f(0)(2100), and three tensor states, the f(2)(2010), f(2)(2300) and f(2)(2340), are observed in the process J/psi -> gamma phi phi The product branching fractions B(J/psi -> gamma X) x B(X -> phi phi) are reported.

• Konferensbidrag

Papenbrock, Michael

### Spin observables in antihyperon-hyperon production at PANDA at FAIR

Ingår i XVI WORKSHOP ON HIGH ENERGY SPIN PHYSICS (D-SPIN2015), 2016.

#### Abstract

Hyperon production is an excellent probe of QCD in the confinement domain, and spin observables are a powerful tool in understanding the underlying physics. For the Q hyperon, seven polarisation parameters can be extracted from the angular distributions of its decay products with the future PANDA experiment at FAIR. Simulation studies reveal great prospects for strange and single charmed hyperon channels with PANDA. Software tools supporting these investigations are currently under development.

Open access
• Artikel i tidskrift

Aad, G.; Bergeås, Elin Kuutmann; Brenner, Richard; Ekelöf, Tord et al.

### Measurement of D-*+/-, D-+/- and D-S(+/-) meson production cross sections in pp collisions at root s=7 TeV with the ATLAS detector

Ingår i Nuclear Physics B, s. 717-763, 2016.

#### Abstract

The production of D*(+/-), D-+/- and D-S(+/-) charmed mesons has been measured with the ATLAS detector in pp collisions at,/7s = 7 TeV at the LHC, using data corresponding to an integrated luminosity of 280 nb(-)1(.) The charmed mesons have been reconstructed in the range of transverse momentum 3.5 < p(T)(D) < 100 GeV and pseudorapidity vertical bar eta(D)vertical bar < 2.1. The differential cross sections as a function of transverse momentum and pseudorapidity were measured for D*(+/-) and D-+/- production. The next-to-leading-order QCD predictions are consistent with the data in the visible kinematic region within the large theoretical uncertainties. Using the visible D cross sections and an extrapolation to the full kinematic phase space, the strangeness -suppression factor in charm fragmentation, the fraction of charged non -strange D mesons produced in a vector state, and the total cross section of charm production at root s = 7 TeV were derived.

Open access
• Artikel i tidskrift

Aad, G.; Bergeås, Elin Kuutmann; Brenner, Richard; Ekelöf, Tord et al.

### Search for new phenomena in final states with large jet multiplicities and missing transverse momentum with ATLAS using root s=13 TeV proton-proton collisions

Ingår i Physics Letters B, s. 334-355, 2016.

#### Abstract

Results are reported of a search for new phenomena, such as supersymmetric particle production, that could be observed in high-energy proton-proton collisions. Events with large numbers of jets, together with missing transverse momentum from unobserved particles, are selected. The data analysed were recorded by the ATLAS experiment during 2015 using the 13 TeV centre-of-mass proton-proton collisions at the Large Hadron Collider, and correspond to an integrated luminosity of 3.2 fb(-1). The search selected events with various jet multiplicities from >= 7 to >= 10 jets, and with various b-jet multiplicity requirements to enhance sensitivity. No excess above Standard Model expectations is observed. The results are interpreted within two supersymmetry models, where gluino masses up to 1400 GeV are excluded at 95% confidence level, significantly extending previous limits.

Open access
• Artikel i tidskrift

Aad, G.; Bergeås, Elin Kuutmann; Brenner, Richard; Ekelöf, Tord et al.

### Measurements of Z gamma and Z gamma gamma production in pp collisions at root s=8 TeV with the ATLAS detector

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

The production of Z bosons with one or two isolated high-energy photons is studied using pp collisions at root s = 8 TeV. The analyses use a data sample with an integrated luminosity of 20.3 fb(-1) collected by the ATLAS detector during the 2012 LHC data taking. The Z gamma and Z gamma gamma production cross sections are measured with leptonic (e(+) e(-), mu(+) mu(-), nu(nu) over bar) decays of the Z boson, in extended fiducial regions defined in terms of the lepton and photon acceptance. They are then compared to cross-section predictions from the Standard Model, where the sources of the photons are radiation off initial-state quarks and radiative Z-boson decay to charged leptons, and from fragmentation of final-state quarks and gluons into photons. The yields of events with photon transverse energy E-T > 250 GeV from l(+) l(-) gamma events and with E-T > 400 GeV from nu(nu) over bar gamma events are used to search for anomalous triple gauge-boson couplings ZZ gamma and Z gamma gamma. The yields of events with diphoton invariant mass m(gamma gamma) > 200 GeV from l(+) l(-) gamma gamma events and with m(gamma gamma) > 300 GeV from nu(nu) over bar gamma gamma events are used to search for anomalous quartic gauge-boson couplings ZZ gamma gamma and Z gamma gamma gamma. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.

Open access
• Artikel i tidskrift

Karlsson, Bengt R.

### BCCB complex Hadamard matrices of order 9, and MUBs

Ingår i Linear Algebra and its Applications, s. 309-324, 2016.

#### Abstract

A new type of complex Hadamard matrices of order 9 are constructed. The studied matrices are symmetric, block circulant with circulant blocks (BCCB) and form an until now unknown non-reducible and non-affine two-parameter orbit. Several suborbits are identified, including a one parameter intersection with the Fourier orbit F-9((4)). The defect of this new type of Hadamard matrices is observed to vary, from a generic value 2 to the anomalous values 4 and 10 for some sub-orbits, and to 12 and 16 for some single matrices. The latter matrices are shown to be related to complete sets of MUBs in dimension 9.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Measurement of the (n)over-right-arrowp -> d pi(0) pi(0) reaction with polarized beam in the region of the d(*)(2380) resonance

Ingår i European Physical Journal A, s. 1-7, 2016.

#### Abstract

We report on a high-statistics measurement of the most basic double-pionic fusion reaction over the energy region of the d (*)(2380) resonance by use of a polarized deuteron beam and observing the double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d(*) resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.

Open access
• Artikel i tidskrift

Terschlüsen, Carla; Leupold, Stefan

### Renormalisation of the low-energy constants of chiral perturbation theory from loops with dynamical vector mesons

Ingår i Physical review D, 2016.

#### Abstract

Starting from a relativistic Lagrangian for pseudoscalar Goldstone bosons and vector mesons in the antisymmetric tensor representation, a one-loop calculation is performed to pin down the divergent structures that appear for the effective low-energy action at chiral orders Q(2) and Q(4). The corresponding renormalization-scale dependencies of all low-energy constants up to chiral order Q(4) are determined. Calculations are carried out for both the pseudoscalar octet and the pseudoscalar nonet, the latter in the framework of chiral perturbation theory in the limit of a large number of colors.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C. et al.

### Measurement of Singly Cabibbo Suppressed Decays Lambda(+)(c) -> p pi(+)pi(-) and Lambda(+)(c) -> pK(+)K(-)

Ingår i Physical Review Letters, 2016.

#### Abstract

Using 567 pb(-1) of data collected with the BESIII detector at a center-of-mass energy of root s = 4.599 GeV, near the Lambda(+)(c)->(Lambda) over bar (-)(c) threshold, we study the singly Cabibbo-suppressed decays Lambda c(+) -> p pi(+) pi(-) and Lambda(+)(c) -> pK(+) K- By normalizing with respect to the Cabibbo-favored decay Lambda(+)(c)-> p pi(+)pi(-) we obtain ratios of branching fractions: [B(Lambda(+)(c) -> p pi(+)pi(-))/B(Lambda(+)(c) -> pK(-)pi(+))] = (6.70 +/- 0.48 +/- 0.25)% [B Lambda(+)(c) -> p phi)/B(Lambda(+)(c) -> pK(-)pi(+))] = (1.81 +/- 0.33 +/- 0.13)%,and [B(Lambda(+)(c) -> pK(+)K(non-phi)(-)/B(Lambda(+)(c) -> pK(-)pi(+))] (9.36 +/- 2.22 +/- 0.71)x10(-3), where the uncertainties are statistical and systematic, respectively. The absolute branching fractions are also presented. Among these measurements, the decay Lambda(+)(c) -> p pi(+)pi(-) is observed for the first time, and the precision of the branching fraction for Lambda(+)(c) -> pK(+)K(non-phi)(-) and Lambda(+)(c) -> p phi is significantly improved.

• Artikel i tidskrift

Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M. et al.

### B-s(0) lifetime measurement in the CP-odd decay channel B-s(0) -> J/Psi f(0)(980)

Ingår i PHYSICAL REVIEW D, 2016.

#### Abstract

The lifetime of the B-s(0) meson is measured in the decay channel B-s(0) -> J/Psi pi(+)pi(-) with 880 <= M pi+pi- <= 1080 MeV/c(2), which is mainly a CP-odd state and dominated by the f(0)(980) resonance. In 10.4 fb(-1) of data collected with the D0 detector in Run II of the Tevatron, the lifetime of the B-s(0) meson is measured to be tau(B-s(0)) = 1.70 +/- 0.14(stat) +/- 0.05(syst) ps. Neglecting CP violation in B-s(0)/(B) over bar (0)(s) mixing, the measurement can be translated into the width of the heavy mass eigenstate of the B-s(0), Gamma(H) = 0.59 +/- 0.05(stat) +/- 0.02(syst) ps(-1).

• Artikel i tidskrift

Abazov, V. M.; Abbott, B.; Acharya, B. S.; Adams, M. et al.

### Evidence for a B-s(0)pi(+/-) State

Ingår i Physical Review Letters, 2016.

#### Abstract

We report evidence for a narrow structure, X(5568), in the decay sequence X(5568) -> B-s(0)pi(+/-), B-s(0) -> J/psi phi, J/psi -> mu(+)mu(-), phi -> K+K-. This is evidence for the first instance of a hadronic state with valence quarks of four different flavors. The mass and natural width of this state are measured to be m = 5567.8 +/- 2.9(stat)(-1.9)(+0.9) (syst) MeV/c(2) and Gamma = 21.9 +/- 6.4(stat)(-2.5)(+5.0) (syst) MeV/c(2). If the decay is X(5568) -> B-s*pi(+/-). B-s(0)gamma pi(+/-) with an unseen gamma, m(X(5568)) will be shifted up by m(B-s*) - m(B-s(0)) similar to 49 MeV/c(2). This measurement is based on 10.4 fb(-1) of p (p) over bar collision data at root s = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.

• Artikel i tidskrift

Singh, B.; Erni, W.; Krusche, B.; Steinacher, M. et al.

### Study of doubly strange systems using stored antiprotons

Ingår i Nuclear Physics A, s. 323-340, 2016.

#### Abstract

Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the PANDA experiment at FAIR. For the first time, high resolution gamma-spectroscopy of doubly strange Lambda Lambda-hypernuclei will be performed, thus complementing measurements of ground state decays of Lambda Lambda-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Xi(-) -atoms will be feasible and even the production of Omega(-) -atoms will be within reach. The latter might open the door to the vertical bar S vertical bar = 3 world in strangeness nuclear physics, by the study of the hadronic Omega(-) -nucleus interaction. For the first time it will be possible to study the behavior of Xi(+) in nuclear systems under well controlled conditions.

• Artikel i tidskrift

Hüyük, Tayfun; Di Nitto, Antonio; Jaworski, Grzegorz; Gadea, Andrés et al.

### Conceptual design of the early implementation of the NEutron Detector Array (NEDA) with AGATA

Ingår i European Physical Journal A, 2016.

#### Abstract

The NEutron Detector Array (NEDA) project aims at the construction of a new high-efficiency compact neutron detector array to be coupled with large $\gamma$ -ray arrays such as AGATA. The application of NEDA ranges from its use as selective neutron multiplicity filter for fusion-evaporation reaction to a large solid angle neutron tagging device. In the present work, possible configurations for the NEDA coupled with the Neutron Wall for the early implementation with AGATA has been simulated, using Monte Carlo techniques, in order to evaluate their performance figures. The goal of this early NEDA implementation is to improve, with respect to previous instruments, efficiency and capability to select multiplicity for fusion-evaporation reaction channels in which 1, 2 or 3 neutrons are emitted. Each NEDA detector unit has the shape of a regular hexagonal prism with a volume of about 3.23l and it is filled with the EJ301 liquid scintillator, that presents good neutron- $\gamma$ discrimination properties. The simulations have been performed using a fusion-evaporation event generator that has been validated with a set of experimental data obtained in the 58Ni + 56Fe reaction measured with the Neutron Wall detector array.

• Artikel i tidskrift

Anastasi, A.; Babusci, D.; Bencivenni, G.; Berlowski, M. et al.

### Precision measurement of the η → π + π − π 0 Dalitz plot distribution with the KLOE detector

Ingår i Journal of High Energy Physics (JHEP), 2016.

#### Abstract

Using 1.6 fb−1 of e + e − → ϕ → ηγ data collected with the KLOE detector at DAΦNE, the Dalitz plot distribution for the η → π + π − π 0 decay is studied with the world’s largest sample of ∼ 4.7 · 106 events. The Dalitz plot density is parametrized as a polynomial expansion up to cubic terms in the normalized dimensionless variables X and Y . The experiment is sensitive to all charge conjugation conserving terms of the expansion, including a gX 2 Y term. The statistical uncertainty of all parameters is improved by a factor two with respect to earlier measurements.

Open access
• Artikel i tidskrift

Anastasi, A.; Babusci, D.; Bencivenni, G.; Berlowski, M. et al.

### Limit on the production of a new vector boson in e+e− → Uγ, U → π+π− with the KLOE experiment

Ingår i Physics Letters B, s. 356-361, 2016.

#### Abstract

Abstract The recent interest in a light gauge boson in the framework of an extra U(1) symmetry motivates searches in the mass range below 1 GeV. We present a search for such a particle, the dark photon, in e + e − → U γ , U → π + π − based on 28 million e + e − → π + π − γ events collected at DAΦNE by the KLOE experiment. The π + π − production by initial-state radiation compensates for a loss of sensitivity of previous KLOE U → e + e − , μ + μ − searches due to the small branching ratios in the ρ – ω resonance region. We found no evidence for a signal and set a limit at 90% CL on the mixing strength between the photon and the dark photon, ε 2 , in the U mass range between 527 and 987 MeV . Above 700 MeV this new limit is more stringent than previous ones.

Open access
• Artikel i tidskrift

Perotti, Elisabetta; Niblaeus, Carl; Leupold, Stefan

### Lifetime of the eta’ meson at low temperature

Ingår i Nuclear Physics A, s. 29-63, 2016.

#### Abstract

This work constitutes one part of an investigation of the low-temperature changes of the properties of the eta ' meson. In turn these properties are strongly tied to the U(1)(A) anomaly of Quantum Chromodynamics. The final aim is to explore the interplay of the chiral anomaly and in-medium effects. We determine the lifetime of an eta ' meson being at rest in a strongly interacting medium as a function of the temperature. To have a formally well-defined low-energy limit we use in a first step Chiral Perturbation Theory for a large number of colors. We determine the pertinent scattering amplitudes in leading and next-to-leading order. In a second step we include resonances that appear in the same mass range as the eta ' meson. The resonances are introduced such that the low-energy limit remains unchanged and that they saturate the corresponding low-energy constants. This requirement fixes all coupling constants. We find that the width of the eta ' meson is significantly increased from about 200 keV in vacuum to about 10 MeV at a temperature of 120 MeV.

• Artikel i tidskrift

Lalovic, N.; Louchart, C.; Michelagnoli, C.; Perez-Vidal, R. M. et al.

### Performance of the AGATA gamma-ray spectrometer in the PreSPEC set-up at GSI

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 258-266, 2016.

#### Abstract

In contemporary nuclear physics, the European Advanced GAmma Tracking Array (AGATA) represents a crucial detection system for cutting-edge nuclear structure studies. AGATA consists of highly segmented high-purity germanium crystals and uses the pulse-shape analysis technique to determine both the position and the energy of the y-ray interaction points in the crystals. It is the tracking algorithms that deploy this information and enable insight into the sequence of interactions, providing information on the full or partial absorption of the 7 ray. A series of dedicated performance measurements for an AGATA set-up comprising 21 crystals is described. This set-up was used within the recent PreSPEC-AGATA experimental campaign at the GSI Helmholtzzentrum fur Schwerionenforschung. Using the radioactive sources Co-56, Co-60 and Eu-152, absolute and normalized efficiencies and the peak-to-total of the array were measured. These quantities are discussed using different data analysis procedures. The quality of the pulse-shape analysis and the tracking algorithm are evaluated. The agreement between the experimental data and the Geant4 simulations is also investigated.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of Azimuthal Asymmetries in Inclusive Charged Dipion Production in e(+) e(-) Annihilations at root s=3.65 GeV

Ingår i Physical Review Letters, 2016.

#### Abstract

We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process e(+) e(-) -> pi pi X based on a data set of 62 pb(-1) at the center-of-mass energy of 3.65 GeV collected with the SESIII detector. These asymmetries can be attributed to the Collins fragmentation function. We observe a nonzero asymmetry, which increases with increasing pion momentum. As our energy scale is close to that of the existing semi-inclusive deep inelastic scattering experimental data, the measured asymmetries are important inputs for the global analysis of extracting the quark transversity distribution inside the nucleon and are valuable to explore the energy evolution of the spin-dependent fragmentation function.

• Artikel i tidskrift

Adolph, C.; Akhunzyanovh, R.; Alexeev, M. G.; Alexeev, G. D. et al.

### The spin structure function g(1)(p) of the proton and a test of the Bjorken sum rule

Ingår i Physics Letters B, s. 18-28, 2016.

#### Abstract

New results for the double spin asymmetry A(1)(p) and the proton longitudinal spin structure function g(1)(p) are presented. They were obtained by the COMPASS Collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH3 target. The data were collected in 2011 and complement those recorded in 2007 at 160 GeV, in particular at lower values of x. They improve the statistical precision of g(1)(p)(x) by about a factor of two in the region x less than or similar to 0.02. A next-to-leading order QCD fit to the g(1) world data is performed. It leads to a new determination of the quark spin contribution to the nucleon spin, Delta Sigma, ranging from 0.26 to 0.36, and to a re-evaluation of the first moment of g(1)(p). The uncertainty of Delta Sigma is mostly due to the large uncertainty in the present determinations of the gluon helicity distribution. A new evaluation of the Bjorken sum rule based on the COMPASS results for the non-singlet structure function g(1)(NS) (x, Q(2)) yields as ratio of the axial and vector coupling constants vertical bar gA/gV vertical bar = 1.22 +/- 0.05 (stat.) +/- 0.10 (syst.), which validates the sum rule to an accuracy of about 9%.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurements of Absolute Hadronic Branching Fractions of the Lambda(+)(c) Baryon

Ingår i Physical Review Letters, 2016.

#### Abstract

We report the first measurement of absolute hadronic branching fractions of Lambda(+)(c) baryon at the Lambda(+)(c)(Lambda) over bar (-)(c) production threshold, in the 30 years since the Lambda(+)(c) discovery. In total, 12 Cabibbo-favored Lambda(+)(c) hadronic decay modes are analyzed with a double-tag technique, based on a sample of 567 pb(-1) of e(+)e(-) collisions at root s = 4.599 GeV recorded with the BESIII detector. A global least-squares fitter is utilized to improve the measured precision. Among the measurements for twelve Lambda(+)(c) decay modes, the branching fraction for Lambda(+)(c) -> pK(-)pi(+) is determined to be (5.84 +/- 0.27 +/- 0.23)%, where the first uncertainty is statistical and the second is systematic. In addition, the measurements of the branching fractions of the other 11 Cabibbo-favored hadronic decay modes are significantly improved.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the e(+)e(-) -> pi(+) pi(-) cross section between 600 and 900 MeV using initial state radiation

Ingår i Physics Letters B, s. 629-638, 2016.

#### Abstract

We extract the e(+) e(-) -> pi(+) pi(-) cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb(-1) taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor vertical bar F pi vertical bar(2) as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (g - 2)(mu). We find this value to be a(mu)(pi pi,LO) (600-900 MeV) = (368.2 +/- 2.5(stat)+/- 3.3(sys)).10(-10), which is between the corresponding values using the BaBar or KLOE data.

Open access
• Artikel i tidskrift

Adolph, C.; Akhunzyanov, R.; Alexeev, M. G.; Alexeev, G. D. et al.

### Interplay among transversity induced asymmetries in hadron leptoproduction

Ingår i Physics Letters B, s. 406-411, 2016.

#### Abstract

In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as the Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows quantitative relationships to be established among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the branching fraction for psi(3770) -> gamma chi c0

Ingår i Physics Letters B, s. 103-109, 2016.

#### Abstract

By analyzing a data set of 2.92 fb(-1) of e(+) e(-) collision data taken at root s = 3.773 GeVand 106.41 x 10(6) psi(3686) decays taken at root s = 3.686 GeVwith the BESIII detector at the BEPCII collider, we measure the branching fraction and the partial decay width for psi(3770)->gamma chi c0 to be B(psi(3770)->gamma chi c0) = (6.88 +/- 0.28 +/- 0.67) x 10(-3) and Gamma[psi(3770)->gamma chi c0] = (187 +/- 8 +/- 19) keV, respectively. These are the most precise measurements to date.

Open access
• Artikel i tidskrift

Anastasi, Antonio; Caldeira Balkeståh, Li; Cao, Bo; Heijkenskjöld, Lena et al.

### Measurement of the ϕ→π0e+e− transition form factor with the KLOE detector

Ingår i Physics Letters B, s. 362-367, 2016.

#### Abstract

A measurement of the vector to pseudoscalar conversion decay ϕ→π0e+e− with the KLOE experiment is presented. A sample of ∼9500 signal events was selected from a data set of 1.7 fb−1 of e+e− collisions at s√∼mϕ collected at the DAΦNE e+e− collider. These events were used to obtain the first measurement of the transition form factor |Fϕπ0(q2)| and a new measurement of the branching ratio of the decay: BR(ϕ→π0e+e−)=(1.35±0.05+0.05−0.10)×10−5. The result improves significantly on previous measurements and is in agreement with theoretical predictions.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of e(+)e(-) -> omega chi(c1,2) near root s=4.42 and 4.6 GeV

Ingår i Physical Review D, 2016.

#### Abstract

Based on data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies root s > 4.4 GeV, the processes e(+)e(-) -> omega chi(c1,2) are observed for the first time. With an integrated luminosity of 1074 pb(-1) near root s = 4.42 GeV, a significant omega chi(c2) signal is found, and the cross section is measured to be (20.9 +/- 3.2 +/- 2.5) pb. With 567 pb(-1) near root s = 4.6 GeV, a clear omega chi(c2) signal is seen, and the cross section is measured to be (9.5 +/- 2.1 +/- 1.3) pb, while evidence is found for an omega chi(c2) signal. The first errors are statistical, and the second are systematic. Due to low luminosity or low cross section at other energies, no significant signals are observed. In the omega chi(c2) cross section, an enhancement is seen around root s = 4.42 GeV. Fitting the cross section with a coherent sum of the psi(4415) Breit-Wigner function and a phase-space term, the branching fraction B(psi(4415) -> omega chi(c2)) is obtained to be of the order of 10(-3).

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of the Singly Cabibbo-Suppressed Decay D+ -> omega pi(+) and Evidence for D-0 -> omega pi(0)

Ingår i Physical Review Letters, 2016.

#### Abstract

Based on 2.93 fb(-1) e(+)e(-) collision data taken at center-of-mass energy of 3.773 GeV by the BESIII detector, we report searches for the singly Cabibbo-suppressed decays D+ -> omega pi(+) and D-0 -> omega pi(0). A double tag technique is used to measure the absolute branching fractions B(D+ -> omega pi(+)) = (2.79 +/- 0.57 +/- 0.16) x 10(-4) and B(D-0 +/- omega pi(0)) = (1.17 +/- 0.34 +/- 0.07) x 10(-4), with statistical significances of 5.5 sigma and 4.1 sigma, where the first and second uncertainties are statistical and systematic, respectively.

• Artikel i tidskrift

Aad, G; Bergeaas Kuutmann, Elin; Brenner, Richard; Ekelöf, Tord et al.

### Measurement of total and differential W plus w- production cross sections in proton-proton collisions at root s=8 TeV with the ATLAS detector and limits on anomalous triple-gauge-boson couplings

Ingår i Journal of High Energy Physics (JHEP), 2016.

#### Abstract

The production of W boson pairs in proton-proton collisions at root s = 8TeV is studied using data corresponding to 20.3 fb(-1) of integrated luminosity collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The W bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with reconstructed jets are not included in the candidate event sample. A total of 6636 W W candidate events are observed. Measurements are performed in fiducial regions closely approximating the detector acceptance. The integrated measurement is corrected for all acceptance effects and for the W branching fractions to leptons in order to obtain the total W W production cross section, which is found to be 71.1 +/- 1.1( stat) + (5.7) (5.0) (syst) +/- 1 : 4( lumi) pb. This agrees with the next-to-next-to-leading-order Standard Model prediction of 63.2(+1.6) (-1.4) (scale) +/- 1.2(PDF) pb. Fiducial differential cross sections are measured as a function of each of six kinematic variables. The distribution of the transverse momentum of the leading lepton is used to set limits on anomalous triple-gauge-boson couplings.

Open access
• Konferensbidrag

Schönning, Karin

### Strong Interaction Studies with PANDA at FAIR

Ingår i 19Th International Seminar On High Energy Physics (Quarks-2016), 2016.

#### Abstract

The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, provides unique possibilities for a new generation of nuclear-, hadron-and atomic physics experiments. The future PANDA experiment at FAIR will offer a broad physics programme with emphasis on different aspects of hadron physics. Understanding the strong interaction in the perturbative regime remains one of the greatest challenges in contemporary physics and hadrons provide several important keys. In these proceedings, PANDA will be presented along with some high-lights of the planned physics programme.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Evidence for $e^+e^-\to\gamma\chi_{c1, 2}$ at center-of-mass energies from 4.009 to 4.360 GeV

Ingår i CHINESE PHYSICS C, 2015.

#### Abstract

Using data samples collected at center-of-mass energies of √s = 4.009, 4.230, 4.260, and 4.360 GeV with the BESIII detector operating at the BEPCII collider, we perform a search for the process e(+)e(−) → γχ(c)J (J=0, 1, 2) and find evidence for e(+)e(−) → γχ(c1) and e(+)e(−) → γχ(c2) with statistical significances of 3.0σ and 3.4σ, respectively. The Born cross sections σ(B)(e(+)e(−) → γχ(c)J), as well as their upper limits at the 90% confidence level (C.L.) are determined at each center-of-mass energy.

• Konferensbidrag

Xu, Goufa; Johansson, Tord; Kupsc, Andrzej; Li, Cui et al.

### Overview on BESIII results

Ingår i Nucl.Part.Phys.Proc., s. 5-9, 2015.

• Konferensbidrag

Li, Cui; Schönning, Karin; Johansson, Tord; Kupsc, Andrzej et al.

### Measurements of hadron electromagnetic structure at BESIII

Ingår i PoS EPS-HEP2015 (2015) 425, s. 425-430, 2015.

• Konferensbidrag

Garzia, Isabella; Johansson, Tord; Kupsc, Andrzej; Li, Cui et al.

### Recent results, status and prospects for the BESIII experiment

Ingår i J.Phys.Conf.Ser., 2015.

• Konferensbidrag

Pelizaeus, Marc; Johansson, Tord; Kupsc, Andrzej; Li, Cui et al.

### Recent Results from Charmonium Spectroscopy at BESIII

Ingår i Acta Phys.Polon.Supp., s. 57-64, 2015.

• Konferensbidrag

Lou, Tao; Johansson, Tord; Kupsc, Andrzej; Li, Cui et al.

### Precision Measurement of the Mass of the $\tau$ Lepton at BESIII

Ingår i Nucl.Part.Phys.Proc., s. 23-26, 2015.

• Konferensbidrag

Ripka, Martin; Schönning, Karin; Li, Cui; Johansson, Tord et al.

### Pion Form Factor Measurement at BESIII

Ingår i Acta Phys.Polon., s. 2261-2265, 2015.

• Konferensbidrag

Kuehn, Wolfgang; Johansson, Tord; Kupsc, Andrzej; Li, Cui et al.

### Recent highlights from BESIII: XYZ states

Ingår i EPJ Web Conf., s. 01008p1-01008p9, 2015.

• Artikel i tidskrift

### Partons in the chiral periphery of the nucleon

Ingår i FAIRNESS 2014: FAIR NEXT GENERATION SCIENTISTS 2014, 2015.

Open access
• Konferensbidrag

Moschner, K.; Blazhev, A.; Warr, N.; Boutachkov, P. et al.

### Study of ground and excited state decays in N approximate to Z Ag nuclei

Ingår i CGS15 - CAPTURE GAMMA-RAY SPECTROSCOPY AND RELATED TOPICS, s. 01024-, 2015.

#### Abstract

A decay spectroscopy experiment was performed within the EURICA campaign at RIKEN in 2012. It aimed at the isomer and particle spectroscopy of excited states and ground states in the mass region below the doubly magic Sn-100. The N = Z nuclei In-98, Cd-96 and Ag-94 were of particular interest for the present study. Preliminary results on the neutron deficient nuclei Ag-93 and Ag-94 are presented. In Ag-94 a more precise value for the half-life of the ground state's superallowed Fermi transition was deduced. In addition the energy spectra of the mentioned decay could be reproduced through precise Geant4 simulations of the used active stopper SIMBA. This will enable us to extract Q(beta) values from the measured data. The decay of Ag-93 is discussed based on the observed implantation-decay correlation events.

Open access
• Konferensbidrag

Lalovic, N.; Perez-Vidal, R. M.; Louchart, C.; Michelagnoli, C. et al.

### Analysis of the Response of AGATA Detectors at GSI

Ingår i CGS15 - CAPTURE GAMMA-RAY SPECTROSCOPY AND RELATED TOPICS, s. 07007-, 2015.

#### Abstract

In 2012 and 2014 the gamma-ray tracking spectrometer AGATA was operated at the SIS/FRS facility at GSI in Darmstadt, Germany. The performance of the array is discussed, outlining some important aspects of the offline data processing and analysis. Relying on the data obtained from measurements with standard gamma-ray sources, a first estimate of the photopeak efficiency and peak-to-total (P/T) is presented.

Open access
• Artikel i tidskrift

Kaminska, Daria; Caldeira Balkeståh, Li; Johansson, Tord; Kupsc, Andrzej et al.

### Study of KS semileptonic decays and CPT test with the KLOE detector

Ingår i Journal of Physics, Conference Series, 2015.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the branching fractions of D-s(+) -> eta ' X and D-s(+) -> eta 'rho(+) in e(+)e(-) -> Ds+Ds-

Ingår i Physics Letters B, s. 466-474, 2015.

#### Abstract

We study D-s(+) decays to final states involving the eta' with a 482 pb(-1) data sample collected at root s = 4.009 GeV with the BESIII detector at the BEPCII collider. We measure the branching fractions B(D-s(+) -> eta'X) = (8.8 +/- 1.8 +/- 0.5)% and B(D-s(+) > eta'rho(+)) = (5.8 +/- 1.4 +/- 0.4)% where the first uncertainty is statistical and the second is systematic. In addition, we estimate an upper limit on the non-resonant branching ratio B(D-s(+) -> eta'pi(+)pi(0)) < 5.1% at the 90% confidence level. Our results are consistent with CLEO's recent measurements and help to resolve the disagreement between the theoretical prediction and CLEO's previous measurement of B(D-s(+) -> eta'rho(+)).

Open access
• Artikel i tidskrift

Albrecht, Malte; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The Forward Endcap of the Electromagnetic Calorimeter for the PANDA Detector at FAIR

Ingår i Journal of Physics, Conference Series, 2015.

#### Abstract

The versatile 4π-detector PANDA will be built at the Facility for Antiproton and Ion Research (FAIR), an accelerator complex, currently under construction near Darmstadt, Germany. A cooled antiproton beam in a momentum range of 1.5 – 15GeV/c will be provided by the High Energy Storage Ring (HESR). All measurements at PANDA rely on an excellent performance of the detector with respect to tracking, particle identification and energy measurement. The electromagnetic calorimeter (EMC) of the PANDA detector will be equipped with 15744 PbWO(4) crystals (PWO-II), which will be operated at a temperature of – 25° C in order to increase the light output. The design of the forward endcap of the EMC has been finalized. The crystals will be read out with Large Area Avalanche Photo Diodes (LAAPDs) in the outer regions and with Vacuum Photo Tetrodes (VPTTs) in the innermost part. Production of photosensor units utilizing charge integrating preamplifiers has begun. A prototype comprised of 216 PbWO4 crystals has been built and tested at various accelerators (CERN SPS, ELSA/Bonn, MAMI/Mainz), where the crystals have been exposed to electron and photon beams of 25MeV up to 15GeV. The results of these test measurements regarding the energy and position resolution are presented.

• Artikel i tidskrift

Tiemens, Marcel; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### A Triggerless readout system for the bar PANDA electromagnetic calorimeter

Ingår i Journal of Physics, Conference Series, 2015.

#### Abstract

One of the physics goals of the future bar PANDA experiment at FAIR is to research newly discovered exotic states. Because the detector response created by these particles is very similar to the background channels, a new type of data readout had to be developed, called 'triggerless' readout. In this concept, each detector subsystem preprocesses the signal, so that in a later stage, high-level phyiscs constraints can be applied to select events of interest. A dedicated clock source using a protocol called SODANET over optical fibers ensures proper synchronisation between the components. For this new type of readout, a new way of simulating the detector response also needed to be developed, taking into account the effects of pile-up caused by the 20 MHz interaction rate.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of decay dynamics and CP asymmetry in D+ -> K(L)(0)e(+)nu(e) decay

Ingår i Physical Review D, 2015.

#### Abstract

Using 2.92 fb(-1) of electron-positron annihilation data collected at root s = 3.773 GeV with the BESIII detector, we obtain the first measurements of the absolute branching fraction B(D+ -> K(L)(0)e(+)nu(e)) = (4.481 +/- 0.027(stat) +/- 0.103(sys))% and the CP asymmetry A(CP)(D+-> KL0e+nu e) = (-0.59 +/- 0.60(stat) +/- 1.48(sys))%. From the D+ -> K(L)(0)e(+)nu(e) differential decay rate distribution, the product of the hadronic form factor and the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element, f(+)(K)(0)vertical bar V-cs vertical bar, is determined to be 0.728 +/- 0.006(stat) +/- 0.011(sys). Using vertical bar V-cs vertical bar from the SM constrained fit with the measured f(+)(K)(0)vertical bar V-cs vertical bar, f(+)(K)(0) = 0.748 +/- 0.007(stat) +/- 0.012(sys) is obtained, and utilizing the unquenched Lattice QCD (LQCD) calculation for f(+)(K)(0), vertical bar V-cs vertical bar = 0.975 +/- 0.008(stat) +/- 0.015(sys) +/- 0.025(LQCD).

Open access
• Artikel i tidskrift

Prencipe, Elisabetta; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Perspectives of open charm physics at P̄ANDA

Ingår i EPJ Web of Conferences, 2015.

#### Abstract

The $\bar PANDA$ experiment at FAIR (Facility for Antiproton and Ion Research) in Darmstadt (Germany) is designed for $\bar p p$ annihilation studies and it will investigate fundamental questions of hadron and nuclear physics in interactions of antiprotons with nucleons and nuclei. Gluonic excitations and the physics of hadrons with strange and charm quarks will be accessible with unprecedented accuracy, thereby allowing high precision tests of the strong interactions. In particular, the $D_{s0}^*(2317)^+$ and $D_{s1}(2460)^+$ are still of high interest 11 years after their discovery, because they can not be simply understood in term of potential models. The available statistics and resolution of the past experiments did not allow to clarify their nature. Recently LHCb at CERN has made progresses in this respect, but still not at the level of precision required in order to clarify the puzzle of the $cs$-spectrum. $\bar PANDA$ will be able to achieve a factor 20 higher mass resolution than attained at the B-factories, which is expected to be decisive on these and second-order open questions. The technique to evaluate the width from the excitation function of the cross section of the $D_s$ mesons will be presented, and ongoing simulations performed with $PandaRoot$ will be shown.

• Artikel i tidskrift

Kliemt, Ralf; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The PANDA experiment

Ingår i Journal of Physics, Conference Series, 2015.

#### Abstract

The PANDA (anti-Proton ANnihiliation at DArmstadt) experiment will be a multipurpose apparatus at the future Facility for Antiproton and Ion Research (FAIR) at Darmstadt. Anti-proton induced reactions with 1.5 to 15 GeV/c beam momentum at high luminosities of up to 2•10(32)/(s•cm(2)) will be investigated. Exclusive detection of whole events with almost 4π acceptance and high precision are needed for the broad physics program. The focus lies on studying the strong interaction in the charm region, by charmonium, open-charm and baryon spectroscopy, and includes the search for glueballs, hybrids and other exotics, hypernuclear physics, nucleon structure studies as well as in-medium modifications of hadrons.

• Artikel i tidskrift

Biernat, Jacek; Caldeira Balkeståhl, Li

### Feasibility studies for the Forward Spectrometer

Ingår i Journal of Physics, Conference Series, 2015.

#### Abstract

The Forward Spectrometer designed for the P̄ANDA detector will consist of many different detector systems allowing for precise track reconstruction and particle identification. Feasibility studies for Forward Spectrometer done by means of specific reactions will be presented. In the first part of the paper, results of simulations focussing on rate estimates of the tracking stations based on straw tubes will be presented. Next, the importance of the Forward Tracker will be demonstrated through the reconstruction of the ψ(4040) → DD̄ decay. Finally, results from the analysis of the experimental data collected with a straw tube prototype designed and constructed at the Research Center in Juelich will be discussed.

• Artikel i tidskrift

Tomasi-Gustafsson, Egle; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Proton electromagnetic form factors: present status and future perspectives at PANDA

Ingår i EPJ Web of Conferences, 2015.

#### Abstract

Data and models on electromagnetic proton form factors are reviewed, highlighting the contribution foreseen by the PANDA collaboration. Electromagnetic hadron form factors contain essential information on the internal structure of hadrons. Precise and surprising data have been obtained at electron accelerators, applying the polarization method in electron-proton elastic scattering. At electron-positron colliders, using initial state radiation, BABAR measured proton time-like form factors in a wide time-like kinematical region and the BESIII collaboration will measure very precisely proton and neutron form factors in the threshold region. In the next future an antiproton beam with momentum up to 15 GeV/c will be available at FAIR (Darmstadt). Measurements of the reaction p&#773; + p -> e^+ + e^- by the PANDA collaboration will contribute to the individual determination of electric and magnetic form factors in the time-like region of momentum transfer squared, as well as to their first determination in the unphysical region (below the kinematical threshold), through the reaction p&#773; + p -> e^+ + e^- + pi^0. From the discussion on feasibility studies at PANDA, we focus on the consequences of such measurements in view of an unified description of form factors in the full kinematical region. We present models which have the necessary analytical requirements and apply to the data in the whole kinematical region.

• Artikel i tidskrift

Bremer, Daniel; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Performance of prototypes for the PANDA barrel EMC

Ingår i Journal of Physics, Conference Series, 2015.

#### Abstract

The PANDA experiment will be part of the future Facility for Antiproton and Ion Research (FAIR) and aims for the study of strong interaction within the charm sector via antiproton proton collisions up to antiproton momenta of 15 GeV/c. Reflecting the variety of the physics program the PANDA detector is designed as a multi-purpose detector able to perform tracking, calorimetry and particle identification with nearly complete coverage of the solid angle. The Electromagnetic Calorimeter (EMC) contained inside its Target Spectrometer is based on cooled PbWO(4) scintillator crystals. In order to ensure an excellent performance throughout the large dynamic range of photon/electron energies ranging from a few MeV up to 15 GeV an extensive prototyping phase is mandatory. This contribution describes the measured response of the EMC barrel part prototype PROTO60 at the largest design energy to secondary beams provided by the SPS at CERN. In addition to PROTO60 a tracking station was deployed, providing precise position information of the 15 GeV/c positrons. For calibration purposes a 150 GeV/c muon beam and cosmic radiation, in combination with estimations from GEANT4 simulations were used. The obtained performance concerning energy, position and time information is presented.

• Artikel i tidskrift

Boca, Gianluigi; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The experiment PANDA: physics with antiprotons at FAIR

Ingår i EPJ Web of Conferences, 2015.

#### Abstract

PANDA is an experiment that will run at the future facility FAIR, Darmstadt, Germany. A high intensity and cooled antiproton beam will collide on a fixed hydrogen or nuclear target covering center-of-mass energies between 2.2 and 5.5 GeV. PANDA addresses various physics aspects from the low energy non-perturbative region towards the perturbative regime of QCD. With the impressive theoretical developments in this field, e.g. lattice QCD, the predictions are becoming more accurate in the course of time. The data harvest with PANDA will, therefore, be an ideal test bench with the aim to provide a deeper understanding of hadronic phenomena such as confinement and the generation of hadron masses. A variety of physics topics will be covered with PANDA, for example: the formation or production of exotic non-qqbar charm meson states connected to the recently observed XYZ spectrum; the study of gluon-rich matter, such as glueballs and hybrids; the spectroscopy of the excited states of strange and charm baryons, their production cross section and their spin correlations; the behaviour of hadrons in nuclear matter; the hypernuclear physics; the electromagnetic proton form factors in the timelike region.

• Artikel i tidskrift

Husek, Tomas; Leupold, Stefan

### Two-hadron saturation for the pseudoscalar-vector-vector correlator and phenomenological applications

Ingår i European Physical Journal C, 2015.

#### Abstract

The pseudoscalar-vector-vector correlator is constructed using two mesonmultiplets in the vector and two in the pseudoscalar channel. The parameters are constrained by the operator product expansion at leading order where two or all three momenta are considered as large. Demanding in addition the Brodsky-Lepage limit one obtains (in the chiral limit) a pion-vector-vector (pi VV) correlator with only one free parameter. The singly virtual pion transition form factor F-pi 0 gamma gamma* and the decay width of omega -> pi(0)gamma. are independent of this parameter and can serve as cross-checks of the results. The free parameter is determined from a fit of the omega-pi transition form factor F-pi 0 omega gamma*. The resulting pi VV correlator is used to calculate the decay widths omega -> pi(0) e(+) e(-) and omega -> pi(0) mu(+) mu(-) and finally the widths of the rare decay pi(0) -> e(+) e(-) and of the Dalitz decay pi(0) -> e(+) e(-) gamma(.) Incorporating radiative QED corrections the calculations of pi(0) decays are compared to the KTeV results. We find a deviation of 2 sigma or less for the rare pion decay.

Open access
• Artikel i tidskrift

Anastasi, A.; Babusci, D.; Bencivenni, G.; Berlowski, M. et al.

### Limit on the production of a low-mass vector boson in e(+)e(-) -> U gamma, U -> e(+)e(-) with the KLOE experiment

Ingår i Physics Letters B, s. 633-637, 2015.

#### Abstract

The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the U boson, with the KLOE detector at the DA Phi NE e(+)e(-) collider. Using an integrated luminosity of 1.54 fb(-1), we studied the process e(+)e(-) -> U gamma, with U -> e(+)e(-), using radiative return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90% CL upper limit on the mixing strength between the Standard Model photon and the dark photon, epsilon(2), at 10(-6)-10(-4) in the 5-520 MeV/c(2) mass range.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of a Neutral Structure near the D(D)over-bar* Mass Threshold in e(+)e(-) -> (D(D)over-bar*)(0)pi(0) at root s=4.226 and 4.257 GeV

Ingår i Physical Review Letters, 2015.

#### Abstract

A neutral structure in the D (D) over bar* system around the D (D) over bar* mass threshold is observed with a statistical significance greater than 10 sigma in the processes e(+)e(-) -> D+D*(-)pi(0) + c.c. and e(+)e(-) -> D-0(D) over bar*(0)pi(0) + c.c. at root s = 4.226 and 4.257 GeV in the BESIII experiment. The structure is denoted as Z(c)(3885)(0). Assuming the presence of a resonance, its pole mass and width are determined to be [3885.7(-5.7)(+4.3) (stat) +/- 8.4(syst)] MeV/c(2) and [35(-12)(+11) (stat) +/- 15(syst)] MeV, respectively. The Born cross sections are measured to be sigma[e(+)e(-) -> Z(c)(3885)(0)pi(0); Z(c)(3885)(0) -> D (D) over bar*] = [77 +/- 13(stat) +/- 17(syst)] pb at 4.226 GeV and [47 +/- 9(stat) +/- 10(syst)] pb at 4.257 GeV. The ratio of decay rates B[Z(c)(3885)(0) -> D+D*(-) + c.c.]/B[Z(c)(3885)(0) -> D-0(D) over bar*(0) + c.c.] is determined to be 0.96 +/- 0.18(stat) +/- 0.12(syst), consistent with no isospin violation in the process, Z(c)(3885)(0) -> D (D) over bar*.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the Absolute Branching Fraction for Lambda(+)(c) -> Lambda e(+)nu(e)

Ingår i Physical Review Letters, 2015.

#### Abstract

We report the first measurement of the absolute branching fraction for Lambda(+)(c) -> Lambda e(+)nu(e). This measurement is based on 567 pb(-1) of e(+)e(-) annihilation data produced at root s = 4.599 GeV, which is just above the Lambda(+)(c)Lambda(-)(c) threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be B(Lambda(+)(c) -> Lambda e(+)nu(e)) = [3.63 +/- 0.38(stat) +/- 0.20(syst)] %, representing a significant improvement in precision over the current indirect determination. As the branching fraction for Lambda(+)(c) -> Lambda e(+)nu(e) is the benchmark for those of other Lambda(+)(c) semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### An improved limit for Gamma(ee) of X(3872) and Gamma(ee) measurement of psi(3686)

Ingår i Physics Letters B, s. 414-420, 2015.

#### Abstract

Using the data sets taken at center-of-mass energies above 4 GeV by the BESIII detector at the BEPCII storage ring, we search for the reaction e(+)e(-) -> gamma(ISR) X(3872) -> gamma(ISR)pi(+)pi(-) J/psi via the Initial State Radiation technique. The production of a resonance with quantum numbers J(PC) = 1(++) such as the X(3872) via single photon e(+)e(-) annihilation is forbidden, but is allowed by a next-to-leading order box diagram. We do not observe a significant signal of X(3872), and therefore give an upper limit for the electronic width times the branching fraction Gamma B-X(3872)(ee)(X(3872) -> pi(+)pi(-) J/psi) < 0.13 eVat the 90% confidence level. This measurement improves upon existing limits by a factor of 46. Using the same final state, we also measure the electronic width of the psi(3686) to be Gamma(psi)(ee)(3686) ee = 2213 +/- 18(stat) +/- 99(sys) eV.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of Z(c)(3900)(0) in e(+)e(-) -> pi(0)pi(0) J/Psi

Ingår i Physical Review Letters, 2015.

#### Abstract

Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, we observe a new neutral state Z(c)(3900)(0) with a significance of 10.4 sigma. The mass and width are measured to be 3894.8 +/- 2.3 +/- 3.2 MeV/c(2) and 29.6 +/- 8.2 +/- 8.2 MeV, respectively, where the first error is statistical and the second systematic. The Born cross section for e(+)e(-) -> pi(0)pi(0) J/Psi and the fraction of it attributable to pi(0)Z(c)(3900)(0) -> pi(0)pi(0) J/Psi in the range E-c.m. = 4.19-4.42 GeV are also determined. We interpret this state as the neutral partner of the four-quark candidate Z(c)(3900)(+/-).

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for Z(c)(3900)(+/-) -> omega pi(+/-)

Ingår i Physical Review D, 2015.

#### Abstract

The decay Z(c)(3900)(+/-) -> omega pi(+/-) is searched for using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies root s = 4.23 and 4.26 GeV. No significant signal for the Z(c)(3900)(+/-) is found, and upper limits at the 90% confidence level on the Born cross section for the process e(+)e(-) -> Z(c)(3900)(+/-) pi(-/+) -> omega pi(+)pi(-) are determined to be 0.26 and 0.18 pb at root s = 4.23 and 4.26 GeV, respectively.

• Artikel i tidskrift

Vogt, A.; Birkenbach, B.; Reiter, P.; Corradi, L. et al.

### Light and heavy transfer products in Xe-136+U-238 multinucleon transfer reactions

Ingår i Physical Review C. Nuclear Physics, 2015.

#### Abstract

Background: Multinucleon transfer reactions (MNT) are a competitive tool to populate exotic neutron-rich nuclei in a wide region of nuclei, where other production methods have severe limitations or cannot be used at all. Purpose: Experimental information on the yields of MNT reactions in comparison with theoretical calculations are necessary to make predictions for the production of neutron-rich heavy nuclei. It is crucial to determine the fraction of MNT reaction products which are surviving neutron emission or fission at the high excitation energy after the nucleon exchange. Method: Multinucleon transfer reactions in Xe-136 + U-238 have been measured in a high-resolution gamma-ray/particle coincidence experiment. The large solid-angle magnetic spectrometer PRISMA coupled to the high-resolution Advanced Gamma Tracking Array (AGATA) has been employed. Beamlike reaction products after multinucleon transfer in the Xe region were identified and selected with the PRISMA spectrometer. Coincident particles were tagged by multichannel plate detectors placed at the grazing angle of the targetlike recoils inside the scattering chamber. Results: Mass yields have been extracted and compared with calculations based on the GRAZING model for MNT reactions. Kinematic coincidences between the binary reaction products, i.e., beamlike and targetlike nuclei, were exploited to obtain population yields for nuclei in the actinide region and compared to x-ray yields measured by AGATA. Conclusions: No sizable yield of actinide nuclei beyond Z = 93 is found to perform nuclear structure investigations. In-beam gamma-ray spectroscopy is feasible for few-neutron transfer channels in U and the -2p channel populating Th isotopes.

• Artikel i tidskrift

### Quantum-mechanical picture of peripheral chiral dynamics

Ingår i Physical Review C. Nuclear Physics, 2015.

#### Abstract

The nucleon's peripheral transverse charge and magnetization densities are computed in chiral effective field theory. The densities are represented in first-quantized form, as overlap integrals of chiral light-front wave functions describing the transition of the nucleon to soft pion-nucleon intermediate states. The orbital motion of the pion causes a large left-right asymmetry in a transversely polarized nucleon. The effect attests to the relativistic nature of chiral dynamics [pion momenta k = O(M-pi)] and could be observed in form factor measurements at low momentum transfer.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation and Spin-Parity Determination of the X(1835) in J/psi -> gamma(KSKS0)-K-0 eta

Ingår i Physical Review Letters, 2015.

#### Abstract

We report an observation of the process J/psi -> gamma X(1835) -> gamma(KSKS0)-K-0 eta at low (KSKS0)-K-0 mass with a statistical significance larger than 12.9s using a data sample of 1.31 x 109 J/psi events collected with the BESIII detector. In this region of phase space the (KSKS0)-K-0 system is dominantly produced through the f (0)(980). By performing a partial wave analysis, we determine the spin parity of the Xd1835_ to be J(PC) = 0(-+). The mass and width of the observed X(1835) are 1844 +/- 9(stat)(-25)(+16)(syst) MeV/c(2) and 192(-17)(+20)(sta)(-43)(+62)(syst) MeV, respectively, which are consistent with the results obtained by BESIII in the channel J/psi -> gamma pi(+)pi(-)eta'.

• Artikel i tidskrift

Singh, B. P.; Erni, W.; Keshelashvili, I.; Krusche, B. et al.

### Experimental access to Transition Distribution Amplitudes with the PANDA experiment at FAIR

Ingår i European Physical Journal A, 2015.

#### Abstract

Baryon-to-meson Transition Distribution Amplitudes (TDAs) encoding valuable new information on hadron structure appear as building blocks in the collinear factorized description for several types of hard exclusive reactions. In this paper, we address the possibility of accessing nucleon-to-pion (pi N) TDAs from (p) over barp -> e(+)e(-)pi(0) reaction with the future PANDA detector at the FAIR facility. At high center-of-mass energy and high invariant mass squared of the lepton pair q(2), the amplitude of the signal channel (p) over barp -> e(+)e(-)pi(0) admits a QCD factorized description in terms of pi N TDAs and nucleon Distribution Amplitudes (DAs) in the forward aid backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring (p) over barp -> e(+)e(-)pi(0) with the PANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e. (p) over barp -> pi(+)pi(-)pi(0) were performed for the center-of-mass energy squared s = 5 GeV2 and s = 10 GeV2, in the kinematic regions 3.0 < q(2) < 4.3 GeV2 and 5 < q(2) < 9 GeV2, respectively, with a neutral pion scattered in the forward or backward cone vertical bar cos theta(pi 0)vertical bar > 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the PANDA detector will allow to achieve a background rejection factor of 5 . 10(7) (1 . 10(7)) at low (high) q(2) for s = 5 GeV2, and of 1 . 10(8) (6 . 10(6)) at low (high) q(2) for s = 10 GeV2, while keeping the signal reconstruction efficiency at around 40%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 of integrated luminosity. The cross sections obtained from the simulations are used to show that a test of QCD collinear factorization can be done at the lowest order by measuring scaling laws and angular distributions. The future measurement of the signal channel cross section with PANDA will provide a new test of the perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing pi N TDAs.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Amplitude analysis of the pi(0)pi(0) system produced in radiative J/psi decays

Ingår i Physical Review D, 2015.

#### Abstract

An amplitude analysis of the pi(0)pi(0) system produced in radiative J/psi decays is presented. In particular, a piecewise function that describes the dynamics of the pi(0)pi(0) system is determined as a function of M pi(0)pi(0) from an analysis of the (1.311 +/- 0.011) x 10(9) J/psi decays collected by the BESIII detector. The goal of this analysis is to provide a description of the scalar and tensor components of the pi(0)pi(0) system while making minimal assumptions about the properties or number of poles in the amplitude. Such a model-independent description allows one to integrate these results with other related results from complementary reactions in the development of phenomenological models, which can then be used to directly fit experimental data to obtain parameters of interest. The branching fraction of J/psi -> pi(0)pi(0) is determined to be (1.15 +/- 0.05) x 10(-3), where the uncertainty is systematic only and the statistical uncertainty is negligible.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of eta ' -> omega e(+)e(-)

Ingår i Physical Review D, 2015.

#### Abstract

Based on a sample of eta' mesons produced in the radiative decay J/psi -> gamma eta' in 1.31 x 10(9) J/psi events collected with the BESIII detector, the decay eta' -> omega e(+)e(-) is observed for the first time, with a statistical significance of 8 sigma. The branching fraction is measured to be B(eta' -> omega e(+)e(-)) = (1.97 +/- 0.34(stat) +/- 0.17(syst)) x 10(-4), which is in agreement with theoretical predictions. The branching fraction of eta' -> omega gamma is also measured to be (2.55 +/- 0.03(stat) +/- 0.16(syst)) x 10(-2), which is the most precise measurement to date, and the relative branching fraction B(eta' -> omega e(+)e(-))/B(eta' -> omega gamma) is determined to be (7.71 +/- 1.34(stat) +/- 0.54(syst)) x 10(-3).

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of a Neutral Charmoniumlike State Z(c)(4025)(0) in e(+)e(-) -> (D*(D)over-bar*)(0)pi(0)

Ingår i Physical Review Letters, 2015.

#### Abstract

We report a study of the process e(+)e(-) -> (D*(D) over bar*)(0)pi(0) using e(+)e(-) collision data samples with integrated luminosities of 1092 pb(-1) at root s = 4.23 GeV and 826 pb(-1) at root s = 4.26 GeV collected with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the (D*(D) over bar*)(0) mass threshold in the pi(0) recoil mass spectrum, which we denote as Z(c)(4025)(0). Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be (4025.5(-4.7)(+2.0) +/- 3.1) MeV/c(2) and (23.0 +/- 6.0 +/- 1.0) MeV, respectively. The Born cross sections of e(+)e(-) -> Z(c)(4025)(0)pi(0) -> (D*(D) over bar*)(0)pi(0) are measured to be (61.6 +/- 8.2 +/- 9.0) pb at root s = 4.23 GeV and (43.4 +/- 8.0 +/- 5.4) pb at root s = 4.26 GeV. The first uncertainties are statistical and the second are systematic.

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Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of dynamics of D-0 -> K(-)e(+)nu(e) and D-0 -> pi(-)e(+)nu(e) decays

Ingår i Physical Review D, 2015.

#### Abstract

In an analysis of a 2.92 fb(-1) data sample taken at 3.773 GeV with the BESIII detector operated at the BEPCII collider, we measure the absolute decay branching fractions B(D-0 -> K(-)e(+)nu(e)) = (3.505 +/- 0.014 +/- 0.033)% and B(D-0 -> pi(-)e(+)nu(e)) = (0.295 +/- 0.004 +/- 0.003)%. From a study of the differential decay rates we obtain the products of hadronic form factor and the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element f(+)(K)(0)vertical bar V-cs vertical bar = 0.7172 +/- 0.0025 +/- 0.0035 and f(+)(pi)(0)vertical bar V-cd vertical bar = 0.1435 +/- 0.0018 +/- 0.0009. Combining these products with the values of vertical bar V-cs(d)vertical bar from the SM constraint fit, we extract the hadronic form factors f(+)(K)(0) = 0.7368 +/- 0.0026 +/- 0.0036 and f(+)(pi)(0) = 0.6372 +/- 0.0080 +/- 0.0044, and their ratio f(+)(pi)(0)/f(+)(K)(0) = 0.8649 +/- 0.0112 +/- 0.0073. These form factors and their ratio are used to test unquenched lattice QCD calculations of the form factors and a light cone sum rule (LCSR) calculation of their ratio. The measured value of f(+)(K(pi))(0)vertical bar V-cs(d)vertical bar and the lattice QCD value for f(+)(K(pi))(0) are used to extract values of the CKM matrix elements of vertical bar V-cs vertical bar = 0.9601 +/- 0.0033 +/- 0.0047 +/- 0.0239 and vertical bar V-cd vertical bar = 0.2155 +/- 0.0027 +/- 0.0014 +/- 0.0094, where the third errors are due to the uncertainties in lattice QCD calculations of the form factors. Using the LCSR value for f(+)(pi)(0)/f(+)(K)(0), we determine the ratio vertical bar V-cd vertical bar/vertical bar V-cs vertical bar = 0.238 +/- 0.004 +/- 0.002 +/- 0.011, where the third error is from the uncertainty in the LCSR normalization. In addition, we measure form factor parameters for three different theoretical models that describe the weak hadronic charged currents for these two semileptonic decays. All of these measurements are the most precise to date.

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Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the form factors in the decay D+ -> omega e(+)nu(e) and search for the decay D+ -> phi e(+)nu(e)

Ingår i Physical Review D, 2015.

#### Abstract

Using 2.92 fb(-1) of electron-positron annihilation data collected at a center-of-mass energy of root s = 3.773 GeV with the BESIII detector, we present an improved measurement of the branching fraction B(D+ -> omega e(+)nu(e)) = (1.63 +/- 0.11 +/- 0.08) x 10(-3). The parameters defining the corresponding hadronic form factor ratios at zero momentum transfer are determined for the first time; we measure them to be r(V) = 1.24 +/- 0.09 +/- 0.06 and r(2) = 1.06 +/- 0.15 +/- 0.05. The first and second uncertainties are statistical and systematic, respectively. We also search for the decay D+ -> phi e(+)nu(e). An improved upper limit B(D+ -> phi e(+)nu(e)) < 1.3 x 10(-5) is set at 90% confidence level.

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Birkenbach, B.; Vogt, A.; Geibel, K.; Recchia, F. et al.

### Spectroscopy of the neutron-rich actinide nucleus U-240 following multinucleon-transfer reactions

Ingår i Physical Review C. Nuclear Physics, 2015.

#### Abstract

Background: Nuclear structure information for the neutron-rich actinide nuclei is important since it is the benchmark for theoretical models that provide predictions for the heaviest nuclei. Purpose: gamma-ray spectroscopy of neutron-rich heavy nuclei in the actinide region. Method: Multinucleon-transfer reactions in Zn-70 + U-238 and Xe-136 + U-238 have been measured in two experiments performed at the INFN Legnaro, Italy. In the Zn-70 experiment the high-resolution HPGe Clover Array (CLARA) coupled to the magnetic spectrometer PRISMA was employed. In the Xe-136 experiment the high-resolution Advanced Gamma Tracking Array (AGATA) was used in combination with PRISMA and the Detector Array for Multinucleon Transfer Ejectiles (DANTE). Results: The ground-state band (g.s. band) of U-240 was measured up to the 20(+) level and a tentative assignment was made up to the (24(+)) level. Results from gamma gamma coincidence and from particle coincidence analyses are shown. Moments of inertia (MoI) show a clear upbend. Evidence for an extended first negative-parity band of U-240 is found. Conclusions: A detailed comparison with latest calculations shows best agreement with cranked relativistic Hartree-Bogoliubov (CRHB) calculations for the g.s. band properties. The negative-parity band shows the characteristics of a K-pi = 0 band based on an octupole vibration.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Precision measurement of the integrated luminosity of the data taken by BESIII at center-of-mass energies between 3.810 GeV and 4.600 GeV

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2015.

#### Abstract

From December 2011 to May 2014, about 5 fb(-1) of data were taken with the BESIII detector at center-ofmass energies between 3.810 GeV and 4.600 GeV to study the charmonium-like states and higher excited charmonium states. The time-integrated luminosity of the collected data sample is measured to a precision of 1% by analyzing events produced by the large-angle Bhabha scattering process.

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• Artikel i tidskrift

Ruchowska, E.; Mach, H.; Kowal, M.; Skalski, J. et al.

### Search for octupole correlations in Nd-147

Ingår i Physical Review C. Nuclear Physics, 2015.

#### Abstract

Properties of excited states in Nd-147 have been studied with the multispectra and gamma gamma coincidencemeasurements. Twenty-four new gamma lines and three new levels have been introduced into the level scheme of Nd-147. Using the advanced time-delayed beta gamma gamma(t) method, we measured lifetimes of eight excited levels in Nd-147, populated via the beta decay of Pr-147. We have determined reduced transition probabilities for 30 gamma transitions. Multidimensional potential energy surface calculations performed for Nd-147 suggest two single-quasiparticle configurations with nonzero octupole deformation, with K = 1/2 and K = 5/2. Our calculations also predict a sizable value of the electric dipole moment vertical bar D-0 vertical bar = 0.26e fm for this nucleus, while experimentally, a lower limit of vertical bar D-0 vertical bar >= 0.02e fm has been evaluated for the supposed K = 1/2 parity doublet. In contrast to the theoretical results, we do not observe the parity doublet bands with K = 5/2. This, and the lack of theoretically expected E1 strength in Nd-147,Nd-149 may signal some poorly understood structural effect in the odd-N lanthanides.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Confirmation of a charged charmoniumlike state Z(c)(3885)(-/+) in e(+)e(-) -> pi(+/-) (D(D)over-bar*)(-/+) with double D tag

Ingår i Physical Review D, 2015.

#### Abstract

We present a study of the process e(+)e(-) -> pi(+/-) (D (D) over bar*)(-/+) using data samples of 1092 pb(-1) at root s = 4.23 GeV and 826 pb(-1) at root s = 4.26 GeV collected with the BESIII detector at the BEPCII storage ring. With full reconstruction of the D meson pair and the bachelor pi(+) in the final state, we confirm the existence of the charged structure Z(c) (3885)(-/+) in the (D (D) over bar*)(-/+) system in the two isospin processes e(+)e(-) -> pi(+DD)-D-0*(-) and e(+)e(-) -> pi+D-D*(0). By performing a simultaneous fit, the statistical significance of Zc(3885)(-/+) signal is determined to be greater than 10 sigma, and its pole mass and width are measured to be M-pole = (3881.7 +/- 1.6(stat) +/- 1.6(syst)) MeV/c(2) and Gamma(pole) = (26.6 +/- 2.0(stat) +/- 2.1(syst)) MeV, respectively. The Born cross section times the (D (D) over bar*)(-/+) branching fraction (sigma(e(+)e(-) -> pi(+/-)Z(c)(3885)(-/+)) x Br(Z(c)(3885)(-/+) -> (D (D) over bar*)(-/+) )) is measured to be (141.6 +/- 7.9(stat) +/- 12.3(syst)) pb at root s = 4.23 GeV and (108.4 +/- 6.9(stat) +/- 8.8(syst)) pb at root s = 4.26 GeV. The polar angular distribution of the pi(+) - Z(c)(3885)(-/+) system is consistent with the expectation of a quantum number assignment of J(P) = 1(+) for Z(c)(3885)(-/+).

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the matrix elements for the decays eta -> pi(+)pi(-)pi(0) and eta/eta ' -> pi(0)pi(0)pi(0)

Ingår i Physical Review D, 2015.

#### Abstract

Based on a sample of 1.31 x 10(9) J/psi events collected with the BESIII detector at the BEPCII collider, Dalitz plot analyses of selected 79,625 eta -> pi(+)pi(-)pi(0) events, 33,908 eta -> pi(0)pi(0)pi(0) events, and 1,888 eta' -> pi(0)pi(0)pi(0) events are performed. The measured matrix elements of eta -> pi(+)pi(-)pi(0) are in reasonable agreement with previous measurements. The Dalitz plot slope parameters of eta -> pi(0)pi(0)pi(0) and eta' -> pi(0)pi(0)pi(0) are determined to be -0.055 +/- 0.014 +/- 0.004 and -0.640 +/- 0.046 +/- 0.047, respectively, where the first uncertainties are statistical and the second systematic. Both values are consistent with previous measurements, while the precision of the latter one is improved by a factor of 3. Final state interactions are found to have an important role in those decays.

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### Light-front representation of chiral dynamics in peripheral transverse densities

Ingår i Journal of High Energy Physics (JHEP), 2015.

#### Abstract

The nucleon's electromagnetic form factors are expressed in terms of the transverse densities of charge and magnetization at fixed light-front time. At peripheral transverse distances b - O(M-pi(-1)) the densities are governed by chiral dynamics anti can be calculated model-independently using chiral effective field theory (EFT). We represent the leading-order chiral EFT results for the peripheral transverse densities as overlap integrals of chiral light-front wave functions, describing the transition of the initial nucleon to soft pion-nucleon intermediate states and back. The new representation (a) explains the parametric order of the peripheral transverse densities; (b) establishes an inequality between the spin-independent and -dependent densities; (c) exposes the role of pion orbital angular momentum in chiral dynamics; (d) reveals a large left-right asymmetry of the current in a transversely polarized nucleon and suggests a simple interpretation. The light-front representation enables a first-quantized, quantum-mechanical view of chiral dynamics that is fully relativistic and exactly equivalent to the second-quantized, field-theoretical formulation. It relates the charge and magnetization densities measured in low-energy elastic scattering to the generalized parton distributions probed in peripheral high-energy scattering processes. The method can be applied to nucleon form factors of other operators, e.g. the energy-momentum tensor.

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Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of the isospin-violating decay J/psi -> phi pi(0)f(0) (980)

Ingår i Physical Review D, 2015.

#### Abstract

Using a sample of 1.31 x 10(9) J/psi events collected with the BESIII detector at the BEPCII collider, the decays J/psi -> phi pi(+)pi(-)pi(0) and J/psi -> phi pi(0)pi(0)pi(0) are investigated. The isospin- violating decay J/psi -> phi pi(0)f(0)(980) with f(0)(980)-> pi pi is observed for the first time. The width of the f(0)(980) obtained from the dipion mass spectrum is found to be much smaller than the world average value. In the pi(0)f(0)(980) mass spectrum, there is evidence of f(1)(1285) production. By studying the decay J/psi ->eta', the branching fractions of eta' -> pi(+)pi(-)pi(0) and eta' -> pi(0)pi(0)pi(0), as well as their ratio, are also measured.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for the isospin violating decay Y(4260)-> J/psi eta pi(0)

Ingår i Physical Review D, 2015.

#### Abstract

Using data samples collected at center-of-mass energies of root s = 4.009, 4.226, 4.257, 4.358, 4.416, and 4.599 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the isospin violating decay Y(4260)-> J/psi eta pi(0). No signal is observed, and upper limits on the cross section sigma(e(+)e(-) -> J/psi eta pi(0)) at the 90% confidence level are determined to be 3.6, 1.7, 2.4, 1.4, 0.9, and 1.9 pb, respectively.

• Artikel i tidskrift

Anastasi, A.; Babusci, D.; Bencivenni, G.; Berlowski, M. et al.

### Search for dark Higgsstrahlung in e(+0)e(-) -> mu(+)mu(-) and missing energy events with the KLOE experiment

Ingår i Physics Letters B, s. 365-372, 2015.

#### Abstract

We searched for evidence of a Higgsstrahlung process in a secluded sector, leading to a final state with a dark photon U and a dark Higgs boson h', with the KLOE detector at DA Phi NE. We investigated the case of h' lighter than U, with U decaying into a muon pair and h' producing a missing energy signature. We found no evidence of the process and set upper limits to its parameters in the range 2m(mu) < m(U) < 1000 MeV, m(h') < m(U). (C) 2015 The Authors. Published by Elsevier B.V.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of J/psi -> eta phi pi(+)pi(-) at BESIII

Ingår i Physical Review D, 2015.

#### Abstract

invariant mass spectrum of phi f(0)(980) with a statistical significance of greater than 10 sigma. The corresponding mass and width are determined to be M = 2200 +/- 6(stat) +/- 5(syst) MeV/c(2) and Gamma = 104 +/- 15(stat) +/- 15(syst) MeV, respectively, and the product branching fraction is measured to be B(J/psi ->eta Y(2175), Y(2175)->phi f(0)(980), f(0)(980)->pi(+)pi(-)) = (1.20 +/- 0.14(stat)+/- 0.37(syst))x10(-4). The results are consistent within errors with those of previous experiments. We also measure the branching fraction of J/psi ->phi f(1)(1285) with f(1)(1285)->eta pi(+)pi(-) and set upper limits on the branching fractions for J/psi ->phi eta(1405)/phi X(1835)/phi X(1870) with eta(1405)/X(1835)/X(1870)->eta pi(+)pi(-) at the 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for the Y(4140) via e(+)e(-) -> gamma phi J/psi at root s=4.23, 4.26 and 4.36 GeV

Ingår i Physical Review D, 2015.

#### Abstract

Using data samples collected at center-of-mass energies root s = 4.23, 4.26, and 4.36 GeV with the BESIII detector operating at the BEPCII storage ring, we search for the production of the charmoniumlike state Y(4140) through a radiative transition followed by its decay to phi J/psi. No significant signal is observed and upper limits on sigma[e(+)e(-) -> gamma Y(4140)] . B(Y(4140) -> phi J/psi at the 90% confidence level are estimated as 0.35, 0.28, and 0.33 pb at root s = 4.23, 4.26, and 4.36 GeV, respectively.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of e(+)e(-) -> omega chi(cJ) at Center of Mass Energies from 4.21 to 4.42 GeV

Ingår i Physical Review Letters, 2015.

#### Abstract

Based on data samples collected with the BESIII detector at the BEPCII collider at nine center of mass energies from 4.21 to 4.42 GeV, we search for the production of e(+)e(-) -> omega chi(cJ) (J = 0, 1, 2). The process e(+)e(-) -> omega chi(c0) is observed for the first time, and the Born cross sections at root s = 4.23 and 4.26 GeV are measured to be (55.4 +/- 6.0 +/- 5.9) and (23.7 +/- 5.3 +/- 3.5) pb, respectively, where the first uncertainties are statistical and the second are systematic. The omega chi(c0) signals at the other seven energies and the e(+)e(-) -> omega chi(c1) and omega chi(c2) signals are not significant, and the upper limits on the cross sections are determined. By examining the omega chi(c0) cross section as a function of center of mass energy, we find that it is inconsistent with the line shape of the Y(4260) observed in e(+)e(-) -> pi(+)pi(-) J/psi Assuming the omega chi(c0) signals come from a single resonance, we extract the mass and width of the resonance to be (4230 +/- 8 +/- 6) MeV/c(2) and (38 +/- 12 +/- 2) MeV, respectively, and the statistical significance is more than 9 sigma.

• Artikel i tidskrift

Fäldt, Göran

### Entanglement in joint Lambda(Lambda)over-bar decay

Ingår i European Physical Journal A, 2015.

#### Abstract

We investigate the joint decay in the reaction . This reaction may provide information on the electromagnetic form factors of the Lambda baryon, in the time-like region. We present a conventional diagram-based calculation where production and decay steps are coherent and summations over final-state proton and anti-proton spins are performed. The resulting cross-section distribution is explicitly covariant as it is expressed in scalar products of the four-momentum vectors of the participating particles. We compare this calculation with that of the folding method which we extend and make explicitly covariant. In the folding method production and decay distributions, not amplitudes, are folded together. Of particular importance is then a correct counting of the number of possible intermediate-hyperon-spin states.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for D-0 -> gamma gamma and improved measurement of the branching fraction for D-0 -> pi(0)pi(0)

Ingår i Physical Review D, 2015.

#### Abstract

Using 2.92 fb(-1) of electron-positron annihilation data collected at root s = 3.773 GeV with the BESIII detector, we report the results of a search for the flavor-changing neutral current process D-0 -> gamma gamma using a double-tag technique. We find no signal and set an upper limit at 90% confidence level for the branching fraction of B(D-0 -> gamma gamma < 3.8 x 10(-6). We also investigate D-0-meson decay into two neutral pions, obtaining a branching fraction of B(D-0 -> pi(0)pi(0)) = (8.24 +/- 0.21(stat) +/- 0.30(syst)) x 10(-4), the most precise measurement to date and consistent with the current world average.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Searches for isospin-violating transitions chi(c0,2) -> pi(0)eta(c)

Ingår i Physical Review D, 2015.

#### Abstract

We present the first upper-limit measurement of the branching fractions of the isospin-violating transitions chi(c0,2) -> pi(0)eta(c). The measurements are performed using 106 x 10(6) psi(3686) events accumulated with the BESIII detector at the BEPCII e(+)e(-) collider at a center-of-mass energy corresponding to the psi(3686) mass. We obtained upper limits on the branching fractions at a 90% confidence level of B(chi(c0) -> pi(0)eta(c)) < 1.6 x 10(-3) and B(chi(c2) -> pi(0)eta(c)) < 3.2 x 10(-3).

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of y(CP) in D-0-(D)over-bar(0) oscillation using quantum correlations in e(+)e(-) -> D-0(D)over-bar(0) at root s=3.773 GeV

Ingår i Physics Letters B, s. 339-346, 2015.

#### Abstract

We report a measurement of the parameter y(CP) in D-0-(D) over bar (0) oscillations performed by taking advantage of quantum coherence between pairs of D-0(D) over bar (0) mesons produced in e(+)e(-) annihilations near threshold. In this work, doubly-tagged D-0(D) over bar (0) events, where one D decays to a CP eigenstate and the other D decays in a semileptonic mode, are reconstructed using a data sample of 2.92 fb(-1) collected with the BESIII detector at the center-of-mass energy of root s = 3.773 GeV. We obtain y(CP) = (-2.0 +/- 1.3 +/- 0.7)%, where the first uncertainty is statistical and the second is systematic. This result is compatible with the current world average.

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• Artikel i tidskrift

Adlarsona, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Measurement of the np -> np pi(0)pi(0) reaction in search for the recently observed d* (2380) resonance

Ingår i Physics Letters B, s. 325-332, 2015.

#### Abstract

Exclusive measurements of the quasi-free np --> np pi(0)pi(0) reaction have been performed by means of dp collisions at T-d = 2.27 GeV using the WASA detector setup at COSY. Total and differential cross sections have been obtained covering the energy region root s = (2.35-2.46) GeV, which includes the region of the ABC effect and its associated d* (2380) resonance. Adding the d* resonance amplitude to that for the conventional processes leads to a reasonable description of the data. The observed resonance effect in the total cross section is in agreement with the predictions of Faldt and Wilkin as well with those of Albadajedo and Oset. The ABC effect, i.e. the low-mass enhancement in the pi(0)pi(0)-invariant mass spectrum, is found to be very modest - if present at all, which might pose a problem to some of its interpretations.

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• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of chi(cJ) decaying into phi K*(892)(K)over-bar

Ingår i Physical Review D, 2015.

#### Abstract

Using a data sample of 106 million psi(3686) events collected with the BESIII detector operated at the BEPCII storage ring, we study for the first time the decays chi(cJ) -> phi(KSK +/-)-K-0 pi(-/+) and chi(cJ) -> phi K+K-pi(0) in the E1 radiative transition psi(3686) -> gamma chi(cJ). The decays are dominated by the three-body decay chi(cJ) -> phi K*(892)(K) over bar. We measure branching fractions for this reaction via the neutral and charged K*(892) and find them consistent with each other within the expectation of isospin symmetry. In the K (K) over bar pi invariant mass distribution, a structure near the K*(892)(K) over bar mass threshold is observed, and the corresponding mass and width are measured to be 1412 +/- 4(stat) +/- 8(sys) MeV/c(2) and Gamma = 84 +/- 12(stat) +/- 40(sys) MeV, respectively. The observed state favors an assignment to the h(1)(1380), considering its possible J(PC) and comparing its mass, width and decay mode to those reported in the Particle Data Group.

• Artikel i tidskrift

Egea Canet, F. J.; Houarner, C.; Boujrad, A.; Gonzalez, V. et al.

### Digital Front-End Electronics for the Neutron Detector NEDA

Ingår i IEEE Transactions on Nuclear Science, s. 1063-1069, 2015.

#### Abstract

This paper presents the design of the NEDA (Neutron Detector Array) electronics, a first attempt to involve the use of digital electronics in large neutron detector arrays. Starting from the front-end modules attached to the PMTs (PhotoMultiplier Tubes) and ending up with the data processing workstations, a comprehensive electronic system capable of dealing with the acquisition and pre-processing of the neutron array is detailed. Among the electronic modules required, we emphasize the front-end analog processing, the digitalization, digital pre-processing and communications firmware, as well as the integration of the GTS (Global Trigger and Synchronization) system, already used successfully in AGATA (Advanced Gamma Tracking Array). The NEDA array will be available for measurements in 2016.

• Artikel i tidskrift

Egea Canet, F. J.; Gonzalez, V.; Tripon, M.; Jastrzab, M. et al.

### A New Front-End High-Resolution Sampling Board for the New-Generation Electronics of EXOGAM2 and NEDA Detectors

Ingår i IEEE Transactions on Nuclear Science, s. 1056-1062, 2015.

#### Abstract

This paper presents the final design and results of the FADC Mezzanine for the EXOGAM (EXOtic GAMma array spectrometer) and NEDA (Neutron Detector Array) detectors. The measurements performed include those of studying the effective number of bits, the energy resolution using HP-Ge detectors, as well as timing histograms and discrimination performance. Finally, the conclusion shows how a common digitizing device has been integrated in the experimental environment of two very different detectors which combine both low-noise acquisition and fast sampling rates. Not only the integration fulfilled the expected specifications on both systems, but it also showed how a study of synergy between detectors could lead to the reduction of resources and time by applying a common strategy.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the proton form factor by studying e(+)e(-) -> p(p)over-tilde

Ingår i Physical Review D, 2015.

#### Abstract

Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of e(+)e(-) -> p (p) over tilde at 12 center-of-mass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal (vertical bar G(E)vertical bar = vertical bar G(M)vertical bar). In addition, the ratio of electric to magnetic form factors, vertical bar G(E)/G(M)vertical bar, and vertical bar G(M)vertical bar are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at root s = 2232.4 and 2400.0 MeV and a combined sample at root s = 3050.0, 3060.0 and 3080.0 MeV, respectively. The measured cross sections are in agreement with recent results from BABAR, improving the overall uncertainty by about 30%. The vertical bar G(E)/G(M)vertical bar ratios are close to unity and consistent with BABAR results in the same q(2) region, which indicates the data are consistent with the assumption that vertical bar G(E)vertical bar = vertical bar G(M)vertical bar within uncertainties.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the e(+)e(-) -> eta J/psi cross section and search for e(+)e(-) -> pi(0)J/psi at center-of-mass energies between 3.810 and 4.600 GeV

Ingår i Physical Review D, 2015.

#### Abstract

Using data samples collected with the BESIII detector operating at the BEPCII collider at 17 center-of-mass energies from 3.810 to 4.600 GeV, we perform a study of e(+)e(-) -> eta J/psi and pi(0)J/psi The Born cross sections of these two processes are measured at each center-of-mass energy. The measured energy-dependent Born cross section for e(+)e(-) -> eta J/psi shows an enhancement around 4.2 GeV. The measurement is compatible with an earlier measurement by Belle.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurements of psi(3686) -> K-Lambda(Xi)over-bar(+) + c.c. and psi(3686) -> gamma K-Lambda(Xi)over-bar(+) + c.c.

Ingår i Physical Review D, 2015.

#### Abstract

Using a sample of 1.06 x 10(8) psi(3686) events produced in e(+)e(-) collisions at root s = 3.686 GeV and collected with the BESIII detector at the BEPCII collider, we present studies of the decays psi(3686) -> K-Lambda(Xi) over bar (+) + c.c. and psi(3686) -> gamma K-Lambda(Xi) over bar (+) + c.c. We observe two hyperons, Xi(1690)(-) and Xi(1820)(-), in the K-Lambda invariant mass distribution in the decay psi(3686) -> K-Lambda(Xi) over bar (+) + c.c. with significances of 4.9 sigma and 6.2 sigma, respectively. The branching fractions of psi(3686) -> K-Lambda(Xi) over bar (+) + c.c., psi(3686) -> K-Sigma(0)(Xi) over bar (+) + c.c, psi(3686) -> gamma chi cJ -> gamma K-Lambda(Xi) over bar (+) + c.c (J = 0, 1, 2), and psi(3686) -> Xi(1690/1820)(-)(Xi) over bar (+) + c.c with sub-sequent decay Xi(1690/1820)(-) -> K-Lambda are measured for the first time.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of the electromagnetic doubly OZI-suppressed decay J/psi -> phi pi(0)

Ingår i Physical Review D, 2015.

#### Abstract

Using a sample of 1.31 billion J/psi events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay J/psi -> phi pi(0), which is the first evidence for a doubly Okubo-Zweig-Iizuka suppressed electromagnetic J/psi decay. A clear structure is observed in the K+K- mass spectrum around 1.02 GeV/c(2), which can be attributed to interference between J/psi -> phi pi(0) and J/psi -> K+K- pi(0) decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of J/psi -> phi pi(0) are [2.94 +/- 0.16(stat) +/- 0.16(syst)] x 10(-6) and [1.24 +/- 0.33(stat) +/- 0.30(syst)] x 10(-7).

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of B(psi(3770) -> gamma chi(c1)) and search for psi(3770) -> gamma chi(c2)

Ingår i Physical Review D, 2015.

#### Abstract

We report a measurement of the branching fraction for psi(3770) -> gamma chi(c1) and search for the transition psi(3770) -> gamma chi(c2) based on 2.92 fb(-1) of e(+)e(-) data accumulated at root s = 3.773 GeV with the BESIII detector at the BEPCII collider. We measure B(psi(3770) -> gamma chi(c1)) = (2.48 +/- 0.15 +/- 0.23) x 10(-3), which is the most precise measurement to date. The upper limit on the branching fraction of psi(3770) -> gamma chi(c2) at a 90% confidence level is B(psi(3770) -> gamma chi(c2)) < 0.64 x 10(-3). The corresponding partial widths are Gamma(psi(3770) -> gamma chi(c1)) = (67.5 +/- 4.1 +/- 6.7)keV and Gamma(psi(3770) -> gamma chi(c2)) < 17.4 keV.

• Artikel i tidskrift

### Studies of the omega Meson with the KLOE Detector

Ingår i Acta Physica Polonica B, s. 53-58, 2015.

#### Abstract

The paper presents status of three studies involving the omega meson using data collected by the KLOE detector. The first two projects are feasibility studies performed on simulated data concerning an upper limit measurement of BR (phi -> omega gamma)and the form factor measurement in the omega -> pi(0)l(+)l(-) Dalitz decay. The third study shows the effect pi(0)-pi(0) interference has in the omega -> pi(+)pi(-)pi(0) Dalitz plot when omega is produced through the e(+)e(-) -> omega pi(0) channel.

• Artikel i tidskrift

Balkestahl, Li Caldeira

### Study of the Dalitz Plot of the η → π+π−π0 Decay with the KLOE Detector

Ingår i Acta Physica Polonica B, s. 31-37, 2015.

#### Abstract

The decay eta -> pi(+)pi(-)pi(0) is studied with the KLOE detector, at the DA Phi NE e(+)e(-) collider. Using a data sample corresponding to an integrated luminosity of 1.6 fb(-1), a new study of the Dalitz plot is presented.

• Artikel i tidskrift

Grzonka, D.; Kilian, K.; Ritman, J.; Sefzick, T. et al.

### Search for Polarization Effects in the Antiproton Production Process

Ingår i Acta Physica Polonica B, s. 191-201, 2015.

#### Abstract

For the production of a polarized antiproton beam, various methods have been suggested including the possibility that antiprotons may be produced polarized which will be checked experimentally. The polarization of antiprotons produced under typical conditions for antiproton beam preparation will be measured at the CERN/PS. If the production process creates some polarization, a polarized antiproton beam could be prepared by a rather simple modification of the antiproton beam facility. The detection setup and the expected experimental conditions are described.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Precision measurement of the D*(0) decay branching fractions

Ingår i Physical Review D, 2015.

#### Abstract

Using 482 pb(-1) of data taken at root s = 4.009 GeV, we measure the branching fractions of the decays of D*(0) into D-0 pi(0) and D-0 gamma to be B(D*(0) -> D-0 pi(0)) = (65.5 +/- 0.8 +/- 0.5)% and B(D*(0) -> D0 gamma) = (34.5 +/- 0.8 +/- 0.5)%, respectively, by assuming that the D*(0) decays only into these two modes. The ratio of the two branching fractions is B(D*(0) -> D-0 pi(0))/B(D*(0) -> D-0 gamma) = 1.90 +/- 0.07 +/- 0.05, which is independent of the assumption made above. The first uncertainties are statistical and the second ones systematic. The precision is improved by a factor of 3 compared to the present world average values.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### ABC effect and resonance structure in the double-pionic fusion to He-3

Ingår i Physical Review C. Nuclear Physics, s. 015201-, 2015.

#### Abstract

Exclusive and kinematically complete measurements of the double pionic fusion to He-3 have been performed in the energy region of the so-called ABC effect, which denotes a pronounced low-mass enhancement in the pi pi-invariant mass spectrum. The experiments were carried out with the WASA detector setup at COSY (the cooler synchrotron at Forschungszentrum Julich). Similar to the observations in the basic pn -> d pi(0)pi(0) reaction and in the dd -> He-4 pi(0)pi(0) reaction, the data reveal a correlation between the ABC effect and a resonance-like energy dependence in the total cross section. Differential cross sections are well described by the hypothesis of d* resonance formation during the reaction process in addition to the conventional t-channel Delta Delta mechanism. The deduced d* resonance width can be understood from collision broadening due to Fermi motion of the nucleons in initial and final nuclei.

• Artikel i tidskrift

Modamio, V.; Valiente-Dobon, J. J.; Jaworski, G.; Hueyuek, T. et al.

### Digital pulse-timing technique for the neutron detector array NEDA

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 71-76, 2015.

#### Abstract

A new digital pulse-timing algorithm, to be used with the future neutron detector array NEDA, has been developed and tested. The time resolution of four 5 in diameter photomultiplier tubes (XP4512, R4144, R11833-100, and ET9390-kb), coupled to a cylindrical 5 in by 5 in BC501A liquict scintillator detector was measured by employing digital sampling electronics and a constant fraction discriminator (CFD) algorithm. The zero crossing of the CM algorithm was obtained with a cubic spline interpolation, which was continuous up to the second derivative. The performance of the algorithm was studied at sampling rates of 500 MS/s and 200 MS/s. The time resolution obtained with the digital electronics was compared to the values acquired with a standard analog CFD. The result of this comparison shows that the time resolution from the analog and the digital measurements at 500 MS/s and at 200 MS/s are within 15% for all the tested photomultiplier tubes.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of the Dalitz decay eta ' -> gamma e(+)e(-)

Ingår i Physical Review D, 2015.

#### Abstract

We report the first observation of the Dalitz decay eta' -> gamma e(+)e(-), based on a data sample of 1.31 billion J/psi events collected with the BESIII detector. The eta' mesons are produced via the J/psi -> gamma eta' decay process. The ratio (eta' -> gamma e(+)e(-))/Gamma (eta' -> gamma gamma) is measured to be (2.13 +/- 0.09(stat) +/- 0.07(sys)) x 10(-2). This corresponds to a branching fraction B(eta' -> gamma e(+)e(-)) = (4.69 +/- 0.20(stat) +/- 0.23(sys)) x 10(-4). The transition form factor is extracted and different expressions are compared to the measured dependence on the e(+)e(-) invariant mass. The results are consistent with the prediction of the vector meson dominance model.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of the Psi(1(3)D(2)) State in e(+)e(-) -> pi(+)pi(-)gamma chi(c1) at BESIII

Ingår i Physical Review Letters, 2015.

#### Abstract

We report the observation of the X(3823) state in the process e(+)e(-) -> pi(+)pi(-) X(3823) pi(+)pi(-)gamma chi(c1) with a statistical significance of 6.2 sigma, in data samples at center-of-mass energies root s = 4.230, 4.260, 4.360, 4.420, and 4.600 GeV collected with the BESIII detector at the BEPCII electron positron collider. The measured mass of the X(3823) state is (3821.7 +/- 1.3 +/- 0.7) MeV/c(2), where the first error is statistical and the second systematic, and the width is less than 16 MeV at the 90% confidence level. The products of the Born cross sections for e(+)e(-) -> pi(+)pi(-) X(3823) and the branching ratio B [X(3823) -> gamma X-c1c2] are also measured. These measurements are in good agreement with the assignment of the X(3823) state as the Psi(1(3)D(2)) charmonium state.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Evidence for e(+)e(-)->gamma chi c1,2 at center-of-mass energies from 4.009 to 4.360 GeV

Ingår i Chinese Physics C, High Energy Physics & Nuclear Physics, 2015.

#### Abstract

Using data samples collected at center-of-mass energies of root s=4.009, 4.230, 4.260, and 4.360 GeV with the BESIII detector operating at the BEPCII collider, we perform a search for the process e(+)e(-)->gamma chi(cJ) (J=0, 1, 2) and find evidence for e(+)e(-)->gamma chi(c1) and e(+)e(-)->gamma chi(c2) with statistical significances of 3.0 sigma and 3.4 sigma, respectively. The Born cross sections sigma(B)(e(+)e(-)->gamma chi(cJ)), as well as their upper limits at the 90% confidence level (C.L.) are determined at each center-of-mass energy.

• Artikel i tidskrift

Babusci, D.; Balwierz-Pytko, I.; Bencivenni, G.; Bloise, C. et al.

### Study of the Dalitz decay phi -> eta e(+)e(-) with the KLOE detector

Ingår i Physics Letters B, s. 1-6, 2015.

#### Abstract

We have studied the vector to pseudoscalar conversion decay phi -> eta e(+)e(-), with.. eta -> pi(0)pi(0)pi(0), with the KLOE detector at DA phi NE. The data set of 1.7 fb(-1) of e(+)e(-) collisions at root s similar to M-phi contains a clear conversion decay signal of similar to 31,000 events from which we measured a value of BR(phi -> eta e(+)e-) = (1.075 +/- 0.007 +/- 0.038) x 10(-4). The same sample is used to determine the transition form factor by a fit to the e(+)e(-) invariant mass spectrum, obtaining b(phi eta)=( 1.28 +/- 0.10(-0.08)(+0.09)) GeV-2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.

Open access
• Artikel i tidskrift

Crespi, F. C. L.; Bracco, A.; Nicolini, R.; Lanza, E. G. et al.

### 1(-) and 2(+) discrete states in Zr-90 populated via the (O-17, O-17 'gamma) reaction

Ingår i Physical Review C. Nuclear Physics, 2015.

#### Abstract

2(+) and 1(-) states in Zr-90 were populated via the (O-17, O-17 'gamma) reaction at 340 MeV. The gamma decay was measured with high resolution using the AGATA (advanced gamma tracking array demonstrator array). Differential cross sections were obtained at few different angles for the scattered particle. The results of the elastic scattering and inelastic excitation of 2(+), 3(,)(-) and 1(-) states are compared with distorted-wave Born approximation (DWBA) calculations, using both the standard collective form factor and a form factor obtained by folding microscopically calculated transition densities. This allowed to extract the isoscalar component of the 1(-) state at 6.424 MeV. The comparison of the present (17O, 17O 'gamma) data with existing (gamma,gamma') and (p, p') data in the corresponding region of the gamma continuum (6-11 MeV), characterized by a large E1 component, shows completely different behaviors of the cross section as a function of the nuclear excitation energy. The comparison of the data with DWBA calculations suggests a decrease of the isoscalar strength in the cross section with increasing excitation energy.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the $D\to K^-\pi^+$ strong phase difference in $\psi(3770)\to D^0\overline{D}{}^0$

Ingår i PHYSICS LETTERS B, 2014.

#### Abstract

We study $D^0\overline{D}{}^0$ pairs produced in $e^+e^-$ collisions at $\sqrt{s}=3.773$ GeV using a data sample of 2.92 fb$^{-1}$ collected with the BESIII detector. We measure the asymmetry $\mathcal{A}^{CP}_{K\pi}$ of the branching fractions of $D \to K^-\pi^+$ in $CP$-odd and $CP$-even eigenstates to be $(12.7\pm1.3\pm0.7)\times10^{-2}$. $\mathcal{A}^{CP}_{K\pi}$ can be used to extract the strong phase difference $\delta_{K\pi}$ between the doubly Cabibbo-suppressed process $\overline{D}{}^{0}\to K^-\pi^+$ and the Cabibbo-favored process $D^0\to K^- \pi^+$. Using world-average values of external parameters, we obtain $\cos\delta_{K\pi} = 1.02\pm0.11\pm0.06\pm0.01$. Here, the first and second uncertainties are statistical and systematic, respectively, while the third uncertainty arises from the external parameters. This is the most precise measurement of $\delta_{K\pi}$ to date.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of electromagnetic Dalitz decays J/\psi \to P e^+e^-

Ingår i PHYSICAL REVIEW D, 2014.

#### Abstract

Based on a sample of (225.3\pm2.8)\times 10^{6} J/\psi events collected with the BESIII detector, the electromagnetic Dalitz decays of J/\psi \to P e^+e^-(P=\eta'/\eta/\pi^0) are studied. By reconstructing the pseudoscalar mesons in various decay modes, the decays J/\psi \to \eta' e^+e^-, J/\psi \to \eta e^+e^- and J/\psi \to \pi^0 e^+e^- are observed for the first time. The branching fractions are determined to be \mathcal{B}(J/\psi\to \eta' e^+e^-) = (5.81\pm0.16\pm0.31)\times10^{-5}, \mathcal{B}(J/\psi\to \eta e^+e^-) = (1.16\pm0.07\pm0.06)\times10^{-5}, and \mathcal{B}(J/\psi\to \pi^0 e^+e^-)=(7.56\pm1.32\pm0.50)\times10^{-7}, where the first errors are statistical and the second ones systematic.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Precision measurements of $B(D^+ \rightarrow \mu^+ \nu_{\mu})$, the pseudoscalar decay constant $f_{D^+}$, and the quark mixing matrix element $|V_{\rm cd}|$

Ingår i PHYSICAL REVIEW D, 2014.

#### Abstract

We report a measurement of the branching fraction $B(D^+ \rightarrow \mu^+ \nu_{\mu}) = [3.71 \pm 0.19 (\rm stat) \pm 0.06 (\rm sys)]\times 10^{-4}$ based on 2.92 ${\rm fb^{-1}}$ of data accumulated at $\sqrt{s}=3.773$ GeV with the BESIII detector at the BEPCII collider. This measurement, in conjunction with the Cabibbo-Kobayashi-Maskawa matrix element $|V_{\rm cd}|$ determined from a global Standard Model fit, implies a value for the weak decay constant $f_{D^+}=(203.2 \pm 5.3 \pm 1.8)$ MeV. Additionally, using this branching fraction measurement together with a Lattice QCD prediction for $f_{D^+}$, we find $|V_{\rm cd}|=0.2210\pm 0.0058 \pm 0.0047$. In either case, these are the most precise results for these quantities to date.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of $e^+e^− → γX$(3872) at BESIII

Ingår i PHYSICAL REVIEW LETTERS, 2014.

#### Abstract

With data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.009 to 4.420 GeV, the process $e^{+} e^{-} \to \gamma X(3872)$ is observed for the first time with a statistical significance of $6.3\sigma$. The measured mass of the $X(3872)$ is ($3871.9\pm 0.7_{\rm stat.}\pm 0.2_{\rm sys.}$) MeV/$c^2$, in agreement with previous measurements. Measurements of the product of the cross section $\sigma[e^{+} e^{-} \to \gamma X(3872)]$ and the branching fraction $\mathcal{B}[X(3872) \to \pi^{+} \pi^{-} J/\psi]$ at center-of-mass energies 4.009, 4.229, 4.260, and 4.360 GeV are reported. Our measurements are consistent with expectations for the radiative transition process $Y(4260) \to \gamma X(3872)$.

• Artikel i tidskrift

Guastalla, G; DiJulio, D D; GÃ³rska, M; CederkÃ€ll, J et al.

### Analysis and results of the 104 Sn Coulomb excitation experiment

Ingår i Journal of Physics: Conference Series, 2014.

#### Abstract

The analysis of the Coulomb excitation experiment conducted on 104 Sn required a strict selection of the data in order to reduce the large background present in the Î³-ray energy spectra and identify the Î³-ray peak corresponding to the Coulomb excitation events. As a result the B(E2; 0 + â 2 + ) value could be extracted, which established the downward trend towards 100 Sn and therefore the robustness of the N=Z=50 core against quadrupole excitations.

• Konferensbidrag

Schönning, Karin; Thomé, Erik

### Spin observables in antihyperon-hyperon production with PANDA

Ingår i XI International Conference on Hyperons, Charm and Beauty Hadrons (BEACH 2014), s. 012007-, 2014.

#### Abstract

Spin observables provide a powerful tool in understanding the physics. Seven polarisation parameters of the Omega baryon can be extracted from the angular distributions of the hyperon decay and studied with the future PANDA experiment at FAIR. Simulation studies show that strange and single charmed hyperon channels have great prospects with PANDA.

Open access
• Konferensbidrag

Heijkenskjold, Lena; Collaboration, WASA-at-COSY

### Hadronic decays of the omega meson

Ingår i Meson 2014 - 13th International Workshop on Production, Properties and Interaction of Mesons, 2014.

#### Abstract

The WASA-at-COSY collaboration has collected a high statistics data set of. mesons produced through the p + d -> He-3 + omega reaction. This article presents the status of the ongoing studies of two. decay channels. The decay dynamics of the omega -> pi(+)pi(-)pi(0) channel is investigated by means of a Dalitz plot distribution and the omega -> pi(+)pi(-) channel is examined to search for a possible manifestation of rho - omega interference in hadronic production.

• Konferensbidrag

Leupold, Stefan

### Interactions of light mesons with photons

Ingår i Meson 2014 - 13th International Workshop on Production, Properties and Interaction of Mesons, 2014.

#### Abstract

Interactions between hadrons and photons constitute an important tool to explore the intrinsic structure of hadrons. At the same time, high-precision determinations of electromagnetic processes, as in particular g - 2 of the muon, constitute a promising tool to look for the impact of beyond-standard-model physics. Here hadronic contributions constitute the main uncertainty for the standard-model prediction. In this talk results for electromagnetic transition form factors and two-gamma amplitudes are presented.

• Konferensbidrag

Pyszniak, Andrzej; Calén, Hans; Fransson, Kjell E. I.; Hejny, V. et al.

### Studies on implementation of pellet tracking in hadron physics experiments

Ingår i Meson 2014 - 13th International Workshop on Production, Properties and Interaction of Mesons, 2014.

#### Abstract

A system for optical tracking of frozen hydrogen microsphere targets (pellets) has been designed. It is intended for the upcoming hadron physics experiment PANDA at FAIR, Darmstadt, Germany. With such a tracking system one can reconstruct the positions of the individual pellets at the time of a hadronic interaction in the offline event analysis. This gives information on the position of the primary interaction vertex with an accuracy of a few 100 mu m, which is very useful e.g. for reconstruction of charged particle tracks and secondary vertices and for background suppression. A study has been done at the WASA detector setup (Forschungszentrum Julich, Germany) to check the possibility of classification of hadronic events as originating in pellets or in background. The study has been done based on the instantaneous rate a Long Range TDC which was used to determine if a pellet was present in the accelerator beam region. It was clearly shown that it is possible to distinguish the two event classes. Also, an experience was gained with operation of two synchronized systems operating in different time scales, as it will also be the case with the optical pellet tracking.

• Artikel i tidskrift

Ma, Binsong; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### A new method for electron momentum reconstruction in the PANDA experiment

Ingår i Journal of Physics, Conference Series, 2014.

#### Abstract

The Kalman Filter in existing PANDARoot framework of experiment is not optimally suited for electrons, for which the highly non-Gaussian Bremsstrahlung process yields a tail in the momentum resolution distribution. A new method was therefore developed to improve the electron momentum reconstruction with an event by event procedure. The improvements of the electron momentum resolution will be shown. The interest of the method for the electromagnetic channels studies will also be presented.

• Artikel i tidskrift

Fioravanti, Elisa; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Experimental overview of the PANDA experiment

Ingår i Journal of Physics, Conference Series, 2014.

#### Abstract

The physics program of the (anti-Proton ANhiliation ar DArmstadt) experiment will address various questions related to the strong interactions by employing a multi-purpose detector system at the High Energy Storage Ring (HESR) for anti-protons of the upcoming Facility for Anti-proton and Ion Research (FAIR). The excellent antiproton beam resolution of Δp/p ~ 10−5 and the high luminosity =2×1032cm−2 s−1 will allow the precise measurement of the charmonium and open charm spectroscopy, the search for exotic hadrons like multiquarks, glueballs and hybrids, the study of in-medium modifications of hadrons and the nucleon structure.

• Artikel i tidskrift

Mertens, Marius; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Triplet based online track finding in the PANDA-STT

Ingår i Journal of Physics, Conference Series, 2014.

#### Abstract

The PANDA-Experiment at the future FAIR facility in Darmstadt will study antiproton-proton collisions in a fixed-target setup with a phase-space cooled antiproton beam with a momentum from 1.5 to 15 GeV/c at a nominal interaction rate of 2 · 107 s−1. The data acquisition of the detectors has to run in a triggerless mode and the physics events of interest are identified by an online event filter. Tracking information is a key input for the event filter to distinguish signal events from background. A variety of tracking algorithms is foreseen to process the different track topologies. The so-called Triplet Finder, which is presented here, is a track finding algorithm based on the central straw tube tracker (STT) of PANDA. The algorithm focuses on mathematical simplicity and robustness to allow an online processing of the incoming detector hits. The algorithm and results of a proof-of-concept implementation are presented.

• Artikel i tidskrift

Tomasi-Gustafsson, Egle; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Electromagnetic proton form factors: perspectives for PANDA

Ingår i EPJ Web of Conferences, 2014.

• Artikel i tidskrift

Boca, Gianlugi; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The PANDA experiment: physics goals and experimental setup

Ingår i EPJ Web of Conferences, 2014.

• Artikel i tidskrift

Destefanis, Marco; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Spin studies via Drell-Yan processes at PANDA

Ingår i EPJ Web of Conferences, 2014.

#### Abstract

The nucleon structure is still not completely understood. A transverse momentum dependent description of the nucleon structure is a crucial milestone for several forthcoming studies in a wide range of experimental scenarios. By means of antiproton beams, possibly polarized in a later stage of the project, with a beam momentum up to 15 GeV/c, which will be available at the future FAIR facility, the nonperturbative region of QCD is planned to be investigated. One of the main goals of the forthcoming experiments at FAIR is the study of Drell-Yan lepton pairs by means of proton-antiproton annihilations, taking also advantage of the expected high luminosity. The Drell-Yan production is a unique tool to access the spin dependent properties of the nucleon, and in particular its transverse degrees of freedom. Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs), i.e. the Boer-Mulders function, the Sivers function, and the Transversity, could be deeply investigated by means of experimental angular asymmetries. In later stages of FAIR, single- and double-spin asymmetries could be investigated as well. The Drell-Yan physics program which could be accessed at FAIR with the PANDA experiment will be discussed in details, in the light of existing results in the field.

• Artikel i tidskrift

Sanchez Lorente, Alicia; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Hypernuclear physics studies of the PANDA experiment at FAIR

Ingår i Hyperfine Interactions, 2014.

#### Abstract

Spin observables provide a powerful tool in understanding the physics. Seven polarisation parameters of the Ω baryon can be extracted from the angular distributions of the hyperon decay and studied with the future PANDA experiment at FAIR. Simulation studies show that strange and single charmed hyperon channels have great prospects with PANDA.

• Artikel i tidskrift

Atomassa, Ermias; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Feasibility studies for nucleon structure measurements with PANDA

Ingår i EPJ Web of Conferences, 2014.

#### Abstract

The study of nucleon structure is one of the main physics goals of PANDA to be built at the FAIR accelerator complex. The excellent particle identification performance of the PANDA detector will enable measurements of exclusive channels p&#772; p -> e^+e^- and p&#772; p -> pi^0 J/psi -> pi^0e^+e^- to extract the electromagnetic form factors of protons and pi-nucleon Transition Distribution Amplitudes (pi-N TDAs). After a brief description of the PANDA apparatus and a method to handle momentum resolution degradation due to Bremsstrahlung, the physics of pi-N TDAs is discussed. An estimate for the expected signal to background ratio for p&#772; p -> pi^0 J/psi -> pi^0e^+e^- that takes into account the main background source is given.

• Konferensbidrag

Balkeståhl, Li Caldeira

### Dalitz plot analysis for eta -> pi(+)pi(-)pi(0) at KLOE

Ingår i Menu 2013 - 13Th International Conference Meson-Nucleon Physics And The Structure Of The Nucleon, 2014.

#### Abstract

Based on 1.6 fb(-1) of data taken with the KLOE detector at the DA phi NE phi-factory, we present the status of the ongoing analysis of the eta -> pi(+)pi(-)pi(0) Dalitz plot. With 4.48 . 10(6) events in the Dalitz plot, the preliminary results for the Dalitz plot parameters are: a = 1.104(3), b = 0.144(3), d = 0.073(3) and f = 0.155(6).

Open access
• Konferensbidrag

Terschlüsen, Carla; Strandberg, Bruno; Leupold, Stefan

### Reactions with pions and vector mesons in the sector of odd intrinsic parity

Ingår i Menu 2013 - 13Th International Conference Meson-Nucleon Physics And The Structure Of The Nucleon, 2014.

#### Abstract

In chiral perturbation theory, the leading-order contribution to reactions with pions in the sector of odd intrinsic parity is defined by the Wess-Zumino-Witten structure. This structure is supplemented by a simple vector-meson Lagrangian where the vector mesons are described by antisymmetric tensor fields. With the rho-omega-pion coupling as the only parameter in the sector of odd intrinsic parity, i.e. without additional contact terms, one can achieve a proper description of the pion transition form factor and the three-pion production in electron-positron collisions.

Open access
• Konferensbidrag

Balkeståhl, Li Caldeira

### Dalitz Plot analysis for eta -> pi(+)pi(-)pi(0) at KLOE

Ingår i INPC 2013 - International Nuclear Physics Conference, Vol. 2, s. 06003-, 2014.

#### Abstract

We present the status of an ongoing analysis of the eta -> pi(+)pi(-)pi(0) Dalitz plot, as well as preliminary results for the Dalitz plot parameters. The analysis is based on data taken at the DA Phi NE phi-factory with the KLOE detector.

Open access
• Konferensbidrag

Terschlusen, Carla; Leupold, Stefan; Strandberg, Bruno

### Low-lying pseudoscalar and vector mesons and their dynamics: How to describe radiative reactions with an odd number of pions

Ingår i INPC 2013 - International Nuclear Physics Conference, Vol. 2, s. 06023-, 2014.

#### Abstract

In chiral perturbation theory, the leading-order contribution to reactions with pions in the sector of odd intrinsic parity is defined by the Wess-Zumino-Witten structure. This structure is supplemented by a simple vector-meson Lagrangian where the vector mesons are described by antisymmetric tensor fields. With the rho-omega-pion coupling as the only parameter in the sector of odd intrinsic parity, i.e. without additional contact terms, one can achieve a proper description of the single- and double-virtual pion transition form factor and the three-pion production in electron-positron collisions.

Open access
• Artikel i tidskrift

Iazzi, Felice; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Doubly strange system physics with antiprotons at PANDA

Ingår i EPJ Web of Conferences, 2014.

#### Abstract

The study of the doubly strange hyper-systems represents a step forward in understanding the unexplored world of the strange matter in the frame of a better knowledge of the hyperon-nucleon and hyperon-nucleus interaction. The production of double hyper-systems, up to now, have been based on the use of kaon beams through a double strangeness exchange reaction. A new technique has been designed by the PANDA Collaboration, which will use the antiprotons at 3 GeV/c of the HESR facility at FAIR to create doubly strange hyperons and drive them into nuclear targets. This technique requires the use of 2 targets, located inside and outside the beam pipe. In spite of the constraints arising from the presence of a solid target inside an antiproton ring, the technique looks promising in terms of rate of hyperons and hyper-nuclei produced. After a review of the physics items that will be investigated in the hyper-nuclear section of PANDA experiment, the characteristics of the antiprotons facility, the results of the feasibility study of the 2-target technique, the design of the hyper-nuclear set-up in PANDA and the expected rates of the double hyper-nuclei will be presented.

• Konferensbidrag

Schönning, Karin; Thomé, Erik

### Antihyperon-hyperon production in antiproton-proton annihilations with PANDA

Ingår i FAIRNESS 2013, s. 012013-, 2014.

#### Abstract

Hyperon production is an excellent probe of the strong interaction in the confinement domain. The spin observables provide a powerful tool in understanding the underlying physical processes. Expressions of the seven non-zero polarisation parameters of the Omega baryon from decay angular distributions have recently been derived by the Uppsala group. Simulation studies show that all strange and single charmed hyperon production channels have great prospects with the PANDA detector.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for the weak decays J/psi -> D-s(()*()-) e(+)nu(e) + c.c.

Ingår i Physical Review D, s. 112014-, 2014.

#### Abstract

Using a sample of 2.25 x 10(8) J/psi events collected with the BESIII detector at the BEPCII collider, we search for the J/psi semileptonic weak decay J/psi -> D-s(-) e(+)nu(e) +c.c. with a much higher sensitivity than previous searches. We also perform the first search for J/psi -> D-s(*-) e(+) nu(e) + c.c. No significant excess of a signal above background is observed in either channel. At the 90% confidence level, the upper limits are determined to be B(J/psi -> D-s(-) e(+) nu(e) + c.c.) < 1.3 x 10(-6) and B(J/psi -> D-s*(-) e(+) nu(e) + c.c.) < 1.8 x 10(-6), respectively. Both are consistent with Standard Model predictions.

• Artikel i tidskrift

Jokhovets, L.; Drochner, M.; Erven, A.; Erven, W. et al.

### ADC-Based Real-Time Signal Processing for the PANDA Straw Tube Tracker

Ingår i IEEE Transactions on Nuclear Science, s. 3627-3634, 2014.

#### Abstract

The PANDA (AntiProton Annihilations at Darmstadt) experiment is being built at the new Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. PANDA will measure antiproton-proton annihilation reactions in the charm quark mass range to investigate the nature of the strong interaction. This particle physics experiment will run at very high reaction rates of 10-20 MHz. Our work is related to an ADC (analog-to-digital converter) based data acquisition system for the PANDA Straw Tube Tracker (STT). The STT will be able to deliver data rates up to 20 GByte/s through over 4600 signal channels and could require major efforts for the hardware implementation as well as high offline processing power. Test beam studies were carried out in order to specify a proper system architecture with feasible hardware and to reduce output data stream to a level suitable for offline processing. We analyze the strawtube response to both the proton beam and irradiation. Furthermore, we present real-time processing using the neighboring straw information and introduce the technique to reconstruct the tracks.

• Artikel i tidskrift

Hoferichter, M.; Kubis, B.; Leupold, Stefan; Niecknig, F. et al.

### Dispersive analysis of the pion transition form factor

Ingår i European Physical Journal C, s. 3180-, 2014.

#### Abstract

We analyze the pion transition form factor using dispersion theory. We calculate the singly-virtual form factor in the time-like region based on data for the e(+) e(-) -> 3 pi cross section, generalizing previous studies on omega, phi -> 3 pi decays and gamma pi -> pi pi scattering, and verify our result by comparing to e(+) e(-) -> pi(0)gamma. data. We perform the analytic continuation to the space-like region, predicting the poorly-constrained space-like transition form factor below 1GeV, and extract the slope of the form factor at vanishing momentum transfer a(pi) = (30.7 +/- 0.6) x10(-3). We derive the dispersive formalism necessary for the extension of these results to the doubly-virtual case, as required for the pion-pole contribution to hadronic light-by-light scattering in the anomalous magnetic moment of the muon.

Open access
• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Evidence for a New Resonance from Polarized Neutron-Proton Scattering

Ingår i Physical Review Letters, s. 202301-, 2014.

#### Abstract

Exclusive and kinematically complete high-statistics measurements of quasifree polarized (n) over right arrowp scattering have been performed in the energy region of the narrow resonancelike structure d* with I(J(P)) = 0(3(+)),M approximate to 2380 MeV, and Gamma approximate to 70 MeV observed recently in the double-pionic fusion channels pn -> d pi(0)pi(0) and pn -> d pi(+)pi(-). The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process (d) over right arrowp -> np + p(spectator). This allowed the np analyzing power, A(y), to be measured over a broad angular range. The obtained A(y) angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new A(y) data into the SAID analysis produces a pole in the D-3(3) - (3)G(3) waves in support of the d* resonance hypothesis.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Amplitude analysis of the D+ -> K-S(0)pi + (0)(pi) Dalitz plot

Ingår i Physical Review D, s. 052001-, 2014.

#### Abstract

We perform an analysis of the D+ -> K-S(0)pi + (0)(pi) Dalitz plot using a data set of 2.92 fb(-1) of e(+) e(-) collisions at the (3770) mass accumulated by the BESIII experiment, in which 166694 candidate events are selected with a background of 15.1%. The Dalitz plot is found to be well represented by a combination of six quasitwo- body decay channels [k(SP)(0)(+) (1450)(+,) ] plus a small nonresonant component. Using the fit fractions from this analysis, partial branching ratios are updated with higher precision than previous measurements.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for the rare decays J/y -> D-s(-) rho(+) and J/psi -> <(D)over bar(0)<(K)over bar*(0)

Ingår i Physical Review D, s. 071101-, 2014.

#### Abstract

A search for the rare decays of J/psi -> D-S(-) rho(+) + c.c. and J/psi -> <(D)over bar(0)<(K)over bar*(0) + c.c. is performed with a data sample of 225.3-million J/psi events collected with the Beijing Spectrometer III detector. No evident signal is observed. Upper limits on the branching fractions are determined to be beta(J/psi -> D-S(-)rho(+) + c.c.) < 1.3 x 10(-5) and beta(J/psi -> <(D)over bar(0)<(K)over bar*(0) + c.c.) < 2.5 x 10(-6) at the 90% confidence level.

• Artikel i tidskrift

Moradi, F. Ghazi; Cederwall, B.; Qi, C.; Back, T. et al.

### Spectroscopy of the neutron-deficient N=50 nucleus Rh-95

Ingår i Physical Review C. Nuclear Physics, s. 044310-, 2014.

#### Abstract

The neutron-deficient semimagic (neutron number N = 50) Rh-95 nucleus has been produced at high spins using the projectile-target system Ca-40 + Ni-58 at 125 MeV beam energy. The gamma-decays of levels populated by the 3p fusion evaporation reaction channel were studied using gamma-gamma coincidences, and 20 new gamma-ray transitions involving 15 new positive-and negative-parity states were observed. Spin and parity for many of the excited states were firmly deduced for the first time using the combined directional angular correlation and direction-polarization techniques. The observed structures are discussed within the framework of large-scale shell model calculations. E1 transition strengths were deduced and used together with the results of the shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.

• Artikel i tidskrift

Babusci, D.; Balwierz-Pytko, I.; Bencivenni, G.; Bloise, C. et al.

### Test of CPT and Lorentz symmetry in entangled neutral kaons with the KLOE experiment

Ingår i Physics Letters B, s. 89-94, 2014.

#### Abstract

Neutral kaon pairs produced in phi decays in anti-symmetric entangled state can be exploited to search for violation of CPT symmetry and Lorentz invariance. We present an analysis of the CP-violating process phi -> KSKL -> pi(+)pi(-)pi(+)pi(-) based on 1.7 fb(-1) of data collected by the KLOE experiment at the Frascati phi-factory DA Phi NE. The data are used to perform a Measurement of the CPT-violating parameters Delta a(mu) for neutral kaons in the context of the Standard Model Extension framework. The parameters measured in the reference frame of the fixed stars are: Delta a(0) = (-6.0 +/- 7.7(stat)+/- 3.1(syst)) X 10(-18) GeV, Delta a(x) = (0.9 +/- 1.5(stat)+/- 0.6(syst)) X 10(-18) GeV, Delta a(y) = (-2.0 +/- 1.5(stat)+/- 0.5(syst)) X 10(-18) GeV, Delta a(z) = (3.1 +/- 1.7(stat)+/- 0.5(syst)) X 10(-18) GeV. These are presently the most precise measurements in the quark sector of the Standard Model Extension. (C) 2014 The Authors. Published by Elsevier B.V.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Precision measurements of B(D+ -> mu(+)nu(mu)), the pseudoscalar decay constant fD+, and the quark mixing matrix element vertical bar V-cd vertical bar

Ingår i Physical Review D, s. 051104-, 2014.

#### Abstract

We report a measurement of the branching fraction B(D+ -> mu(+)nu(mu)) = [3.71 +/- 0.19(stat) +/- 0.06(sys)] x 10(-4) based on 2.92 fb(-1) of data accumulated at root s = 3.773 GeV with the BESIII detector at the BEPCII collider. This measurement, in conjunction with the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cd vertical bar determined from a global Standard Model fit, implies a value for the weak decay constant f(D+) = (203.2 +/- 5.3 +/- 1.8) MeV. Additionally, using this branching fraction measurement together with a lattice QCD prediction for f(D+), we find vertical bar V-cd vertical bar 0.2210 +/- 0.0058 +/- 0.0047. In either case, these are the most precise results for these quantities to date.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of chi(cJ) decaying into eta ' K+K-

Ingår i Physical Review D, s. 074030-, 2014.

#### Abstract

Using (106.41 +/- 0.86) x 10(6) Psi(3686) events collected with the BESIII detector at BEPCII, we study for the first time the decay chi(cJ) -> eta'K+K- (J = 1, 2), where eta' -> gamma rho(0) and eta' -> eta pi(+)pi(-). A partial wave analysis in the covariant tensor amplitude formalism is performed for the decay chi(c1) -> eta'K+K-. Intermediate processes chi(c1) -> eta'f(2)'(1525) chi(c1) -> K-0*(1430)K-+/-(-/+) (K-0*(1430)(+/-) -> eta'K-+/-) are observed with statistical significances larger than 5 sigma, and their branching fractions are measured.

• Artikel i tidskrift

Ferrario, M.; Alesini, D.; Alessandroni, M.; Anania, M. P. et al.

### IRIDE: Interdisciplinary research infrastructure based on dual electron linacs and lasers

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 138-146, 2014.

#### Abstract

This paper describes the scientific aims and potentials as well as the preliminary technical design of RUDE, an innovative tool for multi-disciplinary investigations in a wide field of scientific, technological and industrial applications. IRIDE will be a high intensity "particles factory", based on a combination of high duty cycle radio-frequency superconducting electron linacs and of high energy lasers. Conceived to provide unique research possibilities for particle physics, for condensed matter physics, chemistry and material science, for structural biology and industrial applications, IRIDE will open completely new research possibilities and advance our knowledge in many branches of science and technology. [RIDE is also supposed to be realized in subsequent stages of development depending on the assigned priorities.

• Artikel i tidskrift

Luo, X. L.; Modamio, V.; Nyberg, Johan; Valiente-Dobon, J. J. et al.

### Test of digital neutron-gamma discrimination with four different photomultiplier tubes for the NEutron Detector Array (NEDA)

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 83-91, 2014.

#### Abstract

A comparative study of the neutron-gamma discrimination performance of a liquid scintillator detector BC501A coupled to four different 5 in photomultiplier tubes (ET9390kb, R11833-100, XP4512 and R4144) was carried out Both the Charge Comparison method and the Integrated Rise-Time method were implemented digitally to discriminate between neutrons and gamma rays emitted by a Cf-252 source. In both methods, the neutron-gamma discrimination capabilities of the four photomultiplier tubes were quantitatively compared by evaluating their figure-of-merit values at different energy regions between 50 keVee and 1000 keVee. Additionally, the results were further verified qualitatively using time-of-flight to distinguish gamma rays and neutrons. The results consistently show that photomultiplier tubes R11833-100 and ET9390kb generally perform best regarding neutron-gamma discrimination with only slight differences in figure-of-merit values. This superiority can be explained by their relatively higher photoelectron yield, which indicates that a scintillator detector coupled to a photomultiplier tube with higher photoelectron yield tends to result in better neutron-gamma discrimination performance. The results of this work will provide reference for the choice of photomultiplier tubes for future neutron detector arrays like NEDA.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of e(+)e(-) -> pi(0)pi(0)h(c) and a Neutral Charmoniumlike Structure Z(c)(4020)(0)

Ingår i Physical Review Letters, s. 212002-, 2014.

#### Abstract

Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider at center-of-mass energies of root s = 4.23, 4.26, and 4.36 GeV, we observe e(+)e(-) -> pi(0)pi(0)h(c) for the first time. The Born cross sections are measured and found to be about half of those of e(+)e(-) -> pi(+)pi(-)h(c) within less than 2 sigma. In the pi(0)h(c) mass spectrum, a structure at 4.02 GeV/c(2) is found. It is most likely to be the neutral isospin partner of the Z(c)(4020)(+/-) observed in the process of e(+)e(-) -> pi(+)pi(-)h(c) being found. A fit to the pi(0)h(c) invariant mass spectrum, with the width of the Z(c)(4020)(0) fixed to that of its charged isospin partner and possible interferences with non-Z(c)(4020)(0) amplitudes neglected, gives a mass of (4023.9 +/- 2.2 +/- 3.8) MeV/c(2) for the Z(c)(4020)(0), where the first error is statistical and the second systematic.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Measurement of the eta -> pi(+)pi(-)pi(0) Dalitz plot distribution

Ingår i Physical Review C. Nuclear Physics, s. 045207-, 2014.

#### Abstract

The Dalitz plot distribution of the eta -> pi(+)pi(-)pi(0) decay is determined by using a data sample of 1.2 x 10(7) eta mesons from the pd -> He-3 eta reaction at 1 GeV collected by the WASA detector at COSY.

• Artikel i tidskrift

Balkeståhl, Li Caldeira; Thome, E.

### Prospects for pp rarr YY studies at PANDA

Ingår i Hyperfine Interactions, s. 79-83, 2014.

#### Abstract

Strangeness and charm production provide an excellent probe of QCD in the confinement domain. With the PANDA detector at FAIR, this can be studied in e.g., hyperon production in the pp rarr YY reactions. In PANDA, all ground state strange hyperons and single charmed Lambda's will be accessible. Simulations show that the differential cross sections and spin observables can be well reconstructed for these reaction channels.

• Artikel i tidskrift

Pyszniak, Andrzej; Calén, Hans; Fransson, Kjell E. I.; Fridén, Carl-Johan et al.

### A pellet tracking system for the PANDA experiment

Ingår i Hyperfine Interactions, s. 159-163, 2014.

#### Abstract

Frozen microspheres of hydrogen (pellets) will be one of the target types for the future hadron physics experiment PANDA at FAIR (GSI, Darmstadt, Germany) [1]. Pellets with a diameter of 25- mum are generated about 3 meters above the interaction region, to which they travel with a velocity around 80 m/s inside a narrow pipe. The interaction region is defined by the overlap of the pellet stream and the accelerator beam and has a size of a few millimeters. One would like to know the interaction point more precisely, to have better possibilities to reconstruct particle tracks and events e.g. in charmonium decay studies. One would also like to suppress background events that do not originate in a pellet, but e.g. may occur in rest gas, that is present in the beam pipe. A solution is provided by the presented pellet tracking system together with a target operation mode that provides one and only one pellet in the interaction region most of the time. The goal is to track individual pellets in order to know their position with a resolution of a few tenths of a millimeter at the time of an interaction. The system must also be highly efficient and provide tracking information for essentially all pellets that pass the interaction region. Presented results from the design studies show that the goals can be fulfilled by this solution.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for C-parity violation in J/psi -> gamma gamma and gamma phi

Ingår i Physical Review D, s. 092002-, 2014.

#### Abstract

Using 1.06 x 10(8) psi(3686) events recorded in e(+)e(-) collisions at root s = 3.686 GeV with the BESIII at the BEPCII collider, we present searches for C-parity violation in J/psi -> gamma gamma and gamma phi decays via psi(3686) -> J/psi pi(+)pi(-). No significant signals are observed in either channel. Upper limits on the branching fractions are set to be B(J/psi -> gamma gamma) < 2.7 x 10(-7) and B(J/psi -> gamma phi) < 1.4 x 10(-6) at the 90% confidence level. The former is one order of magnitude more stringent than the previous upper limit, and the latter represents the first limit on this decay channel.

• Artikel i tidskrift

Babuscih, D.; Balwierz-Pytkog, I.; Bencivenni, G.; Bloise, C. et al.

### Measurement of the absolute branching ratio of the K+ -> pi(+) pi(-) pi(+) (gamma) decay with the KLOE detector

Ingår i Physics Letters B, s. 128-133, 2014.

#### Abstract

The absolute branching ratio of the K+ -> pi(+) pi(-) pi(+) (gamma) decay, inclusive of final-state radiation, has been measured using similar to 17 million tagged K+ mesons collected with the KLOE detector at DA Phi NE, the Frascati phi-factory. The result is: BR(K+ -> pi(+) pi(-) pi(+) (gamma)) = 0.05565 +/- 0.00031(stat) +/- 0.00025(syst) a factor similar or equal to 5 more precise with respect to the previous result. This work completes the program of precision measurements of the dominant kaon branching ratios at KLOE.

Open access
• Artikel i tidskrift

Czerwinski, E.; Moskal, P.; Silarski, M.; Bass, S. D. et al.

### Determination of the eta '-Proton Scattering Length in Free Space

Ingår i Physical Review Letters, s. 062004-, 2014.

#### Abstract

Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton beam of the cooler synchrotron COSY, we determine the excitation function for the pp --> pp eta' reaction close to threshold. Combining these data with previous results, we extract the scattering length for the eta'-proton potential in free space to be Re(alpha(p eta)') = 0 +/- 0.43 fm and Im(alpha(p eta)') = 0.37(-0.16)(+0.40) fm.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Charge symmetry breaking in dd -> He-4 pi(0) with WASA-at-COSY

Ingår i Physics Letters B, s. 44-49, 2014.

#### Abstract

Charge symmetry breaking (CSB) observables are a suitable experimental tool to examine effects induced by quark masses on the nuclear level. Previous high precision data from TRIUMF and IUCF are currently used to develop a consistent description of CSB within the framework of chiral perturbation theory. In this work the experimental studies on the reaction dd -> He-4 pi(0) have been extended towards higher excess energies in order to provide information on the contribution of p-waves in the final state. For this, an exclusive measurement has been carried out at a beam momentum of p(d) = 1.2GeV/c using the WASA-at-COSY facility. The total cross section amounts to sigma(tot) =(118 +/- 18(stat) +/- 13(sys) +/- 8(ext)) p band first data on the differential cross section are consistent with s-wave pion production.

Open access
• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Cross section ratio and angular distributions of the reaction p + d -> He-3 + eta at 48.8MeV and 59.8MeV excess energy

Ingår i European Physical Journal A, s. 100-, 2014.

#### Abstract

We present new data for angular distributions and on the cross section ratio of the p+d -> He-3+eta reaction at excess energies of Q - 48.8MeV and Q - 59.8 MeV. The data have been obtained at the WASA-at-COSY experiment (Forschungszentrum Julich) using a proton beam and a deuterium pellet target. While the shape of obtained angular distributions show only a slow variation with the energy, the new results indicate a distinct and unexpected total cross section fluctuation between Q = 20MeV and Q = 60 MeV, which might indicate the variation of the production mechanism within this energy interval.

• Artikel i tidskrift

### Chiral dynamics and peripheral transverse densities

Ingår i Journal of High Energy Physics (JHEP), s. 092-, 2014.

#### Abstract

In the partonic (or light-front) description of relativistic systems the electromagnetic form factors are expressed in terms of frame-independent charge and magnetization densities in transverse space. This formulation allows one to identify the chiral components of nucleon structure as the peripheral densities at transverse distances b = O(M-pi(-1)) and compute them in a parametrically controlled manner. A dispersion relation connects the large-distance behavior of the transverse charge and magnetization densities to the spectral functions of the Dirac and Pauli form factors near the two-pion threshold at time-like t = 4M(pi)(2), which can be computed in relativistic chiral effective field theory. Using the leading-order approximation we (a) derive the asymptotic behavior (Yukawa tail) of the isovector transverse densities in the "chiral" region b = O(M-pi(-1)) and the "molecular" region b = O(M-N(2)/M-pi(3)); (b) perform the heavy-baryon expansion of the transverse densities; (c) explain the relative magnitude of the peripheral charge and magnetization densities in a simple mechanical picture; (d) include Delta isobar intermediate states and study the peripheral transverse densities in the large-N-c limit of QCD; (e) quantify the region of transverse distances where the chiral components of the densities are numerically dominant; (f) calculate the chiral divergences of the b(2)-weighted moments of the isovector transverse densities (charge and anomalous magnetic radii) in the limit M-pi -> 0 and determine their spatial support. Our approach provides a concise formulation of the spatial structure of the nucleon's chiral component and offers new insights into basic properties of the chiral expansion. It relates the information extracted from low-t elastic form factors to the generalized parton distributions probed in peripheral high-energy scattering processes.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of electromagnetic Dalitz decays J/psi -> Pe(+)e(-)

Ingår i Physical Review D, 2014.

#### Abstract

Based on a sample of (225.3 +/- 2.8) x 10(6) J/psi events collected with the BESIII detector, the electromagnetic Dalitz decays of J/psi -> Pe(+)e(-)(P = eta'/eta/pi(0)) are studied. By reconstructing the pseudoscalar mesons in various decay modes, the decays J/psi -> eta'e(+)e(-), J/psi -> eta e(+)e(-), and J/psi -> pi(0)e(+)e(-) are observed for the first time. The branching fractions are determined to be B(J/psi -> eta'e(+)e(-)) = (5.81 +/- 0.16 +/- 0.31) x 10(-5), B(J/psi -> eta e(+)e(-)) = (1.16 +/- 0.07 +/- 0.06) x 10(-5), and B(J/psi -> pi(0)e(+)e(-)) = (7.56 +/- 1.32 +/- 0.50) x 10(-7), where the first errors are statistical and the second ones systematic.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of e(+)e(-) -> p(p)over-bar in the vicinity of psi(3770)

Ingår i Physics Letters B, s. 101-107, 2014.

#### Abstract

Using 2917 pb(-1) of data accumulated at 3.773 GeV, 44.5 pb(-1) of data accumulated at 3.65 GeV and data accumulated during a psi(3770) line-shape scan with the BESIII detector, the reaction e(+)e(-) -> p (p) over bar is studied considering a possible interference between resonant and continuum amplitudes. The cross section of e(+)e(-) -> psi(3770) -> p (p) over bar, sigma(e(+)e(-)-> psi(3770) -> p (p) over bar), is found to have two solutions, determined to be (0.059(-0.020)(+0.070) +/- 0.012) pb with the phase angle phi = (255.8(-26.6)(+39.0) +/- 4.8). (< 0.166 pb at the 90% confidence level), or sigma(e(+)e(-) -> psi(3770) -> p<(p)over bar>) = (2.57(-0.13)(+0.12) +/- 0.12) pb with phi = (266.9(-6.3)(+6.1) +/- 0.9)degrees both of which agree with a destructive interference. Using the obtained cross section of psi(3770) -> p (p) over bar, the cross section of p (p) over bar -> psi(3770), which is useful information for the future PANDA experiment, is estimated to be either (9.8(-3.9)(+11.8)) nb (< 27.5 nb at 90% C.L.) or (425.6(-43.7)(+42.9)) nb. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Precision measurement of the mass of the tau lepton

Ingår i Physical Review D, 2014.

#### Abstract

An energy scan near the tau pair production threshold has been performed using the BESIII detector. About 24 pb(-1) of data, distributed over four scan points, were collected. This analysis is based on t pair decays to ee, e mu, eh, h, hh, e.,. and p. final states, where h denotes a charged p or K. The mass of the t lepton is measured from a maximum likelihood fit to the t pair production cross- section data to be m(tau) = 1776.91 +/- 0.12_0.10 - 0.13 _ MeV/c(2), which is currently the most precise value in a single measurement.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of eta' -> pi(+) pi(-) pi(+) pi(-) and eta' -> pi(+) pi(-) pi(0) pi(0)

Ingår i Physical Review Letters, s. 251801-, 2014.

#### Abstract

Using a sample of 1.3 x 10(9) J/psi events collected with the BESIII detector, we report the first observation of eta' -> pi(+) pi(-) pi(+) pi(-) and eta' -> pi(+) pi(-) pi(0) pi(0). The measured branching fractions are B(eta' -> pi(+) pi(-) pi(+) pi(-)) = [8.53 +/- 0.69(stat.) +/- 0.64(syst.)] x 10(-5) and B(eta' -> pi(+) pi(-) pi(0) pi(0)) = [1.82 +/- 0.35(stat.) +/- 0.18(syst.)] x 10(-4), which are consistent with theoretical predictions based on a combination of chiral perturbation theory and vector-meson dominance.

• Artikel i tidskrift

Ablikim, M.; Achasov, N.; Ai, X. C.; Albayrak, O. et al.

### Measurement of the branching fraction for psi(3686) -> omega K+K-

Ingår i Physical Review D, s. 112006-, 2014.

#### Abstract

With 1.06 x 10(8) psi(3686) events collected with the BESIII detector, the branching fraction of psi(3686) -> omega K+K- is measured to be (1.54 +/- 0.04 +/- 0.11) x 10(-4). This is the most precise result to date, due to the largest psi(3686) sample, improved signal reconstruction efficiency, good simulation of the detector performance, and a more accurate knowledge of the continuum contribution. Using the branching fraction of J/psi -> omega K+K-, the ratio B(psi(3868) -> K+K-)/B(J/psi -> K+K-) is determined to be (18.4 +/- 3.7)%. This constitutes a significantly improved test of the 12% rule, with the uncertainty now dominated by the J/psi branching fraction.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for the radiative transitions Psi(3770) -> gamma eta(c) and gamma eta(c) (2S)

Ingår i Physical Review D, s. 112005-, 2014.

#### Abstract

By using a 2.92 fb-1 data sample taken at pffisffiffi 3.773 GeV with the BESIII detector operating at the BEPCII collider, we search for the radiative transitions.d3770c and cd2S through the hadronic decays cdcd2S. K0 SK p. No significant excess of signal events above background is observed. We set upper limits at a 90% confidence level for the product branching fractions to be Bdd3770cxBd.c. K0 SK k p < 1.6x10-5 and Bd.d3770cd2SxBd.cd2S. K0 SK p<5.6x10-6. Combining our result with world-average values of Bd.cd.cd2S. K0 SK p, we find the branching fractions Bd.d3770c< 6.8 x 10-4 and Bd.d3770cd2S< 2.0 x 10-3 at a 90% confidence level.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of J/psi -> p(p)over-bara(0)(980) at BESIII

Ingår i Physical Review D, s. 052009-, 2014.

#### Abstract

Using 2.25 x 10(8) J/psi events collected with the BESIII detector at the BEPCII storage rings, we observe for the first time the process J/psi -> p (p) over bara(0)(980) -> pi(0)eta with a significance of 6.5 sigma (3.2 sigma including systematic uncertainties). The product branching fraction of J/psi -> p (p) over bara(0)(980) -> p (p) over bara(0)pi(0)eta is measured to be (6.8 +/- 1.2 +/- 1.3) x 10(-5), where the first error is statistical and the second is systematic. This measurement provides information on the a(0) production near threshold coupling to p (p) over bar and improves the understanding of the dynamics of J/psi decays to four-body processes.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Neutron-proton scattering in the context of the d*(2380) resonance

Ingår i Physical Review C. Nuclear Physics, s. 035204-, 2014.

#### Abstract

New data on quasifree polarized neutron-proton scattering in the region of the recently observed d* resonance structure are obtained by exclusive and kinematically complete high-statistics measurements with WASA at COSY. This paper details the determination of the beam polarization, checks of the quasifree character of the scattering process, on all obtained Ay angular distributions and on the new partial-wave analysis, which includes the new data producing a resonance pole in D-3(3)-(3)G(3) coupled partial waves at (2380 +/- 10 - i40 +/- 5) MeV-in accordance with the d* dibaryon resonance hypothesis. The effect of the new partial-wave solution on the description of total and differential cross-section data as well as specific combinations of spin-correlation and spin-transfer observables available from COSY-ANKE measurements at T-d = 2.27 GeV is discussed.

• Artikel i tidskrift

Makonyi, K.; von Wurtemberg, K. Marcks; Tegner, P. -E; Hansen, K. et al.

### Evaluating vacuum phototriodes designed for the PANDA electromagnetic calorimeter

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 36-43, 2014.

#### Abstract

In this work properties of a vacuum phototriode (VPT) and preamplifier unit designed for the electromagnetic calorimeter of the PANDA experiment being built at FAIR are investigated. With the use of lead tungstate and lanthanium bromide scintillators the VPT properties are studied at low photon energies, from tens of key in the lanthanium bromide measurements and between 10 MeV and 60 MeV in the lead tungstate measurements. At these energies the noise of the VPT unit can be expected to influence its performance significantly. It is shown that the noise contribution to the measured energy resolution, under optimal conditions, is consistent with a fluctuation of (one standard deviation) approximately 200 electrons at the VPT anode. For a lead tungstate crystal this is equivalent to a noise of 1.2 MeV. For lanthanium bromide this makes it possible to use VPTs for gamma ray spectroscopy above a few hundreds of keV without noticeable effects on the energy resolution compared to measurements with a standard photomultiplier. (C) 2014 Elsevier B.V. All rights reserved.

• Artikel i tidskrift

Babusci, D.; Balwierz-Pytko, I.; Bencivenni, G.; Bloise, C. et al.

### Search for light vector boson production in e(+)e(-) -> mu(+)mu(-)gamma interactions with the KLOE experiment

Ingår i Physics Letters B, s. 459-464, 2014.

#### Abstract

We have searched for a light vector boson U, the possible carrier of a "dark force", with the KLOE detector at the DA Phi NE e(+)e(-) collider, motivated by astrophysical evidence for the presence of dark matter in the Universe. Using e(+)e(-) collisions collected with an integrated luminosity of 239.3 pb(-1), we look for a dimuon mass peak in the reaction e(+)e(-) -> mu(+)mu(-)gamma, corresponding to the decay U -> mu(+)mu(-). We find no evidence for a U vector boson signal. We set a 90% CL upper limit for the mixing parameter squared between the photon and the U boson of 1.6 x 10(-5) to 8.6 x 10(-7) for the mass region 520 < m(U) < 980 MeV.

Open access
• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Study of e(+)e(-) -> p(p)over-bar pi(0) in the vicinity of the psi(3770)

Ingår i Physical Review D, s. 032007-, 2014.

#### Abstract

The process e(+)e(-) -> p (p) over bar pi(0) has been studied by analyzing data collected at root s = 3.773 GeV, root s = 3.650 GeV, and during a psi(3770) line shape scan with the BESIII detector at the BEPCII collider. The Born cross section of p (p) over bar pi(0) in the vicinity of the psi(3770) is measured, and the Born cross section of psi(3770) -> p (p) over bar pi(0) is extracted considering interference between resonant and continuum production amplitudes. Two solutions with the same probability and a significance of 1.5 sigma are found. The solutions for the Born cross section of psi(3770) -> p (p) over bar pi(0) are 33.8 +/- 1.8 +/- 2.1 pb and 0.06(-0.04-0.01)(+0.10+0.01) pb (< 0.22 pb at a 90% confidence level). Using the estimated cross section and a constant decay amplitude approximation, the cross section sigma(p<(p)over bar> -> psi(3770)pi(0)) is calculated for the kinematic situation of the planned (p) over bar ANDA experiment. The maximum cross section corresponding to the two solutions is expected to be less than 0.79 nb at 90% confidence level and 122 +/- 10 nb at a center-of-mass energy of 5.26 GeV.

• Artikel i tidskrift

Moradi, F. Ghazi; Qi, C.; Cederwall, B.; Atac, A. et al.

### Character of particle-hole excitations in Ru-94 deduced from gamma-ray angular correlation and linear polarization measurements

Ingår i Physical Review C. Nuclear Physics, s. 014301-, 2014.

#### Abstract

Linear polarization and angular correlations of gamma-rays depopulating excited states in the neutron-deficient nucleus Ru-94(44)50 have been measured, enabling firm spin-parity assignments for several excited states in this nucleus. The deduced multipolarities of strong transitions in the yrast structure were found to be mostly of stretched M1, E1, and E2 types and, in most cases, in agreement with previous tentative assignments. The deduced multipolarity of the 1869 keV and the connecting 257 and 1641 keV transitions indicates that the state at 6358 keV excitation energy has spin parity 12(1)(-) rather than 12(3)(+) as proposed in previous works. The presence of a 12(1)(-) state is interpreted within the framework of large-scale shell-model calculations as a pure proton-hole state dominated by the pi(p(1/2)(-1)circle times g(9/2)(-5)) and pi(p(3/2)(-1) g(9/2)(-5)) configurations. A new positive-parity state is observed at 6103 keV and is tentatively assigned as 12(2)(+). The 14(1)(-) state proposed earlier is reassigned as 13(4)(-) and is interpreted as being dominated by neutron particle-hole core excitations. The strengths of several E1 transitions have been measured and are found to provide a signature of core-excited configurations.

• Artikel i tidskrift

Senyigit, M.; Atac, A.; Akkoyun, S.; Kaskas, A. et al.

### Identification and rejection of scattered neutrons in AGATA

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 267-276, 2014.

#### Abstract

gamma Rays and neutrons, emitted following spontaneous fission of Cf-252, were measured in an AGATA experiment performed at INFN Laboratori Nazionali di Legnaro in Italy. The setup consisted of four AGATA triple cluster detectors (12 36 fold segmented high purity germanium crystals), placed at a distance of 50 cm from the source, and 16 HELENA BaF2 detectors. The aim of the experiment was to study the interaction of neutrons in the segmented high purity germanium detectors of AGATA and to investigate the possibility to discriminate neutrons and gamma rays with the gamma-ray tracking technique. The BaF2 detectors were used for a time measurement, which gave an independent discrimination of neutrons and gamma rays and which was used to optimise the gamma-ray tracking based neutron rejection methods. It was found that standard gamma-ray tracking, without any additional neutron rejection features, eliminates effectively most of the interaction points clue to recoiling Ge nuclei after elastic scattering of neutrons. Standard Cracking rejects also a significant amount of the events due to inelastic scattering of neutrons in the germanium crystals. Further enhancements of the neutron rejection was obtained by setting conditions on the following quantities, which were evaluated for each event by the Cracking algorithm: energy of the first and second interaction point, difference in the calculated incoming direction of the gamma ray, and figure-of-merit value. The experimental results of Cracking with neutron rejection agree rather well with GEANT4 simulations.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of e(+)e(-) -> gamma X(3872) at BESIII

Ingår i Physical Review Letters, s. 092001-, 2014.

#### Abstract

With data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.009 to 4.420 GeV, the process e(+)e(-) -> gamma X(3872) is observed for the first time with a statistical significance of 6.3 sigma. The measured mass of the X(3872) is (3871.9 +/- 0.7(stat) +/- 0.2(syst)) MeV/c(2), in agreement with previous measurements. Measurements of the product of the cross section sigma[e(+)e(-) -> gamma X(3872)] and the branching fraction B [X(3872) -> pi(+)pi(-)J/psi] at center-of-mass energies 4.009, 4.229, 4.260, and 4.360 GeV are reported. Our measurements are consistent with expectations for the radiative transition process Y(4260) -> gamma X(3872).

• Artikel i tidskrift

Louchart, C.; Obertelli, A.; Goergen, A.; Korten, W. et al.

### Collective nature of low-lying excitations in Zn-70,Zn-72,Zn-74 from lifetime measurements using the AGATA spectrometer demonstrator

Ingår i Physical Review C. Nuclear Physics, 2013.

#### Abstract

Background: Neutron-rich nuclei with protons in the fp shell show an onset of collectivity around N=40. Spectroscopic information is required to understand the underlying mechanism and to determine the relevant terms of the nucleon-nucleon interaction that are responsible for the evolution of the shell structure in this mass region. Methods: We report on the lifetime measurement of the first 2(+) and 4(+) states in Zn-70,Zn-72 ,Zn-74 and the first 6(+) state in Zn-72 using the recoil distance Doppler shift method. The experiment was carried out at the INFN Laboratory of Legnaro with the AGATA demonstrator, first phase of the Advanced Gamma Tracking Array of highly segmented, high-purity germanium detectors coupled to the PRISMA magnetic spectrometer. The excited states of the nuclei of interest were populated in the deep inelastic scattering of a Ge-76 beam impinging on a U-238 target. Results: The maximum of collectivity along the chain of Zn isotopes is observed for Zn-72 at N=42. An unexpectedly long lifetime of 20(-5.2)(+1.8) ps was measured for the 4(+) state in Zn-74. Conclusions: Our results lead to small values of the B(E2;4(1)(+) -> 21(+))/B(E2;2(1)(+->)0(1)(+)) ratio for Zn-72,Zn-74, suggesting a significant noncollective contribution to these excitations. These experimental results are not reproduced by state-of-the-art microscopic models and call for lifetime measurements beyond the first 2(+) state in heavy zinc and nickel isotopes.

• Artikel i tidskrift

Palacz, M; Nyberg, Johan

### Odd-parity 100 Sn Core Excitations

Ingår i Acta Physica Polonica B, s. 491-, 2013.

• Artikel i tidskrift

Sanchez Lorente, Alicia; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### High precision γ spectroscopy of ΛΛ-hypernuclei at the PANDA experiment

Ingår i Journal of Physics, Conference Series, 2013.

#### Abstract

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at FAIR at Darmstadt (Germany). Thanks to the use of stored antiproton beams, copious production of double ΛΛ-Hypernuclei is expected at the PANDA experiment, which will enable high precision gamma spectroscopy of such nuclei for the first time. At PANDA excited states of hypernuclei will be used as a starting point for the formation of double ΛΛ-Hypernuclei. In order to predict the yield of particle-stable double hypernuclei a microcanonical decay model was developed. For the detection of these nuclei, a devoted hypernuclear detector setup is planned. This set-up consists, in addition to the general purpose of the PANDA set-up, of a primary nuclear target for the production of pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform gamma spectroscopy. Moreover, one of the most challenging issues of this project is the fact that all detector systems need to operate in the presence of a high magnetic field and a large hadronic background. In these proceedings details concerning the identification procedure of double hypernuclei and the suppression of background will be presented. In addition, the current status of the activities related to the detector developments for this challenging programme will be briefly given.

• Artikel i tidskrift

Moeini, Hossein; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Design Studies of the PWO Forward End-cap Calorimeter for PANDA

Ingår i European Physical Journal A, s. 138-, 2013.

#### Abstract

The PANDA detection system at FAIR, Germany, is designed to study antiproton-proton annihilations, in order to investigate among others the realm of charm-meson states and glueballs, which has still much to reveal. The yet unknown properties of this field are to be unraveled through studying QCD phenomena in the non-perturbative regime. The multipurpose PANDA detector will be capable of tracking, calorimetry, and particle identification, and is foreseen to run at high luminosities providing average reaction rates up to 20 Million interactions/s. The envisaged physics program requires measurements of photons and charged particles with excellent energy, position, and time resolutions. The electromagnetic calorimeter (EMC) will serve as one of the basic components of the detector setup and comprises cooled Lead-Tungstate (PbWO4) crystals. This paper presents the mechanical design of the Forward End-cap calorimeter and analyses the response of this detector component in conjunction with the full EMC and the complete PANDA detector. The simulation studies are focused on the performance of the planned EMC with respect to the energy and spatial resolution of the reconstructed photons. Results of the Monte Carlo simulations, excluding very low-energy photons, have been validated by data obtained from a prototype calorimeter and shown to fulfil the requirements imposed by the PANDA physics program.

• Artikel i tidskrift

Calvo, Daniela; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The silicon Micro Vertex Detector of the PANDA\$ experiment

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 39-42, 2013.

#### Abstract

The PANDA experiment will make use of cooled antiproton beams of unprecedented quality that will become available at the Facility for Antiproton and Ion Research in Darmstadt, featuring a 1.5-15GeV/c momentum range. The physics program includes measurements of hyperons produced at low energies, spectroscopy of charmonium and open-charm mesons. To handle the forward peaked particle distribution due to the Lorentz boost, the apparatus is arranged in an asymmetric layout around the interaction point. In particular the Micro Vertex Detector based on silicon devices will have a rather unusual geometry. The MVD features fast data readout, since the experiment is triggerless, particle identification over the full range of energies, limited material budget and good spatial and time resolution. The status of the MVD design is shown and the present prototypes are described.

• Artikel i tidskrift

Kavatsyuk, Myroslav; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Trigger-less readout system with pulse pile-up recovery for the PANDA electromagnetic calorimeter

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 217-219, 2013.

#### Abstract

A simple, efficient, and robust on-line data-processing scheme was developed for the digital front-end electronics of the electromagnetic calorimeter of the PANDA spectrometer at FAIR, Darmstadt. The implementation of the processing algorithm in FPGA enables the construction of an almost dead-time free data acquisition system. The prototype of a complete trigger-less readout chain has been developed and evaluated. The precision of time synchronisation commands has been verified. A pile-up recovery algorithm was developed and evaluated over a large dynamic range of signal amplitudes.

• Artikel i tidskrift

Destefanis, Marco; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The PANDA experiment at FAIR

Ingår i Nuclear physics B, Proceedings supplements, s. 199-206, 2013.

#### Abstract

The PANDA (antiProton ANnihilation at DArmstadt) experiment is one of the major projects in preparation at the upcoming FAIR facility in Darmstadt, Germany. It will study interactions between antiprotons and protons or nuclei in the momentum range from 1.5 GeV/c to 15 GeV/c. The PANDA scientific program will address a wide range of topics, all aiming at improving our understanding of the strong interaction and hadron structure. The PANDA detector is a general-purpose spectrometer that will collect high quality and high statistics data in the fields of meson spectroscopy, baryon-antibaryon production, baryon spectroscopy, hypernuclear physics, hadron properties in the nuclear medium, and nucleon structure. This paper reviews some of the main physics topics of the experiment, together with a presentation of the detector.

• Artikel i tidskrift

Destefanis, Marco; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Drell-Yan studies in ppbar reactions at FAIR

Ingår i Physics of particles and nuclei, s. 886-889, 2013.

#### Abstract

The nucleonic structure is far to be completely understood. A transverse momentum dependent description of the nucleon structure is a crucial mile stone for several forthcoming studies in a wide range of experimental scenarios. By mean of antiproton beams, eventually polarized, that will be available at the future FAIR facility with a beam momentum up to 15 GeV/ c , the nonperturbative region of the QCD could be accessed. One of the main goal of the forthcoming expe riments at FAIR is the investigation of those Drell– Yan lepton pairs produced in protonantiproton annihila tions, taking advantage of the high expected lumi nosities. Drell–Yan studies are a unique tool to acce ss the spin depending properties of the nucleon, and namely its transverse degrees of freedom. Transver se Momentum Dependent (TMD) Parton Distribution Functions (PDFs), in particular the Boer–Mulders, the Sivers and the Transversity distribution functions, could be widely investigated by mean of the correspon ding experimental azimuthal asymmetries. In later stages of FAIR, single and doublespin asymmetries could be investigated as well. The Drell–Yan physics program which could be accessed at FAIR will be discussed in details, with a particular focus on the PANDA experimental scenario

• Artikel i tidskrift

Mochalov, Vasily; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Physics with antiprotons at PANDA

Ingår i Nuclear physics B, Proceedings supplements, s. 124-131, 2013.

#### Abstract

The PANDA collaboration (anti-Proton ANnihilations at DArmstadt) is a next generation hadron physics experiment to be operated at the future Facility for Antiproton and Ion Research (FAIR) at Darmstadt, Germany. It will use intensive cooled antiproton beams with a momentum between 1.5 GeV/c and 15 GeV/c. The PANDA detector is a state-of-the-art internal target detector allowing the detection and identification of neutral and charged particles almost in the whole solid angle.

• Artikel i tidskrift

Maggiora, Marco; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Proton time-like form factors at PANDA

Ingår i AIP Conference Proceedings, s. 588-590, 2013.

#### Abstract

A global description of the nucleonstructure in the complete kinematic region is needed. The ̄PANDA experimental scenario at FAIR could allow for an independent evaluation of the proton Time-Like Form Factors and for the investigation of an unprecedented large q2 range in order to probe their asymptotic behaviour. The sensitivity to higher order contributions to Born approximation is discussed as well.

• Artikel i tidskrift

Zotti, Laura; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The Micro-Vertex-Detector for the bar PANDA experiment

Ingår i Journal of Physics, Conference Series, 2013.

#### Abstract

PANDA is a fixed target experiment that will be carried out at the future FAIR facility. PANDA will provide an excellent tool to address fundamental question in the field of hadronic physics, with a physic program that extends from the investigation of QCD (providing insight in the mechanisms of mass generation and confinement) to the test of fundamental symmetries. The Micro-Vertex-Detector located in the innermost part of the central tracking system will be composed by hybrid pixel and double-sided micro-strip silicon detectors. The Micro-Vertex-Detector will play an important role for the PANDA physics goals. The possibility to reconstruct the secondary vertices and the applicability of a precise D meson tagging is essential for the spectroscopy in the open charm sector and the charmonium mass region. To this aim the Micro-Vertex-Detector features a spatial resolution better than 100μm, a time resolution better than 20ns, a limited material budget, and a high data rate capability in a triggerless environment. An overview of the Micro-Vertex-Detector related to the physics goals will be presented.

• Konferensbidrag

Marciniewski, Pawel; Fransson, Kjell; Heijkenskjöld, Lena; Kupsc, Andrzej et al.

### A Trigger System based on fast sampling ADCs - implementations and tests

2013.

• Artikel i tidskrift

Terschlüsen, Carla; Leupold, Stefan; Lutz, M.F.M.

### Dynamics of the low-lying pseudoscalar and vector mesons

Ingår i PoS Bormio2013, s. 046-, 2013.

• Konferensbidrag

Michler, Frank; van Hees, Hendrik; Dietrich, Dennis D.; Leupold, Stefan et al.

### Non-equilibrium photon production arising from the chiral mass shift

s. 055- 2013.

• Artikel i tidskrift

Adlarson, Patrik; Calén, Hans; Fransson, Kjell; Gullström, Carl-Oscar et al.

### Search for a dark photon in the π0 →e+e- decay

Ingår i Physics Letters B, s. 187-193, 2013.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Search for eta(c)(2S)h(c) -> p(p)over-bar decays and measurements of the chi(cJ) -> p(p)over-bar branching fractions

Ingår i Physical Review D, s. 112001-, 2013.

#### Abstract

Using a sample of 1.06 x 10(8)psi(3686) events collected with the BESIII detector at BEPCII, the decays eta(c)(2S) -> p (p) over bar and h(c) -> p (p) over bar are searched for, where eta(c)(2S) and h(c) are reconstructed in the decay chains psi(3686) -> gamma eta(c)(2S), eta(c)(2S) -> p (p) over bar and psi(3686) -> pi(0)h(c), h(c) -> p (p) over bar, respectively. No significant signals are observed. The upper limits of the product branching fractions are determined to be B(psi(3686) -> gamma eta(c)(2S)) x B(eta(c)(2S) -> p (p) over bar) < 1.4 x 10(-6) and B(psi(3686) -> pi(0)h(c)) x B(h(c) -> p<(p)over bar>) < 1.3 x 10(-7) at the 90% C.L.. The branching fractions for chi(cJ) -> p<(p)over bar> (J = 0, 1, 2) are also measured to be (24.5 +/- 0.8 +/- 1.3, 8.6 +/- 0.5 +/- 0.5, 8.4 +/- 0.5 +/- 0.5) x 10(-5), which are the world's most precise measurements.

• Artikel i tidskrift

Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O. et al.

### Observation of the decay psi(3686) -> Lambda(Sigma)over-bar(+/-) pi(-/+) + c.c

Ingår i Physical Review D, s. 112007-, 2013.

#### Abstract

Using a sample of 1:06 X 10(8) psi(3686) events collected with the BESIII detector, we present the first observation of the decays of psi(3686) -> Lambda(Sigma) over bar (+) pi(-) + c.c. and psi(3686) -> Lambda(Sigma) over bar (-) pi(+) + c.c. The branching fractions are measured to be B(psi(3686) -> Lambda(Sigma) over bar (+) pi(-) + c.c.) = (1.40 +/- 0.03 +/- 0.13) X 10(-4) and B(psi(3686) -> Lambda (Sigma) over bar (-) pi(+) + c.c.) = (1.54 +/- 0.04 +/- 0.13) X 10(-4) where the first errors are statistical and the second ones systematic.

• Artikel i tidskrift

Hanhart, C.; Kupsc, Andrzej; Meissner, U-G; Stollenwerk, F. et al.

### Dispersive analysis for eta ->gamma gamma*

Ingår i European Physical Journal C, s. 2668-, 2013.

#### Abstract

A dispersion integral is derived that connects data on eta ->pi (+) pi (-) gamma to the eta ->gamma gamma (au) transition form factor. A detailed analysis of the uncertainties is provided. We find for the slope of the eta transition form factor at the origin . Using an additional, plausible assumption, one finds for the corresponding slope of the eta' transition form factor, . Both values are consistent with all recent data, but differ from some previous theoretical analyses.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Measurement of the pn -> pp pi(0)pi(-) reaction in search for the recently observed resonance structure in d pi(0)pi(0) and d pi(+)pi(-) systems

Ingår i Physical Review C. Nuclear Physics, s. 055208-, 2013.

#### Abstract

Exclusive measurements of the quasifree pn -> pp pi(0)pi(-) reaction have been performed by means of pd collisions at T-p = 1.2 GeV using the wide angle shower apparatus (WASA) detector setup at the cooler synchrotron COSY (Institut fur Kernphysik, Julich). Total and differential cross sections have been obtained covering the energy region root s = (2.35-2.46) GeV, which includes the region of the ABC effect and its associated resonance structure. NoABCeffect, i.e., low-mass enhancement is found in the pi(0)pi(-) -invariant mass spectrum, in agreement with the constraint from Bose statistics that the isovector pion pair can not be in relative s wave. At the upper end of the covered energy region t-channel processes for Roper, Delta(1600) and Delta Delta excitations provide a reasonable description of the data, but at low energies the measured cross sections are much larger than predicted by such processes. Adding a resonance amplitude for the resonance at m = 2.37 GeV with Gamma = 70 MeV and I (J(P)) = 0(3(+)) observed recently in pn -> d pi(0)pi(0) and pn -> d pi(+)pi(-) reactions leads to an agreement with the data also at low energies.

• Artikel i tidskrift

Michler, Frank; van Hees, Hendrik; Dietrich, Dennis D.; Leupold, Stefan et al.

### Off-equilibrium photon production during the chiral phase transition

Ingår i Annals of Physics, s. 331-393, 2013.

#### Abstract

In the early stage of ultrarelativistic heavy-ion collisions chiral symmetry is restored temporarily. During this so-called chiral phase transition, the quark masses change from their constituent to their bare values. This mass shift leads to the spontaneous non-perturbative creation of quark-antiquark pairs, which effectively contributes to the formation of the quark-gluon plasma. We investigate the photon production induced by this creation process. We provide an approach that eliminates possible unphysical contributions from the vacuum polarization and renders the resulting photon spectra integrable in the ultraviolet domain. The off-equilibrium photon numbers are of quadratic order in the perturbative coupling constants while a thermal production is only of quartic order. Quantitatively, we find, however, that for the most physical mass-shift scenarios and for photon momenta larger than 1 GeV the off-equilibrium processes contribute less photons than the thermal processes.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Investigation of the dd -> (3)Hen pi(0) reaction with the FZ Julich WASA-at-COSY facility

Ingår i Physical Review C. Nuclear Physics, s. 014004-, 2013.

#### Abstract

An exclusive measurement of the dd -> (3)Hen pi(0) reaction was carried out at a beam momentum of p(d) = 1.2 GeV/c using the WASA-at-COSY facility. Information on the total cross section as well as differential distributions was obtained. The data are described by a phenomenological approach based on a combination of a quasifree model and a partial wave expansion for the three-body reaction. The total cross section is found to be sigma(tot) = ( 2.89 +/- 0.01(stat) +/- 0.06(sys) +/- 0.29(norm)) mu b. The contribution of the quasifree processes ( with the beam or target neutron being a spectator) accounts for 38% of the total cross section and dominates the differential distributions in specific regions of phase space. The remaining part of the cross section can be described by a partial wave decomposition indicating the significance of p-wave contributions in the final state.

• Artikel i tidskrift

Branchini, P.; Budano, A.; Balla, A.; Beretta, M. et al.

### Front-end DAQ strategy and implementation for the KLOE-2 experiment

Ingår i Journal of Instrumentation, s. T04004-, 2013.

#### Abstract

A new front-end data acquisition (DAQ) system has been conceived for the data collection of the new detectors which will be installed by the KLOE2 collaboration. This system consists of a general purpose FPGA based DAQ module and a VME board hosting up to 16 optical links. The DAQ module has been built around a Virtex-4 FPGA and it is able to acquire up to 1024 different channels distributed over 16 front-end slave cards. Each module is a general interface board (GIB) which performs also first level data concentration tasks. The GIB has an optical interface, a RS-232, an USB and a Gigabit Ethernet Interface. The optical interface will be used for DAQ purposes while the Gigabit Ethernet interface for monitoring tasks and debug. Two new detectors exploit this strategy to collect data. Optical links are used to deliver data to the VME board which performs data concentration tasks. The return optical link from the board to the GIB is used to initialize the front-end cards. The VME interface of the module implements the VME 2eSST protocol in order to sustain a peak data rate of up to 320 MB/s. At the moment the system is working at the Frascati National Laboratory (LNF).

• Artikel i tidskrift

Babusci, D.; Badoni, D.; Balwierz-Pytko, I.; Bencivenni, G. et al.

### A new limit on the CP violating decay K-S -> 3 pi(0) with the KLOE experiment

Ingår i Physics Letters B, s. 54-60, 2013.

#### Abstract

We have carried out a new direct search for the CP violating decay K-S -> 3 pi(0) with 1.7 fb(-1) of e(+)e(-) collisions collected by the KLOE detector at the Phi-factory DA Phi NE. We have searched for this decay in a sample of about 5.9 x 10(8) KSKL events tagging the K-S by means of the K-L interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake K-S tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of K-S -> 2 pi(0) events in the same sample, we set the upper limit on BR(K-S -> 3 pi(0)) <= 2.6 x 10(-8) at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta(000) parameter, vertical bar eta(000)vertical bar <= 0.0088 at 90% C.L., improving by a factor two the latest direct measurement. (c) 2013 Elsevier B.V. All rights reserved.

• Artikel i tidskrift

Babusci, D.; Badoni, D.; Balwierz-Pytko, I.; Bencivenni, G. et al.

### Precision measurement of sigma (e(+)e(-) -> pi(+)pi(-)gamma)/sigma(e(+)e(-) ->mu(+)mu(-)gamma) and determination of the pi(+)pi(-) contribution to the muon anomaly with the KLOE detector

Ingår i Physics Letters B, s. 336-343, 2013.

#### Abstract

We have measured the ratio cr (e(+)e(-) -> pi(+)pi(-)gamma)/sigma(e(+)e(-) -> mu(+)mu(-)gamma), with the KLOE detector at DA Phi NE for a total integrated luminosity of similar to 240 pb(-1). From this ratio we obtain the cross section sigma (e(+)e(-) -> pi(+)pi(-)gamma). From the cross section we determine the pion form factor vertical bar F-pi vertical bar(2) and the two-pion contribution to the muon anomaly a(mu) for 0.592< M-pi pi < 0.975 GeV, Delta(pi pi) a(mu) = (385.1 +/- 1.1(stat) +/- 2.7(sys+theo)) x 10(-10). This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly. (c) 2013 Elsevier B.V. All rights reserved.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Search for eta-mesic He-4 with the WASA-at-COSY detector

Ingår i Physical Review C. Nuclear Physics, s. 035204-, 2013.

#### Abstract

An exclusive measurement of the excitation function for the dd -> (3)Hep pi(-) reaction was performed at the Cooler Synchrotron COSY-Julich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 to 2.400 GeV/c crossing the kinematic threshold for the eta-meson production in the dd -> He-4 eta reaction at 2.336 GeV/c. The corresponding excess energy with respect to the He-4-eta system varied from -51.4 to 22 MeV. The integrated luminosity in the experiment was determined using the dd -> (3)Hen reaction. The shape of the excitation function for the dd -> (3)Hep pi(-) reaction was examined. No signal of the He-4-eta bound state was observed. An upper limit for the cross section for the bound state formation and decay in the process dd -> (He-4-eta)(bound) -> (3)Hep pi(-) was determined on the 90% confidence level and it varies from 20 to 27 nb for the bound state width ranging from 5 to 35 MeV, respectively.

• Artikel i tidskrift

Babusci, D.; Badoni, D.; Balwierz-Pytko, I.; Bencivenni, G. et al.

### Limit on the production of a light vector gauge boson in phi meson decays with the KLOE detector

Ingår i Physics Letters B, s. 111-115, 2013.

#### Abstract

We present a new limit on the production of a light dark-force mediator with the KLOE detector at DA Phi NE. This boson, called U, has been searched for in the decay phi -> eta U, U -> e(+)e(-), analyzing the. decay eta -> pi(0)pi(0)pi(0) in a data sample of 1.7 fb(-1). No structures are observed in the e(+)e(-) invariant mass distribution over the background. This search is combined with a previous result obtained from the decay eta -> pi(+)pi(-)pi(0), increasing the sensitivity. We set an upper limit at 90% C.L. on the ratio between the U boson coupling constant and the fine structure constant of alpha'/alpha < 1.7 x 10(-5) for 30 < M-U < 400 MeV and alpha'/alpha <= 8 x 10(-6) for the sub-region 50 < M-U <210 MeV. This result assumes the Vector Meson Dominance expectations for the phi eta gamma* transition form factor. The dependence of this limit on the transition form factor has also been studied.

• Artikel i tidskrift

Erni, W.; Keshelashvili, I.; Krusche, B.; Steinacher, M. et al.

### Technical design report for the PANDA (AntiProton Annihilations at Darmstadt) Straw Tube Tracker

Ingår i European Physical Journal A, s. 25-, 2013.

#### Abstract

This document describes the technical layout and the expected performance of the Straw Tube Tracker (STT), the main tracking detector of the PANDA target spectrometer. The STT encloses a Micro-Vertex-Detector (MVD) for the inner tracking and is followed in beam direction by a set of GEM stations. The tasks of the STT are the measurement of the particle momentum from the reconstructed trajectory and the measurement of the specific energy loss for a particle identification. Dedicated simulations with full analysis studies of certain proton-antiproton reactions, identified as being benchmark tests for the whole PANDA scientific program, have been performed to test the STT layout and performance. The results are presented, and the time lines to construct the STT are described.

• Artikel i tidskrift

Babusci, D.; Badoni, D.; Balwierz-Pytko, I.; Bencivenni, G. et al.

### Measurement of eta meson production in gamma gamma interactions and Gamma(eta -> gamma gamma) with the KLOE detector

Ingår i Journal of High Energy Physics (JHEP), s. 119-, 2013.

#### Abstract

We present a measurement of eta meson production in photon-photon interactions produced by electron-positron beams colliding with root s = 1 GeV. The measurement is done with the KLOE detector at the phi-factory DA Phi NE with an integrated luminosity of 0.24 fb(-1). The e(+)e(-) -> e(+)e(-)eta cross section is measured without detecting the outgoing electron and positron, selecting the decays eta -> pi(+)pi(-)pi(0) and eta -> pi(0)pi(0)pi(0). The most relevant background is due to e(+)e(-) -> eta gamma when the monochromatic photon escapes detection. The cross section for this process is measured as sigma(e(+)e(-) -> eta gamma) = (856 +/- 8(stat) +/- 16(syst)) pb. The combined result for the e(+)e(-) -> e(+)e(-)eta cross section is sigma(e(+)e(-) -> e(+)e(-)eta) = (32.72 +/- 1.27(stat) +/- 0.70(syst)) pb. From this we derive the partial width Gamma(eta -> gamma gamma) = (520 +/- 20(stat) +/- 13(syst)) eV. This is in agreement with the world average and is the most precise measurement to date.

• Artikel i tidskrift

Babusci, D.; Badoni, D.; Balwierz-Pytko, I.; Bencivenni, G. et al.

### Measurement of Γ(η→π+π-γ)/Γ(η→π+π-π0) with the KLOE detector

Ingår i Physics Letters B, s. 910-914, 2013.

#### Abstract

The ratio Rη=Γ(η→π+π-γ)/Γ(η→π+π-π0) has been measured by analysing 22 million φ→ηγ decays collected by the KLOE experiment at DAΦNE, corresponding to an integrated luminosity of 558 pb-1. The η→π+π-γ proceeds both via the ρ resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, Rη=0.1856±0.0005stat±0.0028syst, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the η→π+π-γ decay could be described in a model-independent approach in terms of a single free parameter, α. The determined value of the parameter α is α=(1.32±0.08stat-0.09syst+0.10±0.02theo) GeV-2.

• Artikel i tidskrift

Danilkin, I. V.; Lutz, M. F. M.; Leupold, Stefan; Terschlusen, Carla

### Photon-fusion reactions from the chiral Lagrangian with dynamical light vector mesons

Ingår i European Physical Journal C, s. 2358-, 2013.

#### Abstract

We study the reactions gamma gamma -> pi(0)pi(0), pi(+)pi(-), K-0(K) over bar (0), K+K-, eta eta and pi(0)eta based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains five unknown parameters that are relevant for the photon-fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon-fusion data gamma gamma -> pi(0)pi(0), pi(+)pi(-), pi(0)eta and to the decay eta -> pi(0)gamma gamma In order to derive gauge invariant reaction amplitudes in the resonance region constraints from maximal analyticity and exact coupled-channel unitarity are used. Our results are in good agreement with the existing experimental data from threshold up to about 0.9 GeV for the two-pion final states. The a(0) meson in the pi(0)eta channel is dynamically generated and an accurate reproduction of the gamma gamma -> pi(0)eta data is achieved up to 1.2 GeV. Based on our parameter sets we predict the gamma gamma -> K-0(K) over bar (0), K+K-, eta eta cross sections.

• Artikel i tidskrift

Nahrgang, Marlene; Herold, Christoph; Leupold, Stefan; Mishustin, Igor et al.

### The impact of dissipation and noise on fluctuations in chiral fluid dynamics

Ingår i Journal of Physics G, s. 055108-, 2013.

#### Abstract

We investigate the nonequilibrium evolution of the sigma field coupled to a fluid dynamic expansion of a hot fireball to model the chiral phase transition in heavy-ion collisions. The dissipative processes and fluctuations are allowed under the assumption that the total energy of the coupled system is conserved. We use the linear sigma model with constituent quarks to investigate the effects of the chiral phase transition on the equilibration and excitation of the sigma modes. The quark fluid acts as a heat bath in local thermal equilibrium and the sigma field evolves according to a semiclassical stochastic Langevin equation of motion. The effects of supercooling and reheating of the fluid in a first order phase transition are observed via the delayed relaxation of the sigma field to a new equilibrium state. At the first order phase transition the nonequilibrium fluctuations are strongly enhanced.

• Artikel i tidskrift

Hadynska-Klek, K.; Napiorkowski, P. J.; Maj, A.; Azaiez, F. et al.

### Towards The Determination Of Superdeformation In Ca-42

Ingår i Acta Physica Polonica B, s. 617-625, 2013.

#### Abstract

The Coulomb excitation experiment to study electromagnetic structure of low-lying states in Ca-42 with a focus on a possible superdeformation in this nucleus was performed at the Laboratori Nazionali di Legnaro in Italy. Preliminary values of the determined quadrupole deformation parameters for both the ground state band and the presumed superdeformed band are presented.

• Artikel i tidskrift

Palacz, M.; Nyberg, Johan; Grawe, H.; Sieja, K. et al.

### Odd-Parity Sn-100 Core Excitations

Ingår i Acta Physica Polonica B, s. 491-500, 2013.

#### Abstract

Odd-parity core excited states have been identified in two close neighbors of Sn-100: Pd-96 and Ag-97. This was done in an fusion-evaporation experiment, using a Ni-58 beam on a Sc-45 target. Even-parity core excited states in these nuclei are very well reproduced in large scale (LSSM) calculations in which particle-hole excitations are allowed with up to five g(9/2) protons and neutrons across the N = Z = 50 gap, to the g(7/2), d(5/2), d(3/2), and s(1/2) orbitals. The odd-parity states can only be qualitatively interpreted though, employing calculations in the full fpg shell model space, but with just one particle-hole core excitation allowed. A more complete model including odd-parity orbitals is need for the description of core excited states in the region of Sn-100.

• Artikel i tidskrift

Adlarson, P.; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Isospin decomposition of the basic double-pionic fusion in the region of the ABC effect

Ingår i Physics Letters B, s. 229-236, 2013.

#### Abstract

Exclusive and kinematically complete high-statistics measurements of the basic double-pionic fusion reactions pn -> d pi(0)pi(0), pn -> d pi(+)pi(-) and pp -> d pi(+)pi(0) have been carried out simultaneously over the energy region of the ABC effect using the WASA detector setup at COSY. Whereas the isoscalar reaction part given by the d pi(0)pi(0) channel exhibits the ABC effect, i.e. a low-mass enhancement in the pi pi-invariant mass distribution, as well as the associated resonance structure in the total cross section, the isovector part given by the d pi(+)pi(0) channel shows a smooth behavior consistent with the conventional t-channel Delta Delta process. The d pi(+)pi(-) data are very well reproduced by combining the data for isovector and isoscalar contributions, if the kinematical consequences of the isospin violation due to different masses for charged and neutral pions are taken into account.

• Artikel i tidskrift

Guastalla, G.; DiJulio, D. D.; Gorska, M.; Cederkall, J. et al.

### Coulomb Excitation of Sn-104 and the Strength of the Sn-100 Shell Closure

Ingår i Physical Review Letters, s. 172501-, 2013.

#### Abstract

A measurement of the reduced transition probability for the excitation of the ground state to the first 2(+) state in Sn-104 has been performed using relativistic Coulomb excitation at GSI. Sn-104 is the lightest isotope in the Sn chain for which this quantity has been measured. The result is a key point in the discussion of the evolution of nuclear structure in the proximity of the doubly magic nucleus Sn-100. The value B(E2; 0(+) -> 2(+)) = 0.10(4) e(2)b(2) is significantly lower than earlier results for Sn-106 and heavier isotopes. The result is well reproduced by shell model predictions and therefore indicates a robust N = Z = 50 shell closure.

Open access
• Artikel i tidskrift

Zheng, Y.; de France, G.; Clement, E.; Dijon, A. et al.

### gamma-ray linear polarization measurements and (g(9/2))(-3) neutron alignment in Ru-91

Ingår i Physical Review C. Nuclear Physics, s. 044328-, 2013.

#### Abstract

Linear polarization measurements have been performed for gamma rays in Ru-91 produced with the Ni-58(Ar-36,2p1n gamma)Ru-91 reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the gamma-gamma coincidences, gamma-ray linear polarization, and gamma-ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3-1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in Ru-91. More specifically, calculations using a semiempirical shell model were performed to understand the structures of the first and second (21/2(+)) and (17/2(+)) levels. The results are in good agreement with the experimental data, supporting the interpretation of the nonyrast (21/2(+)) and (17/2(+)) states in terms of the J(max) and J(max) - 2 members of the seniority-three nu(g(9/2))(-3) multiplet. DOI: 10.1103/PhysRevC.87.044328

• Artikel i tidskrift

Terschlüsen, Carla; Strandberg, Bruno; Leupold, Stefan; Eichstadt, Fabian

### Reactions with pions and vector mesons in the sector of odd intrinsic parity

Ingår i European Physical Journal A, s. 116-, 2013.

#### Abstract

TheWess-Zumino-Witten structure is supplemented by a simple vector-meson Lagrangian where the vector mesons are described by antisymmetric tensor fields. With the rho-omega-pi coupling as the only parameter in the sector of odd intrinsic parity, i.e. without additional contact terms, one can achieve a proper description of the decay of an omega-meson into three pions, the single-and double-virtual pion transition form factor and the three-pion production in electron-positron collisions.

• Artikel i tidskrift

Javier Egea, Francisco; Sanchis, Enrique; Gonzalez, Vicente; Gadea, Andres et al.

### Design and Test of a High-Speed Flash ADC Mezzanine Card for High-Resolution and Timing Performance in Nuclear Structure Experiments

Ingår i IEEE Transactions on Nuclear Science, s. 3526-3531, 2013.

#### Abstract

This work describes new electronics for the EX-OGAM2 (HP-Ge detector array) and NEDA (BC501A-based neutron detector array). A new digitizing card with high resolution has been designed for gamma-ray and neutron spectroscopy experiments. The higher bandwidth requirement of the NEDA signals, together with the necessity for accuracy, require a high sampling rate in order to preserve the shape for real-time Pulse Shape Analysis (PSA). The PSA is of paramount importance for the NEDA to discriminate between neutrons and gamma-ray signals. Both high resolution and high speed parameters are often difficult to achieve in a single electronic unit. These constraints, together with the need to build new digitizing electronics to improve performance and flexibility of signal analysis in nuclear physics experiments, led to the development a new FADC mezzanine card. In this work, the design and development are described, including the characterization procedure and the preliminary measurement results.

• Artikel i tidskrift

Vandone, V; Leoni, S; Assanelli, D; Bottoni, S et al.

### Study of the Order-to-Chaos transition in 174 W with the AGATA-Demonstrator

Ingår i Journal of Physics: Conference Series, 2012.

#### Abstract

The transition between order and chaos is studied in the warm rotating nucleus 174 W by Î³-spectroscopy, focusing on the conservation of selection rules of the K quantum number with the excitation energy, where K is the projection of the total angular momentum on the symmetry axis. The 174 W nucleus was populated by the fusion-evaporation reaction of 80 Ti (at 217 MeV) on a 128 Te backed target. The measurement was performed in July 2010 at Legnaro National Laboratories of INFN using the AGATA Demonstrator HPGe-array coupled to an array of 27 BaF 2 scintillators, named Helena. The data analysis concentrates on Î³-Î³ coincidence matrices selecting the Î³-decay flow populating low- K and high- K structures. By a statistical fluctuation analysis the total number of low- K and high- K bands can be evaluated as a function of excitation energy. Comparisons with cranked shell model calculations at finite temperature are used to extract information on the onset of the chaotic regime as a function of excitation energy.

• Artikel i tidskrift

Wadsworth, R; Singh, B S Nara; Liu, Z; Grawe, H et al.

### Spin-gap isomer in 96 Cd

Ingår i Journal of Physics: Conference Series, 2012.

#### Abstract

Evidence has been obtained for the existence of the long predicted 16 + spin-gap isomer in 96 Cd. The decay of the isomer was identified and studied following the use of an 850 MeV/u beam of 124 Xe impinging on a Be target and the fragment recoil separator at the GSI Laboratory. Gamma decays from the fragments were detected using the RISING gamma ray array, in its stopped beam configuration, plus a silicon active stopper. The data obtained have been compared with shell model predictions, which indicate that the isoscalar neutron-proton interaction plays a key role in the formation of the isomer.

• Artikel i tidskrift

Sanchez Lorente, Alicia; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### Double Λ-hypernuclei at the PANDA experiment

Ingår i Hyperfine Interactions, s. 41-50, 2012.

#### Abstract

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at FAIR at Darmstadt (Germany). Thanks to the use of stored antiproton beams, copious production of double ΛΛ-Hypernuclei is expected at the PANDA experiment, which will enable high precision gamma spectroscopy of such nuclei for the first time. At PANDA excited states of hypernuclei will be used as a starting point for the formation of double ΛΛ-Hypernuclei. In order to predict the yield of particle-stable double hypernuclei a microcanonical decay model was developed. For the detection of these nuclei, a devoted hypernuclear detector setup is planned. This set-up consists, in addition to the general purpose of the PANDA set-up, of a primary nuclear target for the production of pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform gamma spectroscopy. Moreover, one of the most challenging issues of this project is the fact that all detector systems need to operate in the presence of a high magnetic field and a large hadronic background. In these proceedings details concerning the identification procedure of double hypernuclei and the suppression of background will be presented. In addition, the current status of the activities related to the detector developments for this challenging programme will be briefly given.

• Konferensbidrag

Fioravanti, Elisa; Caldeira Balkeståhl, Li; Calen, Hans; Fransson, Kjell et al.

Ingår i The physics of excited nucleons, s. 391-394, 2012.

#### Abstract

FAIR a new International Facility for Antiproton and Ion Reaserach, is under construction at Darmstadt, in Germany. This will provide scientists in the world with outstanding beams and experimental conditions for studying matter at the level of atoms, nuclei, and other subnuclear constituents. An antiproton beam with intensity up to 2Oe107 p/s and high momentum resolution will be available at the High Energy Storage Ring (HESR) where the PANDA (Antiproton Annihilation At Darmstadt) detector will be installed. In this paper, we will illustrate the details of PANDA scientific program related to hadron spectroscopy, after a brief introduction about the FAIR facility and the PANDA detector.

• Artikel i tidskrift

De Santis, A.; Caldeira Balkeståh, Li; Höistad, Bo; Johansson, Tord et al.

### Recent results on CP and CPT tests at KLOE

Ingår i PoS, 2012.

• Konferensbidrag

Wuerschig, Thomas; Caldeira Balkeståhl, Li; Calen, Hans; Fransson, Kjell et al.

### Charm spectroscopy at the PANDA experiment

Ingår i Particles and nuclei, s. 329-331, 2012.

#### Abstract

Based on a short review of the current experimental status, future perspectives for the spectroscopy of charmed hadrons at P̄ANDA will be discussed. The main emphasis is on the sector of D mesons and charmonium systems. In contrast to other experiments, P̄ANDA will render possible high-precision spectroscopy for bound states of any quantum number. The expected detector performance is highlighted by simulation results of selected physics benchmark channels.

• Artikel i tidskrift

Nahrgang, M.; Leupold, Stefan; Bleicher, M.

### Nonequilibrium effects in dynamic symmetry breaking

Ingår i Acta Physica Polonica B, Proceedings Supplement, s. 1191-1196, 2012.

#### Abstract

We study the evolution of the sigma field fluctuations in a scenario featuring a critical point and a first order phase transition using the model of nonequilibrium chiral fluid dynamics (NχFD).

• Konferensbidrag

Johansson, Tord

### PANDA at fair

Ingår i International meeting Excited QC, s. 1197-1202, 2012.

#### Abstract

The PANDA experiment is one of the major projects at the upcoming FAIR facility in Darmstadt, Germany. It will study interactions between antiprotons and protons or nuclei in the momentum range of 1.5 GeV/c to 15 GeV/c with a 4π state-of-the-art detector. The purpose is to learn about fundamental aspects of the strong interaction in the transition region between perturbative QCD and nuclear phenomena. This paper reviews some of the main physics topics together with a presentation of the detector.

• Artikel i tidskrift

Guliyev, Elmaddin; Kavatsyuk, M.O.; Lemmens, P.J.J.; Tambave, G.J. et al.

### VHDL implementation of feature-extraction algorithm for the PANDA electromagnetic calorimeter

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 22-28, 2012.

#### Abstract

A simple, efficient, and robust feature-extraction algorithm, developed for the digital front-end electronics of the electromagnetic calorimeter of the PANDA spectrometer at FAIR, Darmstadt, is implemented in VHDL for a commercial 16 bit 100 MHz sampling ADC. The source-code is available as an open-source project and is adaptable for other projects and sampling ADCs. Best performance with different types of signal sources can be achieved through flexible parameter selection. The on-line data-processing in FPGA enables to construct an almost dead-time free data acquisition system which is successfully evaluated as a first step towards building a complete trigger-less readout chain. Prototype setups are studied to determine the dead-time of the implemented algorithm, the rate of false triggering, timing performance, and event correlations.

• Artikel i tidskrift

Bersani, Andrea; Caldeira Balkeståhl, Li; Calén, Hans; Fransson, Kjell et al.

### The PANDA detector at FAIR

Ingår i Physica scripta. T, s. 014006-, 2012.

#### Abstract

The PANDA detector will be installed at FAIR to enterprise a long-term, wide-spectrum physics program in the strong interaction framework. The detector will be installed at the HESR accumulation ring, which will provide an anti-proton beam of unprecedented luminosity and momentum definition. The beam will interact with an internal target. The detector has been designed to allow a 4π coverage around the interaction region. Due to the relatively high energy of the beam, up to 15 GeV, PANDA will feature two magnetic spectrometers: the target spectrometer (TS), with a superconducting solenoid and covering the interaction region, and a forward spectrometer (FS), with a normal-conducting dipole and covering the small angles region. Since the physics program is wide and the requirements on the various subsystems are different, the detector has been designed to be as flexible as possible. The complete detector will be described in detail, both from the viewpoint of the proposed techniques and from the viewpoint of the expected performances. An overview of the status of various components of the detector will be presented, too.

• Artikel i tidskrift

Babusci, D.; Czyż, H.; Gonnella, F.; Ivashyn, S. et al.

### On the possibility to measure the π 0→γγ decay width and the γ ∗ γ→π 0 transition form factor with the KLOE-2 experiment

Ingår i European Physical Journal C, s. 1917-, 2012.

• Artikel i tidskrift

Mascolo, Matteo; Caldeira Balkeståhl, Li; Höistad, Bo; Johansson, Tord et al.

### Gamma-gamma physics at KLOE/KLOE-2

Ingår i Journal of Physics, Conference Series, s. 012014-, 2012.

• Artikel i tidskrift

Leupold, Stefan; Terschlüsen, Carla

### Towards an effective field theory for vector mesons

Ingår i PoS - Proceedings of Science, 2012.

• Artikel i tidskrift

Terschlusen, Carla; Leupold, Stefan; Lutz, M. F. M.

### Electromagnetic transitions in an effective chiral Lagrangian with the eta ' and light vector mesons

Ingår i European Physical Journal A, s. 190-, 2012.

#### Abstract

We consider the chiral Lagrangian with a nonet of Goldstone bosons and a nonet of light vector mesons. The mixing between the pseudoscalar mesons eta and eta' is taken into account. A novel counting scheme is suggested that is based on hadrogenesis, which conjectures a mass gap in the meson spectrum of QCD in the limit of a large number of colors. Such a mass gap would justify to consider the vector mesons and the eta' meson as light degrees of freedom. The complete leading-order Lagrangian is constructed and discussed. As a first application it is tested against electromagnetic transitions of light vector mesons to pseudoscalar mesons. Our parameters are determined by the experimental data on photon decays of the omega, phi and eta' mesons. In terms of such parameters we predict the corresponding decays into virtual photons with either dielectrons or dimuons in the final state.

• Artikel i tidskrift

Wadsworth, R.; Singh, B. S. N.; Liu, Z.; Grawe, H. et al.

### Spin-gap isomer in 96Cd

Ingår i Journal of Physics, Conference Series, s. 012074-, 2012.

#### Abstract

Evidence has been obtained for the existence of the long predicted 16 + spin-gap isomer in 96Cd. The decay of the isomer was identified and studied following the use of an 850 MeV/u beam of 124Xe impinging on a Be target and the fragment recoil separator at the GSI Laboratory. Gamma decays from the fragments were detected using the RISING gamma ray array, in its stopped beam configuration, plus a silicon active stopper. The data obtained have been compared with shell model predictions, which indicate that the isoscalar neutron-proton interaction plays a key role in the formation of the isomer.

• Artikel i tidskrift

Söderström, Pär-Anders; Recchia, F.; Nyberg, Johan; Gadea, A. et al.

### High-spin structure in K-40

Ingår i Physical Review C. Nuclear Physics, s. 054320-, 2012.

#### Abstract

High-spin states of K-40 have been populated in the fusion-evaporation reaction C-12(Si-30,np)K-40 and studied by means of gamma-ray spectroscopy techniques using one triple-cluster detector of the Advanced Gamma Tracking Array at the Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro. Several states with excitation energy up to 8 MeV and spin up to 10(-) have been discovered. These states are discussed in terms of J = 3 and T = 0 neutron-proton hole pairs. Shell-model calculations in a large model space have shown good agreement with the experimental data for most of the energy levels. The evolution of the structure of this nucleus is here studied as a function of excitation energy and angular momentum.

• Artikel i tidskrift

Adlarson, Patrik; Augustyniak, W.; Bardan, W.; Bashkanov, M. et al.

### Abashian-Booth-Crowe resonance structure in the double pionic fusion to He-4

Ingår i Physical Review C. Nuclear Physics, s. 032201-, 2012.

#### Abstract

Exclusive and kinematically complete high-statistics measurements of the double pionic fusion reaction dd -> He-4 pi(0)pi(0) have been performed in the energy range 0.8-1.4 GeV covering thus the region of the Abashian-Booth-Crowe effect, which denotes a pronounced low-mass enhancement in the pi pi invariant mass spectrum. The experiments were carried out with the WASA detector setup at the cooler synchrotron at Forshungszentrum Julich GmbH. Similar to the observation in the basic pn -> d pi(0)pi(0) reaction, the data reveal a correlation between the ABC effect and a resonancelike energy dependence in the total cross section. The maximum occurs at m = 2.37 GeV + 2m(N), i.e., at the same position as in the basic reaction. The observed resonance width Gamma approximate to 160 MeV can be understood from broadening due to Fermi motion of the nucleons in initial and final nuclei together with collision damping. Differential cross sections are described equally well by the hypothesis of a pn resonance formation during the reaction process.

• Artikel i tidskrift

Palacz, M.; Nyberg, Johan; Grawe, H.; Sieja, K. et al.

### N=50 core excited states studied in the 4696Pd50 nucleus

Ingår i Physical Review C. Nuclear Physics, s. 014318-, 2012.

#### Abstract

The four-proton hole Pd-96 neighbor of the doubly-magic Sn-100 nucleus was studied in-beam, using a fusion-evaporation reaction of a Ni-58 beam on a Sc-45 target. States of Pd-96 were established up to an excitation energy of 9707 keV. A core-excited odd-parity isomer with T-1/2 = 37.7(1.1) ns was identified. Shell model calculations were performed in four different model spaces. Even-parity states of Pd-96 are very well reproduced in large-scale shell model (LSSM) calculations in which excitations are allowed of up to five g(9/2) protons and neutrons across the N = Z = 50 gap, to the g(7/2), d(5/2), d(3/2), and s(1/2) orbitals. The odd-parity isomer can be only qualitatively interpreted though, employing calculation in the full fpg shell model space, with just one particle-hole core excitation.

Open access
• Artikel i tidskrift

Singh, B. S. Nara; Brock, T. S.; Wadsworth, R.; Grawe, H. et al.

### Influence of the np interaction on the beta decay of Pd-94

Ingår i Physical Review C. Nuclear Physics, s. 041301-, 2012.

#### Abstract

We present results from stopped beam rare isotope spectroscopic investigations at the GSI (RISING) experiment based on the detection of gamma-ray transitions following the beta decay of Pd-94. A comparison between the measured low-lying level scheme of Rh-94 and the prediction from shell-model calculations reveals the important roles of the g(7/2) and g(9/2) orbitals in explaining the structural features. The low values of the Gamow-Teller strengths B(GT) can be attributed to the influence of the neutron-proton interaction, which gives rise to an increased seniority mixing for the nuclear states, thereby leading to a fragmentation of the strength to several daughter levels. These results provide further strong indications that Pd-94 resides in the middle of a structural transition region in the Pd isotopes as the N = Z line is approached.

Open access
• Artikel i tidskrift

### Study of the decay eta -> pi(+)pi(-)pi(0) with WASA-at-COSY

Ingår i Physica Scripta, s. 014001-, 2012.

#### Abstract

Recently, a large statistics sample of approximately 3 x 10(7) eta decays was collected with the Wide Angle Shower Apparatus (WASA) detector at COoler SYnchrotron (COSY) using the pd -> He-3 eta reaction at the proton kinetic energy of 1 GeV. These data are being used to study the not so rare eta decays involving charged pions, such as eta -> pi(+)pi(-)pi(0). This decay proceeds mainly via a strong isospin violating contribution, where the decay width is proportional to the light quark mass difference squared, (m(d) - m(u))(2). The status of the analysis is presented, which preliminarily gives 1.8 x 10(5) eta -> pi(+)pi(-)pi(0) candidates in the Dalitz plot.

• Artikel i tidskrift

Söderström, Pär-Anders

### Nuclear deformations in the region of the A=160 r-process abundance peak

Ingår i Physica Scripta, s. 014038-, 2012.

#### Abstract

In the abundance spectrum of r-process nuclei the most prominent features are the peaks that form when the r-process flow passes through the closed neutron shells. However, there are also other features in the abundance spectrum that cannot be explained by shell effects; for example, the peak in the region of the rare-earth nuclei around mass A = 160. It has been argued that this peak is related to the deformation maximum of the neutron-rich isotopes. In recent years, both experimental and theoretical work has been carried out to study the deformation of neutron-rich rare-earth nuclei and to search for the point of maximum deformation. This work has focused on the nuclei around Dy-170 with the aim of understanding the evolution of collectivity in the neutron shell with 82 < N < 126. These investigations will be discussed in terms of the Harris parameters of the variable moment of inertia model. Finally, we will discuss the possibility of reaching further into the neutron-rich rare-earth region in the future at the new experimental facilities using radioactive beams.

• Artikel i tidskrift

Wolke, Magnus

### Symmetries and hadron spectroscopy with WASA-at-COSY

Ingår i Physica Scripta, s. 014043-, 2012.

#### Abstract

Experiments with the WASA detector focus on studies of symmetries and symmetry breaking patterns in hadronic systems as well as hadron spectroscopy. The goal is to investigate the properties of quantum chromodynamics in the non-perturbative regime, where confinement and chiral symmetry breaking are distinctive phenomena. Here, we report latest results on decays of the pseudoscalar eta meson and exclusive data on pi pi production which might indicate the existence of a new resonance in the proton-neutron and Delta Delta systems.

• Artikel i tidskrift

Fäldt, Göran

### Meson production in high-energy electron-nucleus scattering

Ingår i Physical Review C. Nuclear Physics, s. 024611-, 2012.

#### Abstract

Pseudoscalar mesons can be produced and studied in high-energy electron-nucleus scattering. We review and extend our previous theoretical analysis of meson production in the nuclear Coulomb field. The P -> gamma gamma decay rates are most directly determined for mesons produced in the double-Coulomb region where both photons are nearly real, and provided the hadronic-background contributions remain small. The larger the mass of the meson the higher the electron energy needed to assure such favorable conditions.

• Artikel i tidskrift

Hinke, C. B.; Boehmer, M.; Boutachkov, P.; Faestermann, T. et al.

### Superallowed Gamow-Teller decay of the doubly magic nucleus 100Sn

Ingår i Nature, s. 341-345, 2012.

#### Abstract

The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During beta(+)-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of Sn-100, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the beta-decay of Sn-100, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear beta-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, In-100, are well reproduced by modern, large-scale shell model calculations.

Open access
• Artikel i tidskrift

Hilger, T.; Thomas, R.; Kaempfer, B.; Leupold, Stefan

### The impact of chirally odd condensates on the rho meson

Ingår i Physics Letters B, s. 200-206, 2012.

#### Abstract

Based on QCD sum rules we explore the consequences of a scenario for the rho meson, where the chiral symmetry breaking condensates are set to zero whereas the chirally symmetric condensates remain at their vacuum values. This clean-cut scenario causes a lowering of the rho spectral moment by about 120 MeV. The complementarity of mass shift and broadening is discussed. A simple parametrization of the rho spectral function leads to a width of about 280 MeV if no shift of the peak position is assumed.

• Artikel i tidskrift

Akkoyun, S.; Algora, A.; Alikhani, B.; Ameil, F. et al.

### AGATA -Advanced GAmma Tracking Array

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 26-58, 2012.

#### Abstract

The Advanced GAmma Tracking Array (AGATA) is a European project to develop and operate the next generation gamma-ray spectrometer. AGATA is based on the technique of gamma-ray energy tracking in electrically segmented high-purity germanium crystals. This technique requires the accurate determination of the energy, time and position of every interaction as a gamma ray deposits its energy within the detector volume. Reconstruction of the full interaction path results in a detector with very high efficiency and excellent spectral response. The realisation of gamma-ray tracking and AGATA is a result of many technical advances. These include the development of encapsulated highly segmented germanium detectors assembled in a triple cluster detector cryostat, an electronics system with fast digital sampling and a data acquisition system to process the data at a high rate. The full characterisation of the crystals was measured and compared with detector-response simulations. This enabled pulse-shape analysis algorithms, to extract energy, time and position, to be employed. In addition, tracking algorithms for event reconstruction were developed. The first phase of AGATA is now complete and operational in its first physics campaign. In the future AGATA will be moved between laboratories in Europe and operated in a series of campaigns to take advantage of the different beams and facilities available to maximise its science output. The paper reviews all the achievements made in the AGATA project including all the necessary infrastructure to operate and support the spectrometer.

• Artikel i tidskrift

Jaworski, G.; Palacz, M.; Nyberg, Johan; Angelis, G. de et al.

### Monte Carlo simulation of a single detector unit for the neutron detector array NEDA

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 64-72, 2012.

#### Abstract

A study of the dimensions and performance of a single detector of the future neutron detector array NEDA was performed by means of Monte Carlo simulations, using GEANT4. Two different liquid scintillators were evaluated: the hydrogen based BC501A and the deuterated BC537. The efficiency and the probability that one neutron will trigger a signal in more than one detector were investigated as a function of the detector size. The simulations were validated comparing the results to experimental measurements performed with two existing neutron detectors, with different geometries, based on the liquid scintillator BC501

Open access
• Artikel i tidskrift

### Exclusive measurement of the eta -> pi(+) pi(-) gamma decay

Ingår i Physics Letters B, s. 243-249, 2012.

#### Abstract

An exclusive measurement of the decay eta -> pi(+) pi(-) gamma has been performed at the WASA facility at COSY. The eta mesons were produced in the fusion reaction pd -> He-3 X at a proton beam momentum of 1.7 GeV/c. Efficiency corrected differential distributions have been extracted based on 13 960 +/- 140 events after background subtraction. The measured pion angular distribution is consistent with a relative p-wave of the two-pion system, whereas the measured photon energy spectrum was found at variance with the simplest gauge invariant matrix element of eta -> pi(+) pi(-) gamma. A parameterization of the data can be achieved by the additional inclusion of the empirical pion vector form factor multiplied by a first-order polynomial in the squared invariant mass of the pi(+) pi(-) system.

• Artikel i tidskrift

Stollenwerk, F.; Hanhart, C.; Kupsc, Andrzej; Meissner, U.-G. et al.

### Model-independent approach to η→π+π−γ and η′→π+π−γ

Ingår i Physics Letters B, s. 184-190, 2012.

#### Abstract

We present a new, model-independent method to analyze radiative decays of mesons to a vector, isovector pair of pions of invariant mass square below the first significant pi pi threshold in the vector channel. It is based on a combination of chiral perturbation theory and dispersion theory. This allows for a controlled inclusion of resonance physics without the necessity to involve vector meson dominance explicitly. As an example, the method is applied to an analysis of the reactions eta -> pi(+)pi(-)gamma and eta' -> pi(+)pi(-)gamma.

• Artikel i tidskrift

### pi(0)pi(0) Production in proton-proton collisions at T-p=1.4 GeV The WASA-at-COSY Collaboration

Ingår i Physics Letters B, s. 256-262, 2012.

#### Abstract

The reaction pp -> pp pi(0)pi(0) has been investigated at a beam energy of 1.4 GeV using the WASA-at-COSY facility. The total cross section is found to be (324 +/- 21(systematic) +/- 58(normalization)) mu b. In order to study the production mechanism, differential kinematic distributions have been evaluated. The differential distributions indicate that both initial state protons are excited into intermediate Delta(1232) resonances, each decaying into a proton and a single pion, thereby producing the pion pair in the final state. No significant contribution of the Roper resonance N*(1440) via its decay into a proton and two pions is found.

• Artikel i tidskrift

Archilli, F.; Babusci, D.; Badoni, D.; Balwierz, I. et al.

### Search for a vector gauge boson in phi meson decays with the KLOE detector KLOE-2 Collaboration

Ingår i Physics Letters B, s. 251-255, 2012.

#### Abstract

The existence of a light dark force mediator has been tested with the KLOE detector at DA Phi NE. This particle, called U. is searched for using the decay chain phi -> eta U, eta -> pi(+)pi(-)pi(0), U -> e(+)e(-). No evidence is found in 1.5 fb(-1) of data. The resulting exclusion plot covers the mass range 5 < M-U < 470 MeV, setting an upper limit on the ratio between the U boson coupling constant and the One structure constant, alpha'/alpha, of <= 2 x 10(-5) at 90% C.L. for 50 < M-U < 420 MeV.

• Artikel i tidskrift

Föhl, K; Düren, M; Koch, P; Zühlsdorf, M et al.

### The WASA focussing light guide disc DIRC

Ingår i Journal of Instrumentation, s. C01002-, 2012.

#### Abstract

Two Disc DIRC prototypes have been designed and built and are shortly being tested with proton test beams. Different in design details, both aim to provide the WASA-at-COSY experiment with a particle velocity measurement that improves the missing mass resolution. This paper shows the difference in concept between these two designs and also compares to designs that have been proposed for PANDA.

• Artikel, forskningsöversikt

Terschlüsen, Carla; Leupold, Stefan

### Electromagnetic transition form factors of mesons

Ingår i Progress in Particle and Nuclear Physics, s. 401-405, 2012.

#### Abstract

Using a counting scheme which treats pseudoscalar and vector mesons on equal footing, the decays of the narrow light vector mesons omega and phi into a dilepton and a pseudoscalar pi(0)-meson or eta-meson, respectively, are calculated. Thereby, all required parameters could be determined by other reactions so that one has predictive power for the considered decays. The calculated partial decay widths are in very good agreement with the experimental data.

• Artikel, forskningsöversikt

Hilger, T.; Buchheim, T.; Kaempfer, B.; Leupold, Stefan

### Four-quark condensates in open-charm chiral QCD sum rules

Ingår i Progress in Particle and Nuclear Physics, s. 188-193, 2012.

#### Abstract

Recently, in Hilger et al. (2011) [1] QCD sum rules for chiral partners in the open-charm meson sector have been presented at nonzero baryon net density or temperature up to and including mass dimension 5. Referring to this, details concerning the cancelation of infrared divergences are presented and important technical and conceptional ingredients for an incorporation of four-quark condensates beyond factorization and of other mass dimension 6 condensates are collected.

• Artikel i tidskrift

Nahrgang, Marlene; Leupold, Stefan; Bleicher, Marcus

### Equilibration and relaxation times at the chiral phase transition including reheating

Ingår i Physics Letters B, s. 109-116, 2012.

#### Abstract

We investigate the relaxational dynamics of the order parameter of chiral symmetry breaking, the sigma mean-field, with a heat bath consisting of quarks and antiquarks. A semiclassical stochastic Langevin equation of motion is obtained from the linear sigma model with constituent quarks. The equilibration of the system is studied for a first order phase transition and a critical point, where a different behavior is found. At the first order phase transition we observe the phase coexistence and at a critical point the phenomenon of critical slowing down with large relaxation times. We go beyond existing Langevin studies and include reheating of the heat bath by determining the energy dissipation during the relaxational process. The energy of the entire system is conserved. In a critical point scenario we again observe critical slowing down.

• Artikel i tidskrift

von Wurtemberg, K. Marcks; Geren, L.; Lundberg, O.; Tegner, P-E et al.

### The response of lead-tungstate scintillators (PWO) to photons with energies in the range 13 MeV-64 MeV

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 36-43, 2012.

#### Abstract

The response of a matrix of 25 lead tungstate (PWO) scintillator detectors, operated at -25 degrees C, to photons in the range 13 MeV-64 MeV has been measured at the tagged-photon facility at MAX-lab, Lund. The tapered PWO crystals, each with a length of 200 mm and a cross-section of 24.4 x 24.4 mm(2) in the front end, read out by 19 mm photomultiplier tubes, were arranged in a 5 x 5 matrix. The response was measured for photons directed towards the centre of the central crystal as well as for photons directed towards the corner of the central crystal, where four crystals meet. The obtained energy resolution surpasses what has been published so far and is close to the limit given by Poisson statistics and escaped energy. For photons directed towards the centre(corner) of the central crystal the relative energy resolution, defined as (FWHM/2.35)/E-gamma, decreases from 7.3%(11.0%) at E-gamma = 13 MeV to 3.3%(3.6%) at E-gamma = 64 MeV. The reconstructed point of impact of a photon in this energy range is determined with an uncertainty (one standard deviation) of 7.3 +/- 0.1 mm.

• Artikel i tidskrift

Nara Singh, B. S.; Wadsworth, R.; Boutachkov, P.; Blazhev, A. et al.

### Exotic nuclear studies around and below Aâ=â100

Ingår i AIP Conference Proceedings, s. 19-24, 2011.

• Konferensbidrag

Vandone, V; Nyberg, Johan

### Order-to-chaos transition in warm rotating 174W nuclei

Ingår i Proc. Int. School of Physics Enrico Fermi, s. 427-, 2011.

• Artikel i tidskrift

Boutachkov, P; Braun, N; Brock, T; Singh, B S Nara et al.

### Isomer and Î² -decay spectroscopy of T z =1 isotopes below the N=Z=50 shell gap

Ingår i Journal of Physics: Conference Series, 2011.

#### Abstract

The RISING setup at the GSI-FRS facility was used to investigate the isomer and beta decays in N Z 50 Cd, Ag and Pd isotopes. A preliminary analysis of the data has revealed new results on the Tz=1, 94 Pd, 96 Ag and 98 Cd isotopes. In 94 Pd a new high-spin isomer was observed, whilst in 96 Ag 3 new isomeric states were identified, including core-excited states. In 98 Cd a new high-energy isomeric Î³-ray transition is observed, thus enabling us to confirm the previous spin assignment for the core-excited 12 + isomer.

• Konferensbidrag

Crespi, F. C. L.; Avigo, R.; Camera, F.; Benzoni, G. et al.

### Response of AGATA segmented HPGe detectors to gamma-rays up to 15.1 MeV

Ingår i Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2011 IEEE, s. 1147-1149, 2011.

• Artikel i tidskrift

Söderström, P. -A; Recchia, F.; Nyberg, Johan; Al-Adili, A. et al.

### Interaction position resolution simulations and in-beam measurements of the AGATA HPGe detectors

Ingår i Nuclear Instruments and Methods in Physics Research Section A, s. 96-109, 2011.

#### Abstract

The interaction position resolution of the segmented HPGe detectors of an AGATA triple cluster detector has been studied through Monte Carlo simulations and in an in-beam experiment. A new method based on measuring the energy resolution of Doppler-corrected γ ‐ ray