Doktorsavhandlingar

Doktorsavhandlingar och licentiatavhandlingar

  • Doktorsavhandling, monografi

    Pettersson, Joachim

    From Strange to Charm: Meson production in electron-positron collisions

    Abstract

    Decays of pseudoscalar mesons into a lepton-antilepton pair are very rare within the Standard Model since they cannot proceed via a single photon process. The C-even neutral mesons can be produced in electron-positron collisions by a two-photon intermediate state. Due to the rarity the of Pl+l- decays, measurements of their branching fractions are sensitive to physics beyond the Standard Model. This thesis report the first search for the process e+e-→ηusing the K±K0Sπ±K+0 and K+K-η final states to determine the branching fraction of the time reverse process ηc→e+e-. This study is an extension of the previous measurements of π0→e+e- and η→μ+μ-, and the upper limits set for η→e+e- and η'→μ+μ-. The analysis presented in this thesis uses data collected by the BESIII detector situated at the e+e- collider BEPCII in Beijing, China. The data set consist of 22 center-of-mass energy points between 2.000 to 3.080 GeV where a data point at the energy 2.981 GeV was recorded specifically for this study. Monte Carlo simulations are used to develop selection criteria and to estimate selection efficiency and corrections due to initial state radiation.

    No signal from e+e-→ηc was observed. Therefore, an upper limit is set for the branching fraction of the process ηce+e- using a profile likelihood method. The result for the 90% C.L. limit is BF(ηce+e-)<8.1×10-7 where systematic uncertainties are included. 

    In addition to the search for ηc→e+e-, the cross sections of the processes e+e-→K±K0π±e+e-→K+K-π0 and e+e-→K+K-η are measured at all 22 energies. These cross section measurements can be used to search for exotic resonances and to achieve an understanding of exotic states such as Y(2175) and X(2370).

    Open access
  • Doktorsavhandling, monografi

    Pszczel, Damian

    Search for a new light boson in meson decays

    Abstract

    The subject of the presented work lies in the field of experimental particle physics. The main topic is the study of e+ e pairs from η meson decays. The data sample used in this work was collected by the WASA-at-COSY collaboration in proton-proton collisions at 1.4 GeV kinetic beam energy. The experiment took place in 2012 at Forschungzentrum Jülich in Germany at the COSY storage ring. An internal proton beam interacted with a pellet target of frozen hydrogen.

    We implemented a set of selection criteria in order to extract the η → e+ e γ event candidates. This is a rare electromagnetic decay of the η meson with branching ratio equal to 6.9·10−3. The resulting set of events served as the basis for three analyses.

    First, we extracted the η transition form factor that is a function depending on the inner quark and gluon structure of the meson. We implemented a specific method to reduce the contribution of background channels from direct pion production.

    The second analysis was the search for a narrow structure on the e+ e invariant mass in the selected sample of η → e+ e γ candidates. Many theoretical models and some astrophysical and particle physics measurements suggest the existence of a new boson, also called the dark photon, that couples to both dark and to Standard Model particles. This particle would decay to e+ e pairs of well-defined mass and therefore could be detected by looking for narrow peaks in the e+ e invariant mass spectra. Since no statistically significant signal was observed, we set an upper limit on the coupling parameter ε2.

    The third objective of this work was to select a sample of η → e+ e candidates. This is a very rare decay and therefore sensitive to physics beyond the Standard Model. No signal from η → e+ e was observed, therefore we were able to set an upper limit on the branching ratio for this decay.

    Open access
  • Doktorsavhandling, sammanläggning

    Ghaderi, Hazhar

    The interplay between quark and hadronic degrees of freedom and the structure of the proton

    Abstract

    We study the low-energy sector of the strong interaction which is the least understood part of the Standard Model, the theory that describes the interactions of all known particles. The ideal particles for this study are the proton and the neutron, collectively called the nucleon. They make up the nucleus of all the atoms of our world and understanding them has been of high priority ever since their discovery. We show that one cannot neglect the effects of other hadrons, such as neutrons and pions when studying the proton. A large part of the proton's hadronic wavefunction is shown to consist of the wavefunctions of other hadrons. In other words, when probing the proton there is a sizeable probability that one is probing some other hadron surrounding the proton as a quantum fluctuation.

    The nucleon itself consists of elementary particles known as quarks and gluons, collectively called partons. Exactly how the properties of these partons make up the properties of the nucleon has been the subject of active research ever since their discovery. Two main issues are the flavor asymmetry of the proton sea and the spin structure of the nucleon. To address these questions we study the interplay between the partonic and hadronic degrees of freedom. We introduce a model based on a convolution between hadronic quantum fluctuations as described by chiral perturbation theory, and partonic degrees of freedom motivated by a physical model of the nucleon having only few physically constrained parameters.

    We present the hadronic distribution functions and the parton distribution functions. The results are in agreement with a large set of experimental data. These include the structure functions of the proton and the neutron. Agreement with the sum rules of the spin structure functions offers new insight into the spin structure of the nucleon.

    Open access
  • Doktorsavhandling, monografi

    Heijkenskjöld, Lena

    Hadronic Decays of the ω Meson

    Abstract

    Two decay channels of the ω(782) meson, into π+π-π0 and π+π-, are studied. The dynamics of the three-pion channel is represented using a two-dimensional distribution, called a Dalitz plot. A high-statistics Dalitz plot distribution is needed to test theoretical predictions and increase understanding of the decay mechanism. The isospin-breaking two-pion decay gives insight into the ρ-ω mixing. The ω→π+π- decay has previously been studied in π+π- spectra in high statistics e+e- experiments and with lower statistics in hadroproduction experiments. The collected evidence indicates that the resulting interference pattern strongly depends on the production reaction.

    In 2011 an experiment to investigate ω hadronic decays in pd→3Heω reaction was performed with the WASA detector. Two studies based on the collected data are included in this thesis. In the first, the dominant decay channel ω→π+π-π0 is selected and two experimental Dalitz plot distributions are created. Each distribution corresponds to one of the two incident beam energies used in the experiment. A fit to the Dalitz plots is performed using a parametrisation including the expected P-wave shape. The result indicates an onset of the intermediate ρ in the two-pion channel, as predicted by theoretical models. The efficiency corrected Dalitz plot bin contents are reported to facilitate comparison to theoretical predictions by direct fits to the experimental data. In the second study, the ω→π+π- decay channel is selected. For events with a 3Heπ+π- final state, the 3He missing mass is constructed in search for the ρ-ω interference pattern in pd production. No significant deviations around the ω mass position was found. Dedicated studies using experimental data to estimate background contribution and to extract signal acceptance shows that the background is too large to observe the expected signal with the collected data sample.

    The last part of the thesis presents pre-studies for using data collected at the KLOE detector for an ω→π+π-π0 Dalitz plot analysis. Since the ω mesons are produced in the e+e-→ωπ0 reaction, the study focuses on the impact of the π00 interference.

    Open access
  • Doktorsavhandling, sammanläggning

    Terschlüsen, Carla

    Theoretical Studies of Hadronic Reactions with Vector Mesons

    Abstract

    Aiming at a systematic inclusion of pseudoscalar and vector mesons as active degrees of freedom in an effective Lagrangian, studies have been performed in this thesis concerning the foundations of such an effective Lagrangian as well as tree-level and beyond-tree-level calculations. Hereby, vector mesons are described by antisymmetric tensor fields.

    First, an existing power counting scheme for both pseudoscalar and vector mesons is extended to include the pseudoscalar-meson singlet in a systematic way. Based on this, tree-level calculations are carried out which are in good agreement with the available experimental data and several processes are predicted. In particular, the ω-π0 transition form factor is in better agreement with experimental data than the prediction done in the vector-meson-dominance model. Furthermore, a Lagrangian with vector mesons is used together with the leading contributions of chiral perturbation theory in order to calculate tree-level reactions in the sector of odd intrinsic parity. It turns out that both the Lagrangian with vector mesons and the Lagrangian of chiral perturbation theory are needed to describe experimental data.

    Additionally, a feasibility check for one-loop calculations with pseudoscalar and vector mesons in the loop is performed. Thereby, only a limited number of interaction terms in the Lagrangian with vector mesons is used. The results are used to both renormalise the low-energy constants of chiral perturbation theory up to chiral order Q4 and to determine the influence of loops with vector mesons on masses and decay constants of pseudoscalar mesons.

    Open access
  • Doktorsavhandling, monografi

    Caldeira Balkeståhl, Li

    Measurement of the Dalitz Plot Distribution for η→π+ππ0 with KLOE

    Abstract

    The mechanism of the isospin violating η→π+ππ0 decay is studied in a high precision experiment using a Dalitz plot analysis. The process is sensitive to the difference between up and down quark masses. The measurement provides an important input for the determination of the light quark masses and for the theoretical description of the low energy strong interactions.

    The measurement was carried out between 2004 and 2005 using the KLOE detector at the DAΦNE e+e collider located in Frascati, Italy. The data was collected at a center of mass energy corresponding to the φ-meson peak (1019.5 MeV) with an integrated luminosity of 1.6 fb−1. The source of the η-mesons is the radiative decay of the φ-meson: e+e→φ→ηγ, resulting in the world’s largest data sample of about 4.7·106 η→π+ππ0 decay events.

    In this thesis, the KLOE Monte Carlo simulation and reconstruction programs are used to optimize the background rejection cuts and to evaluate the signal efficiency. The background contamination in the final data sample is below 1%. The data sample is used to construct the Dalitz plot distribution in the normalized dimensionless variables X and Y. The distribution is parametrized by determining the coefficients of the third order polynomial in the X and Y variables (so called Dalitz plot parameters). The statistical accuracy of the extracted parameters is two times better than any of the previous measurements. In particular the contribution of the X2Y term is found to be different from zero with a significance of approximately 3σ. The systematic effects are studied and found to be of the same size as the statistical uncertainty. The contribution of the terms related to charge conjugation violation (odd powers of the X variable) and the measured charge asymmetries are consistent with zero.

    The background subtracted and acceptance corrected bin contents of the Dalitz plot distribution are provided to facilitate direct comparison with other experiments and with theoretical calculations.

    Open access
  • Doktorsavhandling, monografi

    Pyszniak, Andrzej

    Development and Applications of Tracking of Pellet Streams

    Abstract

    The development of a system for optical tracking of frozen hydrogen microsphere targets (pellets) was done. It is intended for the upcoming hadron physics experiment PANDA at FAIR, Darmstadt, Germany. Knowledge of the interaction position, obtained with this system, will improve background rejection, precision of particle track reconstruction and will also help distinguish between primary and secondary vertices. Investigations of pellet detection conditions and pellet stream parameters were performed at Uppsala Pellet Test Station located at The Svedberg Laboratory. Various illumination and detection conditions were checked and optimized. The gained knowledge has been used to develop Monte Carlo procedures simulating experiments with pellets. Then simulations of pellet tracking were carried out including the constraints from the PANDA setup. The performance of the tracking was checked for various pellet stream and pellet detection conditions. Two procedures of pellet track reconstruction were developed – a fast procedure and a high efficiency procedure. The studies were done for one tracking section (just below pellet generator) and for two sections (the second just above pellet dump) and showed that the resolution of the tracking system can be better than 100 μm (sigma) in each direction and that the interaction point will be reconstructed for 70-95% of hadronic events, for suitable pellet stream and detection conditions. Usage of pellet tracking information in the hadronic data analysis was discussed, concerning the data taking, particle track reconstruction together with the PANDA micro vertex detector, hadronic event classification and treatment of the various classes. Test measurements with the WASA setup at FZJ, Jülich, Germany were done to check how the information about the number of pellets in the accelerator beam region can be used in the hadronic data analysis. Instantaneous rates of WASA "elastic" triggers were used for classification of hadronic events as coming from pellets or from a background. The study clearly showed that one can distinguish between the two event classes. The study gave experience in using two different systems synchronized with each other – the experiment's DAQ and another system that works with a much longer time scale – similar to the pellet tracking system.

    Ett system för optisk spårning av frysta mikrosfärer av väte (pelletar) har utvecklats för användning i det kommande hadronfysikexperimentet PANDA vid FAIR, Darmstadt i Tyskland. Kunskapen om positionen för växelverkan som fås med hjälp av detta system kommer att förbättra möjligheten att diskriminera mot bakgrund, att öka precisionen i partikelspårsrekonstruktionen och kommer också att hjälpa till att skilja mellan primära och sekundära växelverkanspunkter. Undersökningar av pelletdetektionsmöjligheter och pelletströmmens egenskaper har gjorts vid Uppsala Pellet Test Station vid The Svedberglaboratoriet. Olika belysnings och detektionsvillkor har testats och optimerats. Den erhållna kunskapen har använts för att utveckla en Monte-Carlo procedur för att kunna simulera de olika experimenten med pelletar. Därefter genomfördes simuleringar av förväntade pelletspårningsprestanda för PANDA uppställningen. Prestanda och upplösning av spårningen kontrollerades för olika pelletsström och detektionsförhållanden. Två procedurer för spårrekonstruktion utvecklades för studien – en snabbare och en med högsta möjliga effektivitet. Den kommer att kunna användas i dataanalysen när fullskalig pelletspårning används ihop med ett partikeldetektorsystem. Studien gjordes för två fall, dels för en spårningssektion (placerad just under pelletgeneratorn) och dels med ytterligare en sektion (placerad just ovanför pelletdumpen). Studien visade att positionsupplösningen som förväntas från spårningssystemet är bättre än 100 μm (sigma) i varje riktning och att växelverkanspunkten kan rekonstrueras för 70-95% av de hadroniska händelserna, för lämpliga pelletströms- och detektionsvillkor. Användningen av pelletspårningsinformationen i analysen av hadroniska händelsedata diskuterades m.a.p. datainsamling, m.a.p. partikelspårsrekonstruktion ihop med PANDA's mikrovertexdetektor och m.a.p. klassificering av händelser. Det gjordes testmätningar med WASA-uppställningen vid FZJ, Jülich i Tyskland för att se hur informationen om antalet pelletar i acceleratorstrålområdet kan användas i experimentets dataanalys. Den momentana frekvensen av elastiska spridningshändelser användes för en grov klassificering av händelsers ursprung såsom varande antingen från en pellet eller från någon källa till bakgrund. Studien visade klart att man kan skilja de båda klasserna åt. Studien gav också erfarenhet av hur man kan använda två synkroniserade datasystem – experimentets datainsamlingssystem och ett annat system som arbetar med en mycket längre tidsskala – liknande pelletspårningssystemets.

    Wykonane zostały prace nad rozwojem systemu pozwalającego na optyczne śledzenie zamarzniętych wodorowych mikrokulek (pelletów). System przeznaczony jest do zastosowania w planowanym eksperymencie z dziedziny fizyki hadronowej, PANDA (FAIR, Darmstadt, Niemcy). Wiedza o położeniu punktu interakcji, uzyskana dzięki temu systemowi, poprawi redukcję tła, precyzję rekonstrukcji torów cząstek, a także pomoże w rozróżnianiu pierwotnych i wtórnych wierzchołków interakcji. Na Uppsalskiej Stacji Pelletowej (Uppsala Pellet Test Station) umieszczonej w Laboratorium The Svedberga, przeprowadzone zostały badania warunków detekcji pelletów i parametrów strumienia pelletowego. Różne warunki oświetlenia oraz detekcji pelletów zostały sprawdzone i zoptymalizowane. Uzyskana wiedza została użyta do stworzenia procedur Monte Carlo symulujących eksperymenty z pelletami. W następnym kroku przeprowadzone zostały symulacje śledzenia pelletów biorące pod uwagę więzy narzucone przez konstrukcję systemu PANDA. Wydajność systemu sprawdzona została dla różnych warunków strumienia pelletowego i detekcji pelletów. Stworzone zostały dwie procedury rekonstrukcji torów pelletowych -- procedura szybka i procedura wysokoefektywna. Badania przeprowadzone zostały dla jednej sekcji śledzącej (bezpośrednio poniżej generatora pelletów) oraz dla dwóch sekcji (druga bezpośrednio nad miejscem zbierania pelletów) i pokazały, że rozdzielczość systemu śledzenia może być lepsza niż 100 μm (sigma) w każdym z kierunków oraz że punkt interakcji będzie zrekonstruowany dla 70-95\% zdarzeń hadronowych, dla odpowiednich warunków strumienia pelletów i warunków detekcji. Użycie informacji ze śledzenia pelletów w analizie danych hadronowych zostało przedyskutowane uwzględniając proces zbierania danych, rekonstrukcję torów cząstek we współpracy z mikrodetektorem wierzchołków systemu PANDA, klasyfikację zdarzeń hadronowych oraz sposób traktowania różnych klas zdarzeń. Pomiary testowe z użyciem detektora WASA (FZJ, Jülich, Niemcy) zostały dokonane w celu sprawdzenia jak informacja o liczbie pelletów w obszarze wiązki może zostać użyta w analizie danych hadronowych. Chwilowe częstotliwości "elastycznych" triggerów systemu WASA zostały użyte w celu klasyfikacji zdarzeń hadronowych jako pochodzących z interakcji wiązka-pellet lub wiązka-tło. Badania wykazały iż możliwe jest rozróżnienie między tymi dwoma klasami zdarzeń. Uzyskano również doświadczenie w używaniu dwóch różnych systemów zsynchronizowanych ze sobą – eksperymentalnego systemu zbierania danych oraz innego systemu, działającego w znacznie dłuższej skali czasowej – podobnie do systemu śledzenia pelletów.

    Open access
  • Doktorsavhandling, monografi

    Adlarson, Patrik

    Studies of the Decay η→π+π-π0 with WASA-at-COSY

    Abstract

    In 2008 a large statistics sample of approximately 1·107 η-decays has been collected with the WASA detector at COSY using the pd→3Heη reaction at the beam kinetic energy of 1 GeV. These data are being used to study the not so rare η decays involving charged pions, like η→π+π-π0. This decay proceeds mainly via a strong isospin violating contribution, where the decay width is proportional to the light quark mass difference squared, (md-mu)2. In addition this decay can be used to search for C-violating effects. The analysis is presented and the Dalitz plot parameters with statistical and systematical uncertainties are determined from a sample of 1.33·105 η→π+π-π0 events in the Dalitz plot. The asymmetry parameters with statistical uncertainties are presented which show no evidence of C-violation.

    Open access
  • Doktorsavhandling, monografi

    Thomé, Erik

    Multi-Strange and Charmed Antihyperon-Hyperon Physics for PANDA

    Abstract

    The prospects of studying multi-strange and charmed antihyperon-hyperon physics and CP violation in hyperon decays in the upcoming PANDA experiment at FAIR, Germany, have been studied in this thesis.

    The angular dependence on polarisation parameters in the decay of the spin 3/2 Omega hyperon was calculated using the density matrix formalism. Expressions for the angular distributions in the Ω -> ΛK and the subsequent Λ -> pπ decays were derived.

    Simulations were performed for the pbar p -> Ξ+ Ξ-, pbar p -> Ω+Ω- and pbar p -> Λc-Λc+ reactions. Special attention was given to the reconstruction of spin variables. It is shown that PANDA will register tens of events per second for the pbar p -> Ξ+Ξ- reaction. This should be compared to the previously existing data of a handfull of events. For the other two reactions the event rates will be lower, but still reasonably high. This will be the first measurements of these reactions. It is shown that spin variables can be reconstructed in all three reactions for all production angles of the hyperons. Simulations concerning the possibility to measure CP violation parameters in hyperon decays were also made for the reactions pbar p- > Λbar Λ and pbar p -> Ξ+Ξ-. It was found that false signals from detector asymmetries disappears if no particle identification criterium is used and the analysis is restricted to events were the hyperon decays occur close to the beam axis.

    The effect of the magnetic field in the PANDA detector on the measurement of hyperon spin variables was investigated for the case of pbar p -> Λbar Λ. The effect was observed to be small for polarisation and negligible for spin correlations.

    Open access
  • Doktorsavhandling, sammanläggning

    Söderström, Pär-Anders

    Collective Structure of Neutron-Rich Rare-Earth Nuclei and Development of Instrumentation for Gamma-Ray Spectroscopy

    Abstract

    Neutron-rich rare-earth nuclei are among the most collective nuclei that can be found in nature. In particular, the doubly mid-shell nucleus 170Dy is expected to be the nucleus where the collective structure is maximized. This has implications for the astrophysical r-process, since it has been suggested that the collectivity maximum plays an important role in the abundances of the rare-earth elements that are created in supernova explosions. In this work, the collective structure of the five nuclei 168,170Dy and 167,168,169Ho are studied and different theoretical models are used to interpret the evolution of collectivity around the mid-shell. In order to produce and study even more neutron-rich nuclei in this mass region, new radioactive ion beam facilities will be a valuable tool. These facilities, however, require advanced instruments to study the weak signals of exotic nuclei in a high background environment. Two of these instruments are the γ-ray tracking spectrometer AGATA and the neutron detector array NEDA. For AGATA to work satisfactorily, the interaction position of the gamma rays must be determined with an accuracy of at least five millimetres. The position resolution is measured in this work using a model independent method based on the Doppler correction capabilities of the detector at two different distances between the detector and the source. For NEDA, one of the critical parameters is its ability to discriminate between neutrons and γ rays. By using digital electronics it is possible to employ advanced and efficient algorithms for pulse-shape discrimination. In this work, digital versions of the common analogue methods are shownto give as good, or better, results compared to the ones obtained using analogue electronics. Another method which effectively distinguishes between neutrons and γ rays is based on artificial neural networks. This method is also investigated in this work and is shown to yield even better results.

    Open access
  • Doktorsavhandling, monografi

    Rathsman, Karin

    Modeling of Electron Cooling: Theory, Data and Applications

    Abstract

    The Vlasov technique is used to model the electron cooling force. Limitations of the applicability of the method is obtained by considering the perturbations of the electron plasma. Analytical expressions of the electron cooling force, valid beyond the Coulomb logarithm approximation, are derived and compared to numerical calculations using adaptive Monte Carlo integration. The calculated longitudinal cooling force is verified with measurements in CELSIUS.

    Transverse damping rates of betatron oscillations for a nonlinear cooling force is explored. Experimental data of the transverse monochromatic instability is used to determine the rms angular spread due to solenoid field imperfections in CELSIUS. The result, θrms= 0.16 ± 0.02 mrad, is in agreement with the longitudinal cooling force measurements. This verifies the internal consistency of the model and shows that the transverse and longitudinal cooling force components have different velocity dependences. Simulations of electron cooling with applications to HESR show that the momentum reso- lution ∆p/p smaller than 10−5 is feasible, as needed for the charmonium spectroscopy in the experimental program of PANDA. By deflecting the electron beam angle to make use of the monochromatic instability, a reasonable overlap between the circulating antiproton beam and the internal target can be maintained. The simulations also indicate that the cooling time is considerably shorter than expected.

    Open access
  • Doktorsavhandling, monografi

    Keleta, Samson

    Double Pion Production in the dd to αππ reaction

    Abstract

    The reaction dd → 4Heππ has been measured exclusively for the first time. The measurements were performed at Td = 712 MeV and Td = 1029 MeV, with the WASA detector assembly at CELSIUS (Uppsala-Sweden). The aim was to investigate a long standing puzzle, the so called ABC effect. This is a peculiar feature of double pion production in light nuclei collisions. In addition to confirming previous experimental observations in this regard, our results also reveal a strong angular dependence of the pions in the overall center of mass system as well as non-isotropic angular distribution of the low mass enhancement in the ππ invariant mass. The results are qualitatively reproduced by a theoretical model, according to which, the ABC effect is described as a result of kinematical enhancement in the independent production of the pion pairs from two parallel and independent NN → dπ reactions.

  • Licentiatavhandling, monografi

    Grape, Sophie

    PWO Crystal Measurements and Simulation Studies of Anti-Hyperon Polarisation for PANDA

    Abstract

    The Gesellschaft für Schwerionenforschung (GSI) facility in Darmstadt, Germany, will be upgraded to accommodate a new generation of physics experiments. The future accelerator facility will be called FAIR and one of the experimentsat the site will be PANDA, which aims at performing hadron physics investigations by colliding anti-protons with protons. The licentiate thesis consistsof three sections related to PANDA. The first contains energy resolutionstudies of PbWO4 crystals, the second light yield uniformity studies of PbWO4 crystals and the third reconstruction of the lambda-bar-polarisation in the PANDA experiment.

    Two measurements of the energy resolution were performed at MAX-Lab in Lund, Sweden, with an array of 3x3 PbWO4 crystals using a tagged photon beam with energies between 19 and 56 MeV. For the April measurement, the crystals were cooled down to -15 degrees C and for the September measurement down to -25 degrees C. The measured relative energy resolution, /E, is decreasing from approximately 12% at 20 MeV to 7% at 55 MeV. In the standard energy resolution expression /E = a/ b/E c, the three parameters a, b and c seem to be strongly correlated and thus difficult to determine independently over this relative small energy range. The value of a was therefore fixed to that one would expect from Poisson statistics of the light collection yield (50 phe/MeV) and the results from fits were /E=0.45%/ 0.18%/EGeV 8.63% and /E = 0.45%/0.21%/EGeV 6.12% for the April and September measurements, respectively. The data from the September measurement was also combined with previous data from MAMI for higher energies, ranging from approximately 64 to 715 MeV. The global fit over the whole range of energies gave an energy resolution expression of /E = 1.6%/ 0.095%/EGeV 2.1%.

    Light yield uniformity studies of five PbWO4 crystals, three tapered and two non-tapered ones, have also been performed. The tapered crystals delivered a light output which increased with increasing distance from the Photo Multiplier Tube (PM tube). Black tape was put on different sides of one tapered crystals, far from the PM tube to try to get a more constant uniformity prole. It was seen that the light output profile depends on the position of the tape. Generally, the steep increase in light output at large distances from the PM tube could be damped.

    The third part of the thesis concerns the reconstruction of the lambdabar polarisation in the reaction . Events were generated using a modied generator from the PS185 experiment at LEAR. With a 100% polarisation perpendicular to the scattering plane, a polarisation of (99±1.8)% was reconstructed. Slight non-zero polarisations along the axis determined by the outgoing hyperon as well as the axis in the scattering plane, were also reconstructed. These were (4.1±2.1)% and (2.6±2.0)% respectively. From this investigation it was shown that the detector efficiency was not homogeneous and that slow pions are difficult to reconstruct.

    Open access
  • Doktorsavhandling, monografi

    Davour, Anna

    Search for low mass WIMPs with the AMANDA neutrino telescope

    Abstract

    Recent measurements show that dark matter makes up at least one fifth of the total energy density of the Universe. The nature of the dark matter is one of the biggest mysteries in current particle physics and cosmology.

    Big Bang nucleosynthesis limits the amount of baryonic matter that can exist, and shows that the dark matter has to be non-baryonic. Particle physics provides some candidates for non-baryonic matter that could solve the dark-matter problem, weakly interacting massive

    particles (WIMPs) being the most popular. If these particles were created in the early Universe a substatial relic abundance would exist today. WIMPs in our galactic halo could be gravitationally bound in the Solar System and accumulate inside heavy bodies like the Earth. Supersymmetric extensions to the Standard Model give a viable WIMP dark matter candidate in the form of the lightest neutralino. This thesis describes an indirect search for WIMPs by the neutrino signature from neutralino annihilation at the core of the Earth using the AMANDA detector. As opposed to previous dark matter searches with AMANDA, this work focuses on the hypothesis of a relatively light WIMP particle with mass of 50-250GeV/c2

    The AMANDA neutrino telescope is an array of photomultiplier tubes installed in the clear glacier ice at the South Pole which is used as Cherenkov medium. Data taken with AMANDA during the period 2001-2003 is analyzed. The energy threshold of the detector is lowered by the use of a local correlation trigger, and the analysis is taylored to select vertically upgoing low energy events. No excess above the expected atmospheric neutrino background is found. New limits on the flux of muons from WIMP annihilations in the center of the Earth are calculated.

    Open access
  • Doktorsavhandling, sammanläggning

    Lundborg, Agnes

    The Charm of Excited Glue: Charmonium in e+e and ppbar collisions

    Abstract

    This thesis treats the mass range of charmonium states and excited gluonic fields in two experiments, BESII and PANDA, and outlines a phenomenological model that connects them.

    In BESII, e+e form a charmonium initial state, which is utilised as a source for secondary particles. The analysed channels, ψ´→ γK+K and ψ´→ γπ+π, give access to intermediate scalar states such as the two glueball candidates: f0(1500) and f0(1710). The f0(1710) is indeed observed in decay into both π+π and K+K and the f0(1500) is accepted as a necessary part of the π+π signal at the moderate 5% level. In addition, we observe the two tensor states f2(1270) (in both channels) and f2´(1525) (in K+K), but the need for the f2´(1525) is not firmly established. The region around 2 GeV/c2 is fitted with an f4(2050) and an f0(2200) in π+π. This region is fairly flat in K+K with a slight peak at the f0(2200). Branching ratios for all eight channels are given. A fit to the angular distribution of ψ´→ γ f2(1270) → γ π+πgave two possible solutions for the relative importance of helicity projections zero, one and two.

    The future ppbar experiment PANDA is still in the development phase; important physics goals have been defined and we are now taking on the laborious task of constructing a detector that is able to fulfil them. A simulation investigation of a theoretically preferred JPC=1–+ charmonium hybrid (Hc) is presented: ppbarHcπ0/η, Hcχc1 (π0π0)S–wave, χc1J/ψπ0, with a final state of seven photons and a lepton pair. To detect this channel next to full coverage of CM phase space is needed and as little material as possible before the electromagnetic calorimeter.

    A second simulation study of ppbar → ηcγγ at PANDA, suggests that the channel should be possible to detect with a signal-to-background ratio of 5±1 and a detection efficiency of at least 10%.

    By assuming a constant matrix element we obtain a relation between the decay width for ψppbar+m, which has been measured at BES for several cases, and the cross section for ppbar charmonium production in association with the same light meson, m (at for example PANDA). Cross sections of ~300–3000 pb were predicted for J/ψ production and ~30 pb for ψ' production. Isoscalars seem to be preferred to isovectors in J/ψ production, this might however be an artefact of simplifications within the model. A comparison with the only measured cross section, ppbar → J/ψπ0, suggests that the model is useful as a first estimate.

    Open access
  • Doktorsavhandling, monografi

    Robelius, Fredrik

    Giant Oil Fields - The Highway to Oil: Giant Oil Fields and their Importance for Future Oil Production

    Abstract

    Since the 1950s, oil has been the dominant source of energy in the world. The cheap supply of oil has been the engine for economic growth in the western world. Since future oil demand is expected to increase, the question to what extent future production will be available is important.

    The belief in a soon peak production of oil is fueled by increasing oil prices. However, the reliability of the oil price as a single parameter can be questioned, as earlier times of high prices have occurred without having anything to do with a lack of oil. Instead, giant oil fields, the largest oil fields in the world, can be used as a parameter.

    A giant oil field contains at least 500 million barrels of recoverable oil. Only 507, or 1 % of the total number of fields, are giants. Their contribution is striking: over 60 % of the 2005 production and about 65 % of the global ultimate recoverable reserve (URR).

    However, giant fields are something of the past since a majority of the largest giant fields are over 50 years old and the discovery trend of less giant fields with smaller volumes is clear. A large number of the largest giant fields are found in the countries surrounding the Persian Gulf.

    The domination of giant fields in global oil production confirms a concept where they govern future production. A model, based on past annual production and URR, has been developed to forecast future production from giant fields. The results, in combination with forecasts on new field developments, heavy oil and oil sand, are used to predict future oil production.

    In all scenarios, peak oil occurs at about the same time as the giant fields peak. The worst-case scenario sees a peak in 2008 and the best-case scenario, following a 1.4 % demand growth, peaks in 2018.

    Open access
  • Doktorsavhandling, sammanläggning

    Nordhage, Örjan

    On a Hydrogen Pellet Target for Antiproton Physics with PANDA

    Abstract

    The PANDA experiment is a part of the future FAIR accelerator facility and will study the strong interaction by detecting the reaction products from antiproton-proton annihilations in a near full solid-angle configuration. One option for the internal proton target in PANDA is frozen micro-spheres of hydrogen, so-called pellets.

    Such a pellet target is interesting because of the unique characteristics it offers; the high target thickness, the small interaction volume, the minimal gas load on the vacuum system, and the possibility of tracking individual pellets. Nevertheless, it is possible to allocate the bulky equipment needed to produce the pellets at a few meters away from the beam. This way particle detectors can be located close and almost fully around the interaction point.

    This thesis is devoted to the optimization of a pellet target. To perform measurements, a Pellet-Test Station was built at The Svedberg Laboratory, Uppsala. For the first time, experimental results show the pellet distribution in space and time, and in addition, the vacuum along the pellet pipes. Furthermore, dedicated measurements carried out at CELSIUS/WASA demonstrate the existence of pellet heating as a result of beam-target interactions.

    In performing calculations, the potential problems with pellet heating at PANDA are outlined. Moreover, to look at the consequences for the desired physics, a reaction involving short-lived D-mesons has been used to show the advantages of pellets compared to a more spacious target.

    In conclusion, these studies lead to a deeper understanding of the pellet properties, which makes it possible to suggest future improvements, such as cooling with no vibrations.

    Open access
  • Doktorsavhandling, sammanläggning

    Dahlfors, Marcus

    Studies of Accelerator-Driven Systems for Transmutation of Nuclear Waste

    Abstract

    Accelerator-driven systems for transmutation of nuclear waste have been suggested as a means for dealing with spent fuel components that pose potential radiological hazard for long periods of time. While not entirely removing the need for underground waste repositories, this nuclear waste incineration technology provides a viable method for reducing both waste volumes and storage times. Potentially, the time spans could be diminished from hundreds of thousand years to merely 1.000 years or even less. A central aspect for accelerator-driven systems design is the prediction of safety parameters and fuel economy. The simulations performed rely heavily on nuclear data and especially on the precision of the neutron cross section representations of essential nuclides over a wide energy range, from the thermal to the fast energy regime. In combination with a more demanding neutron flux distribution as compared with ordinary light-water reactors, the expanded nuclear data energy regime makes exploration of the cross section sensitivity for simulations of accelerator-driven systems a necessity. This fact was observed throughout the work and a significant portion of the study is devoted to investigations of nuclear data related effects. The computer code package EA-MC, based on 3-D Monte Carlo techniques, is the main computational tool employed for the analyses presented. Directly related to the development of the code is the extensive IAEA ADS Benchmark 3.2, and an account of the results of the benchmark exercises as implemented with EA-MC is given. CERN's Energy Amplifier prototype is studied from the perspectives of neutron source types, nuclear data sensitivity and transmutation. The commissioning of the n_TOF experiment, which is a neutron cross section measurement project at CERN, is also described.

    Open access
  • Doktorsavhandling, sammanläggning

    Matsson, Ingvar

    Studies of Nuclear Fuel Performance Using On-site Gamma-ray Spectroscopy and In-pile Measurements

    Abstract

    Presently there is a clear trend of increasing demands on in-pile performance of nuclear fuel. Higher target burnups, part length rods and various fuel additives are some examples of this trend. Together with an increasing demand from the public for even safer nuclear power utilisation, this implies an increased focus on various experimental, preferably non-destructive, methods to characterise the fuel.

    This thesis focuses on the development and experimental evaluation of such methods. In its first part, the thesis presents a method based on gamma-ray spectroscopy with germanium detectors that have been used at various power reactors in Europe. The aim with these measurements is to provide information about the thermal power distribution within fuel assemblies in order to validate core physics production codes. The early closure of the Barsebäck 1 BWR offered a unique opportunity to perform such validations before complete depletion of burnable absorbers in Gd-rods had taken place. To facilitate the measurements, a completely submersible measuring system, LOKET, was developed allowing for convenient in-pool measurements to be performed.

    In its second part, the thesis describes methods that utilise in-pile measurements. These methods have been used in the Halden test-reactor for determination of fission gas release, pellet-cladding interaction studies and fuel development studies.

    Apart from the power measurements, the LOKET device has been used for fission gas release (FGR) measurements on single fuel rods. The significant reduction in fission gas release in the modern fuel designs, in comparison with older designs, has been demonstrated in a series of experiments. A FGR database covering a wide range of burnup, power histories and fuel designs has been compiled and used for fuel performance analysis. The fission gas release has been measured on fuel rods with average burnups well above 60 MWd/kgU. The comparison between core physics calculations (PHOENIX-4/POLCA-7) and the in-pool measurements of thermal power indicates that the nodal power can generally be predicted with an accuracy within 4% and the bundle power with an accuracy better than 2%, expressed as rms errors.

    In-pile experiments have successfully simulated the conditions that occur in a fuel rod following a primary debris failure, being secondary fuel degradation. It was concluded that massive hydrogen pick-up takes place during the first few days following the primary failure and that a pre-oxidized layer does not function as a barrier towards hydriding in an environment with a very high partial pressure of hydrogen. Another series of in-pile experiments clearly indicate that increased UO2 grain size is an effective way of suppressing fission gas release in LWR fuel up to the burnup level covered (55 MWd/kgUO2).

    Open access
  • Doktorsavhandling, sammanläggning

    Willman, Christofer

    Applications of Gamma Ray Spectroscopy of Spent Nuclear Fuel for Safeguards and Encapsulation

    Abstract

    Nuclear energy is currently one of the world’s main sources of electricity. Closely connected to the use of nuclear energy are important issues such as the nonproliferation of fissile material that may potentially used in nuclear weapons (safeguards), and the management of the highly radioactive nuclear waste. This thesis addresses both these issues by contributing to the development of new experimental methods for ensuring safe and secure handling of the waste, with focus on methods to be used prior to encapsulation and final storage.

    The methods rely on high resolution gamma ray spectroscopy (HRGS), involving the measurement and analysis of emitted gamma radiation from the fission products 137Cs, 134Cs and 154Eu. This technique is nondestructive, making it relatively nonintrusive with respect to the normal operation of the nuclear facilities.

    For the safeguards issue, it is important to experimentally verify the presence and identity of nuclear fuel assemblies and also that the fuel has experienced normal, civilian reactor operation. It has been shown in this thesis that the HRGS method may be used for verifying operator declared fuel parameters such as burnup, cooling time and irradiation history. In the experimental part of the work, the burnup and the cooling time has been determined with an accuracy of 1.6% and 1.5%, respectively (1 σ).

    A technique has also been demonstrated, utilizing the ratio 134Cs/154Eu, with which it is possible to determine whether a fuel assembly is of MOX or LEU type. This is of interest for safeguards as well as for the safe operation of a final storage facility.

    As an improvement to the HRGS technique, measuring a part of the fuel assembly length in order to reduce measurement time has been suggested and investigated. A theoretical case for partial defect verification has also been studied as an extension of the HRGS technique.

    Finally, HRGS has been used for determining the decay heat in spent nuclear fuel assemblies, which is of importance for the safe operation of a final storage facility. This application is based on the radiation from 137Cs, and the accuracy demonstrated was within 3% (1 σ).

    Open access
  • Doktorsavhandling, sammanläggning

    Gollub, Nils

    Top-Quark and Charged Higgs Boson Production at Hadron Colliders: Data Analysis at the DØ Experiment and Simulations for the ATLAS Detector

    Abstract

    This thesis treats two different projects, both aiming at experimental tests at hadron colliders of some specific predictions of the Standard Model (SM) of particle physics and of its Minimal Supersymmetric extension (MSSM). The thesis is based on four papers.

    Papers I-III study the discovery potential for a heavy charged Higgs boson of the ATLAS experiment at the Large Hadron Collider (LHC). Charged Higgs bosons are part of the Higgs sector in many extensions to the SM and their detection would be an unambiguous sign of new physics.

    If the charged Higgs boson is heavier than the top quark, its dominant decay mode is into a top and a bottom quark. Searches in this decay channel at ATLAS are difficult mainly due to the large top-quark pair-production background. The possible gain obtained when requiring 4 b-tagged jets for the signal events is studied, but no significant improvement compared to an analysis requiring 3 b-tagged jets is found.

    If the masses of supersymmetric particles are sufficiently small, heavy charged Higgs bosons can decay into a chargino-neutralino pair. We show that in this decay channel charged Higgs bosons can be detected, given a favourable choice of parameters governing the MSSM.

    In a large-mass-splitting MSSM scenario, the charged Higgs decay into a W boson and a neutral Higgs can have a large branching fraction. We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large, irreducible SM background.

    Paper IV describes a measurement of the top-quark pair production cross-section performed with the DØ detector at the Tevatron collider. Signal events in the muon+jets decay channel are selected using topological event characteristics and a preliminary result of σ(ttbar)=3.8 +1.1-1.1(stat) +0.9-0.8(syst) +0.3-0.2(lumi) pb is obtained using an integrated luminosity of 363/pb.

    Open access
  • Doktorsavhandling, sammanläggning

    Alwall, Johan

    Quark Distributions and Charged Higgs Boson Production: Studies of Proton Structure and New Physics

    Abstract

    The Standard Model describes all elementary particles known today, but at larger energies it will have to be complemented with new particles and interactions. To be able to distinguish new physics at proton colliders such as LHC at CERN, it is essential to have an appropriate description of the colliding protons and their interactions. The study of the proton is important also in itself, to get a better understanding of the non-perturbative aspects of the strong interaction.

    In paper I-IV of this thesis, a model for the non-perturbative dynamics of quarks and gluons is developed, based on quantum fluctuations in hadrons. The parton distributions of the proton are given by momentum fluctuations, with sea quark distributions generated by fluctuations into baryon-meson pairs. This model can reproduce proton structure function data, as well as measured asymmetries between up and down valence quark distributions and between the anti-up and anti-down sea. It provides an intrinsic charm quark component as indicated by data. It also predicts an asymmetry in the strange sea of the proton, which can explain the NuTeV anomaly first attributed to new physics beyond the Standard Model.

    Charged Higgs bosons are predicted by several theories for new physics, including Supersymmetry. At proton colliders, the predicted dominant production mechanism is in association with top and bottom quarks. In paper V-VII, different contributions to this production are studied, and an algorithm is developed for combining the two dominant processes gb -> tH+/- and gg -> tbH+/-. The algorithm gives a smooth transition from small to large transverse momenta of the b-quark, which is important when the b-quark is observed. It also gives arguments for the choice of factorisation scale in the process.

    Open access
  • Doktorsavhandling, sammanläggning

    Ljungvall, Joa

    Characterisation of the Neutron Wall and of Neutron Interactions in Germanium-Detector Systems

    Abstract

    A Monte Carlo simulation of the Neutron Wall detector system has been performed using Geant4, in order to define optimum conditions for the detection and identification of multiple neutrons. Emphasis was put on studying the scattering of neutrons between different detectors, which is the main source of the apparent increase of the number of detected neutrons. The simulation has been compared with experimental data. The quality of neutron gated γ-ray spectra was improved for both two- and three-neutron evaporation channels. The influence of small amounts of γ rays mis-interpreted as neutrons was investigated. It was found that such γ rays dramatically reduce the quality of neutron gated γ-ray spectra.

    The interaction properties of fast neutrons in a closed-end coaxial and a planar high-purity germanium detector (HPGe) were studied. Digitised waveforms of HPGe preamplifier signals were recorded for time-of-flight separated neutrons and γ rays, emitted by a 252Cf source. The experimental waveforms from the detectors were compared to simulated pulse shapes. In the analysis, special emphasis was given to the detection of elastically scattered neutrons, which may be an important effect to take into account in future spectrometers based on γ-ray tracking. No differences between neutron and γ-ray induced pulse shapes were found in this work.

    A Monte Carlo simulation of the interactions of fast neutrons in the future 4π γ-ray spectrometer AGATA was also performed, in order to study the influence of neutrons on γ-ray tracking. It was shown that although there is a large probability of detecting neutrons in AGATA, the neutrons decrease the photo-peak efficiency of AGATA by only about 1% for each neutron emitted in coincidence with γ rays. The peak-to-background ratios in γ-ray spectra are, however, reduced to a much larger extent. The possibility of using AGATA as a neutron detector system was also investigated.

    Open access
  • Doktorsavhandling, sammanläggning

    Lantz, Mattias

    Investigations of Reaction Cross Sections for Protons and 3He

    Abstract

    The reaction cross section gives the probability that a particle will undergo a nonelastic process when passing through a nuclear medium. Therefore reaction cross section data are of importance both for theoretical studies and for applications in such diverse fields as medicine, biology, astrophysics and accelerator-driven transmutation of nuclear waste.

    There exist many data sets with angular distributions of elastic scattering, but very few measurements of the complementary reaction cross section have been performed. The measurement is in principle simple but has in practice proved to be very difficult to perform, and the relatively limited amount of experimental data displays some serious inconsistencies.

    Results from measurements of reaction cross sections are presented for:

    3He on 9Be, 12C, 16O, 28Si, 40Ca, 58,60Ni, 112,116,118,120,124Sn and 208Pb at 96, 138 and 167 MeV

    • protons on 12C, 40Ca, 90Zr and 208Pb at six energies in the energy range 80-180 MeV, and on

    58Ni at 81 MeV.

    Experimental uncertainties were 3-9% for 3He and 1.5-8% for protons.

    The apparatus and the experimental method used for the measurements of reaction cross sections, using a modified attenuation technique, is described. The detection method enables simultaneous measurements of reaction cross sections for five different sizes of the solid angles in steps from 99.0 to 99.8% of the total solid angle. The final results are obtained by extrapolation to the full solid angle.

    Experimental results are compared with predictions from optical model calculations using phenomenological global optical potentials.

    Phenomenological parametrizations of reaction cross sections for scattering of projectiles on targets are presented. The parametrizations show that reaction cross sections are very sensitive to matter distributions at very large radii of both the projectile and the target. For protons the derived relations makes it possible to predict the reaction cross sections on targets for which no experimental data exist.

    Open access
  • Doktorsavhandling, sammanläggning

    Hansen, Christian

    Neutrino Oscillations and Charged Higgs Bosons – Experimental Projects for Physics beyond the Standard Model

    Abstract

    This thesis is based on work done in two different experimental projects.

    The first project, the Tau RICH, is a previously proposed τ-neutrino appearance experiment for the CERN neutrino beam at the Gran Sasso laboratory in Italy. The proposed experimental concept is based on the use of focusing RICH detectors with liquid radiator (C6F14). Simulations made with a Geant4 code show that in the proposed experimental set-up, Cherenkov light from delta electrons will constitute a severe background that in practice would render the experiment unfeasible.

    The second project, ATLAS, is a general purpose detector at the CERN 14 TeV proton-proton collider LHC which will start operation in 2007. To make the reconstruction and selection of the events in ATLAS more accurate, complete and up-to-date information on the interaction of the produced particles with the detector is needed. A service program code, the Material Integration Service (MIS), has been developed which makes use of the detector descriptions already available in a Geant4 code and which uses a novel algorithm, based on line integrals evaluated within small volume elements that build up the detector. This code is demonstrated to constitute a practically useful tool of satisfactory performance and accuracy.

    The charged Higgs boson production in the gluon-bottom quark mode, gb → tH±, followed by charged Higgs decays into a chargino and a neutralino, is studied for a specific choice of values for the Minimal Supersymmetric Standard Model (MSSM) parameters. It is shown, using a Monte Carlo code to simulate the ATLAS detector and the assumed MSSM physics model, that for an integrated luminosity of 300 fb-1, in the intermediate region 4 < tanβ < 10 where H± decays to SM particles cannot be used for H± discovery, charged Higgs decays to non-SM particles can be used for Higgs discovery at the 5 σ significance level.

    Open access
  • Doktorsavhandling, sammanläggning

    Bergenwall, Bel E.

    From Particle-Production Cross Sections to KERMA and Absorbed Dose for the Case 96 MeV n-12C Interactions

    Abstract

    Neutron-carbon interactions have been studied with a focus on charged-particle production of relevance to radiation protection and medical applications, such as cancer therapy. The measurements have been performed using the particle-detection setup, MEDLEY, and the 96 MeV neutron beam at the The Svedberg Laboratory in Uppsala.

    Double-differential cross sections of inclusive charged-particle production are compared with recent calculations from models based on the GNASH code including direct, preequilibrium and compound processes. For protons, the shapes of the cross-section spectra are reasonably well described by the calculations. For the other particles- d, t, 3He and α- there are important discrepancies, in particular for 3He-ions and α-particles, concerning both shape and magnitude of the spectra.

    Using the new cross sections, partial as well as total KERMA coefficients have been determined. The coefficients have also been compared to previous experimental results and model calculations. The p, d and t KERMA coefficients are in good agreement with those from a previous measurement. For the helium isotopes, there are no previous measurements at this energy. The KERMA coefficients are considerably higher (by up to 30%) than those predicted by the calculations.

    The KERMA results indicate that protons and α -particles are the main contributors to the dose. A 6x6x6 cm3 carbon phantom, exposed to a broad and a pencil-like beam, is used for the computation of the absorbed doses deposited by these two particles in spheres of 1 μm in diameter, located at various positions in the phantom. The maximum doses are deposited at ~3 cm from the surface of neutron impact for protons and within 1 cm for α-particles. For the pencil beam, deposited doses are spread over regions of ~1.5 cm and ~300 μm transverse to the beam for protons and α-particles, respectively. The results are consistent with previous integral measurements at lower energies.

    Open access
  • Doktorsavhandling, sammanläggning

    Auce, Agris

    Reaction Cross Section Measurements for p,d,3He and 4He at Intermediate Energies

    Abstract

    Reaction cross sections were measured for protons at 65.5 MeV, for deuterons at 37.8, 65.5, 97.4 MeV, for 3He at 96.4, 137.8, 167.3 MeV, and for 4He at 69.6, 117.2, 163.9 and 192.4 MeV. Targets were 9Be, 12C, 16O, 28Si, 40,48Ca, 58,60Ni, 112,116,118,120,124Sn and 208Pb. 48Ca and 118Sn targets were used only for some of the measurements. Rest of the targets have been measured for all energies and projectiles but 4He at 69.6 MeV where reaction cross sections were measured for 9Be, 12C, 16O, 28Si, 40Ca targets. A modification of a standard attenuation technique was used. Details of the experimental design are presented.

    Experimental uncertainties were 2-3% for p, 3% for d and 3-10% for 3,4He.

    A strong forward peaking of the reaction products was observed for 3,4He. Therefore the standard reaction cross section measurement technique was not applicable for these projectiles. The forward peaking is also responsible for the increase of experimental uncertainties for these projectiles. The forward peaking of the reaction products is not known for other projectiles and has also not been observed with 3,4He at different - both higher and lower - energies. Possible explanations for this phenomenon are discussed.

    Optical model calculations of the reaction cross sections are in good agreement with the measured values.

    The measurements were performed with beams from the Gustav Werner cyclotron at the The Svedberg Laboratory, Uppsala.

    Open access
  • Doktorsavhandling, sammanläggning

    Stenmark, Mårten

    Shout at the eta

    Abstract

    Quantum chromodynamics has interesting limits both in the low and the high-energy region. In the low energy region one has phenomenology of meson interactions which are still not clearly understood. In the high-energy region one wants to find a new theory which will envelope gravity and the standard model in the quantum framework, possibly via some kind of string theory.

    In this thesis some aspects are touched upon including both these limits. On the one hand we look at meson scattering close to threshold and try to describe cross sections via phenomenological models such as the two-step model. We then go on and dwell upon noncommutative geometry, a framework which has been successful in describing certain aspects of the theory of strings.

    The low-energy calculations gave some insight into the need for finding better understanding of the theories of mesons. The work on noncommutative geometry was on the other hand fruitful in gaining understanding of certain connections between different star products and their relations on a local level.

    Open access
  • Doktorsavhandling, sammanläggning

    Jacobsson Svärd, Staffan

    A Tomographic Measurement Technique for Irradiated Nuclear Fuel Assemblies

    Abstract

    The fuel assemblies used at the Swedish nuclear power plants contain typically between 100 and 300 fuel rods. An experimental technique has been demanded for determining the relative activities of specific isotopes in individual fuel rods without dismantling the assemblies. The purpose is to validate production codes, which requires an experimental relative accuracy of <2 % (1 σ).

    Therefore, a new, non-destructive tomographic measurement technique for irradiated nuclear fuel assemblies has been developed. The technique includes two main steps: (1) the gamma-ray flux distribution around the assembly is recorded, and (2) the interior gamma-ray source distribution in the assembly is reconstructed. The use of detailed gamma-ray transport calculations in the reconstruction procedure enables accurate determination of the relative rod-by-rod source distribution.

    To investigate the accuracy achievable, laboratory equipment has been constructed, including a fuel model with a well-known distribution of 137Cs. Furthermore, an instrument has been constructed and built for in-pool measurements on irradiated fuel assemblies at nuclear power plants.

    Using the laboratory equipment, a relative accuracy of 1.2 % was obtained (1 σ). The measurements on irradiated fuel resulted in a repeatability of 0.8 %, showing the accuracy that can be achieved using this instrument. The agreement between rod-by-rod data obtained in calculations using the POLCA–7 production code and measured data was 3.1 % (1 σ).

    Additionally, there is a safeguards interest in the tomographic technique for verifying that no fissile material has been diverted from fuel assemblies, i.e. that no fuel rods have been removed or replaced. The applicability has been demonstrated in a measurement on a spent fuel assembly. Furthermore, detection of both the removal of a rod as well as the replacement with a non-active rod has been investigated in detail and quantitatively established using the laboratory equipment.

    Open access
  • Doktorsavhandling, monografi

    Koch, Inken

    Measurements of 2π0 and 3π0 Production in Proton-Proton Collisions at a Center of Mass Energy of 2.465 GeV

    Abstract

    Neutral two- and three-pion productions in proton-proton collisions at a center of mass energy of 2.465 GeV have been studied using the WASA detector and an internal pellet target at the CELSIUS storage ring in Uppsala. An important part of the detector for the measurments was a central electromagnetic calorimeter composed of 1012 CsI crystals, which measured the photons originating from neutral pion decays. Test measurements and calibration procedures for this detector part were carried out. An important part of the analysis was the identification of the neutral pions from the invariant mass of the decay gammas and the use of Monte Carlo simulations to understand the detector responds.

    Total cross sections for the pp→ppπ0π0 and pp→ppπ0π0π0 reactions are presented as well as distributions of relevant kinematical variables for the pp→ppπ0π0 reaction.

    The distributions show significant deviations from phase space predictions. These deviations are typical for resonance production. The excitation of two simultaneous Δ resonances seems to be the main reaction mechanism.

    Open access
  • Doktorsavhandling, monografi

    Jacewicz, Marek

    Measurement of the Reaction pp→ppπ+π-π0 with CELSIUS/WASA at 1.36 GeV

    Abstract

    A versatile detector setup prepared by the CELSIUS/WASA collaboration for exclusive studies of rare processes produced in proton and deuteron collisions with hydrogen and deuterium pellet targets is presented. For the near-threshold production of light mesons, π0 and η, the scattered beam and target particles are measured in the forward detector, while the products of the decaying mesons are registered in a central detector covering close-to-4π sr.

    The central detector is composed of a mini-drift chamber consisting of 1738 straw tubes for tracking of the charged particles and a plastic scintillator barrel consisting of 146 scintillation counters providing fast signals of the passing particles. These two detector parts are placed inside of a superconducting solenoid providing an axial magnetic field.

    Outside of the solenoid is placed an electromagnetic calorimeter consisting of 1012 CsI crystals. The construction, calibration and performance of the plastic scintillator barrel is presented in detail. Its main purpose is the discrimination of charged and neutral particles on the trigger level. It is also used for the identification of charged particles by ΔE-p (ΔE-E) technique in the off-line analysis.

    The mini-drift chamber is a detector for determination of particles momenta and reaction vertex. It is built with minimum structural material and designed to withstand high particle fluxes at a luminosity 1032cm-2s-1. The design of the mini-drift chamber, a description of the calibration procedure, its performance and integration in the data analysis are presented.

    The overall performance of the WASA detector is demonstrated by the analysis of the pp→ppπ+π-π0 reaction at 1.36 GeV incident proton energy. The total cross section for the non-resonant part of the reaction is estimated for the first time in this energy region to be 4.6 ±1.2 -0.9 +0.7 μb. The pp→ppη part of the total reaction cross section is estimated to be 4.8 μb which is consistent with the existing experimental information.

  • Doktorsavhandling, monografi

    Rouki, Chariklia

    Experimental Studies of the Synthesis and the Survival Probability of Transactinides

    Abstract

    In 1999 scientists in Dubna announced the successful synthesis of the nucleus 283112 by the reaction 48Ca+ 238U, with a cross-section of 5.0 pb. The isotope was found to decay by spontaneous fission (t1/2=81 s). Current nuclear theory, supported by the experimental data on 277112, 284112 and 285112, predicts significantly lower production cross-sections and α-emission as the predominant decay mode for isotopes of element 112. The reported properties of 283112 challenge theoretical predictions and raise questions on the subsequent syntheses of the nuclei 287114 and 291116. In order to confirm this discovery, the reaction was repeated under the same conditions, and events similar to the reported ones were searched for. During our first investigation, in 2001, we failed to observe any events to meet the criteria of the 1999 observation. Our second experiment is presented here. The current situation concerning isotope 283112 is discussed.

    The survival probability of fissionable heavy nuclei is described by the ratio n/f. The ratio can be directly evaluated from measurements of the neutrons emitted before and after fission from the excited compound nucleus and the fission fragments, respectively. An investigation on the survival probabilities of 264Rf and 263Rf against fission is described. The isotopes were produced by the reactions 26Mg+238U and 25Mg+238U and the angular distributions of the emitted neutrons were measured. The average Γnf ratios for the evaporation chains of the two isotopes were examined, and an attempt to evaluate the absolute ratio Γnf of the first-chance fission of 264Rf was made. The results of a similar earlier study on the isotopes 258No and 257No are also presented.

  • Doktorsavhandling, sammanläggning

    Edling, Fredrik

    DIXI – a Hybrid Pixel Detector for X-ray Imaging

    Abstract

    Medical X-ray imaging is an important tool in diagnostic radiology. The ionising-radiation dose to the patient is justified by the clinical benefit of the examination. Nonetheless, detectors that operate at even lower doses and provide more information to the radiologist are desired. A hybrid pixel detector has the potential to provide a leap in detector technology as it incorporates a more advanced signal-processing capability than currently used detectors.

    The DIXI digital detector is a hybrid pixel detector developed for X-ray imaging. It consists of a readout chip and a semiconductor sensor. The division in two parts makes it possible to optimise each part individually. The detector is divided into square pixels with a size of 270 x 270 μm2. DIXI has the ability to count single photons and every readout pixel has two embedded counters to allow the acquisition of two images close in time. A discriminator enables the selection of photons with energies above a preset threshold level.

    The readout chip Angie has been developed and its performance has been evaluated in terms of noise, threshold variation and capability to perform energy weighted counting. Silicon sensors have been fabricated, and a control system for DIXI has been designed and built. An electroless process for deposition of Ni/Au bumps on the chip and sensor has been optimised as a preparation for the assembly of a complete detector, which is being assembled by flip-chip bonding using anisotropic conductive film.

    A simulation library for the DIXI detector has been set up and results on the image quality are reported for different exposures and working conditions. A theoretical model for hybrid pixel detectors based on the cascaded linear system theory has been developed. The model can be used to investigate and optimise the detector for different detector configurations and operating conditions.

    Open access
  • Doktorsavhandling, sammanläggning

    del Risco Norrlid, Lilián

    Modeling the Performance of a Hybrid Pixel Detector for Digital X-ray Imaging

    Abstract

    The development of digital detectors for X-ray imaging in medical diagnostics receives an increasing amount of attention. The detector under development at the Department of Radiation Sciences at Uppsala University is a hybrid pixel detector, which consists of a semiconductor sensor mounted onto a readout chip. The readout chip is capable of performing photon counting and has an externally adjustable threshold.

    A simulation tool for the detector and a model applying the linear-systems transfer theory to X-ray hybrid pixel detectors have been developed. Also a characterization of the readout chip has been done. In order to estimate the potential of the detector for diagnostic radiology, we investigate the image quality using the spatial frequency dependent detective quantum efficiency (DQE). By means of the detector simulations, the influence of threshold setting, noise sources, level of exposure and charge sharing on the DQE have been studied. By means of the linear-systems theory, a single analytical expression is provided to obtain the DQE of a hybrid pixel detector.

    The method developed in this thesis will make it possible to optimize a detector design according to a particular medical application. It will also permit modifications and new features to be included without having to construct a full detector system.

    Open access
  • Doktorsavhandling, monografi

    Nadel-Turonski, Pawel

    Experimental Studies of Neutron Emission Induced by Heavy-Ion Scattering

    Abstract

    A beam of 250A MeV 17O ions was scattered from argon and xenon targets. The large excess of fast neutrons compared with statistical model calculations that was observed earlier for xenon, was confirmed and found for argon as well. Analysis and calculations show that a considerable fraction of these neutrons can be interpreted as coming from direct knock-out reactions.

    The angular distributions do not support the suggestion of using fast heavy ion scattering as a probe for the study of the neutron skin in nuclei. While the basic idea that a heavy projectile tends to sample the neutron wave function near the surface of the nucleus is sound, the measured neutron distribution is not as distinct as suggested by the previous experiment. This makes it difficult to distinguish direct reactions from other channels, such as semi-direct decay of giant resonances.

    The improvements in the experimental methods have made the concept of using the CELSIUS storage and cooler ring as an internal magnetic spectrometer attractive for other of experiments presently being prepared.

    Open access
  • Doktorsavhandling, sammanläggning

    Conrad, Jan

    A Search for Neutrinos from Cosmic Point Sources using AMANDA-B10 with Emphasis on Limit Calculation Techniques

    Abstract

    A search for cosmic point sources of neutrinos has been performed using data taken in 1999 with the AMANDA-B10 neutrino telescope.

    This work describes methods for signal and background separation and the statistical analysis of the final data sample. In particular, the multivariate method Support Vector Machines has been applied to achieve good background rejection while at the same time retaining high signal efficiency.

    A grid search covering the complete northern hemisphere revealed no statistical significant excess of events over the expected background from mis-reconstructed cosmic ray induced muons and muons induced by atmospheric neutrinos. Thus, no cosmic point sources of neutrinos have been detected. Upper limits on the neutrino flux for each cell of the grid are presented.

    Twenty potential sources of neutrinos chosen among three classes of astronomical objects (Blazars, Super Nova Remnants and Microquasars) have been preselected. Upper Limits on the flux of cosmic neutrinos from those are presented.

    The presence of systematic uncertainties makes the calculation of confidence limits an intricate problem. A method is presented which makes it possible to include these uncertainties into the frequentist construction of confidence intervals. Statistical properties of the presented method have been studied.

    Open access
  • Doktorsavhandling, sammanläggning

    Coadou, Yann

    Searches for the Charged Higgs at Hadron Colliders Based on the Tau Lepton Signature

    Abstract

    The Standard Model of particle physics has been very successful in predicting a wide range of phenomena and has so far been confirmed by all existing data to a very high precision.

    The work described in this thesis tests the limits of validity of the Standard Model (SM) in two areas believed to be sensitive to deviations from the theory: the observation of unpredicted particles and CP violation. The studies were performed within the framework of experiments at two hadron colliders, the future ATLAS detector scheduled for operation in 2007 at the Large Hadron Collider in Geneva and the currently running DØ experiment at the Tevatron in Chicago.

    The tau lepton’s distinctive signature is a useful tool in many new physics searches where it is present in the final state. As a first study in ATLAS a Monte Carlo analysis of two-tau final states, which are sensitive to the underlying structure of supersymmetric models, was performed.

    Several extensions of the SM predict the existence of a charged Higgs boson.The major part of this thesis has consisted in using tau leptons to search for the charged Higgs in the context of the Minimal Supersymmetric extension of the SM (MSSM). Results from this thesis show that searches for the H± → τντ decay channel extend the charged Higgs discovery reach for the ATLAS experiment compared to previous studies of other channels: the charged Higgs can be observed for masses up to ~ 600 GeV for tanβ > 10. Its mass can be determined with an uncertainty of 1 to 2%, dominated by statistical errors. The tanβ parameter can be derived from the absolute rate of this decay to a precision around 6% for 20 < tan β < 50.

    By measuring precisely the unitarity triangle parameter sin2β the SM description of CP violation can be put to a test. As a separate study a Monte Carlo analysis was performed in ATLAS, which shows that the systematic uncertainty is half the attainable statistical uncertainty.

    As part of the effort to search for the charged Higgs in the DØ experiment a trigger algorithm for tau leptons was written, extensively tested and implemented in the experiment. Trigger strategies for events containing taus were designed. These trigger studies will be useful also for many other new physics searches at DØ.

    Open access
  • Doktorsavhandling, sammanläggning

    Enberg, Rikard

    Quantum chromodynamics and colour singlet exchange in high energy interactions

    Abstract

    Quantum chromodynamics (QCD) is the fundamental theory in elementary particle physics that describes the strong interaction in terms of exchanges of force-carrying, colour-charged particles known as gluons. Although well-established through experimental verifications, there are fundamental unsolved problems in the theory.

    In this thesis, some novel aspects of strong interaction dynamics are studied in the context of colour singlet exchange processes — interactions where complex systems of gluons with no net colour charge are exchanged. Both perturbative and non-perturbative QCD methods are used, as well as Monte Carlo computer simulations.

    Soft colour interactions in the final state of a high energy collision can lead to effective colour singlet exchange. Non-perturbative models for such interactions are shown to give a good description of diffractive production of W, Z, bb, J/ψ and jets in pp collisions at the Tevatron. Predictions are given for diffractive Higgs boson and prompt photon production at hadron colliders.

    Rapidity gaps between jets is a new phenomenon which is studied with an improved perturbative calculation of hard colour singlet exchange using the BFKL equation, taking into account previously neglected contributions and non-leading logarithmic corrections. Including also underlying soft rescattering effects, the complete model reproduces well data from the Tevatron.

    Diffractive vector meson production through hard colour singlet exchange in γp collisions is studied in the framework of the conformal invariant non-forward solution of the BFKL equation. Expressions for helicity-dependent amplitudes are derived, and the results show good agreement with data on J/ψ and ρ production from the ep collider HERA.

    These studies lead to a deeper knowledge of complex gluon dynamics, and therefore advance our understanding of QCD.

    X

    Open access
  • Doktorsavhandling, sammanläggning

    Eklund, Lars

    Performance and Radiation Hardness of the ATLAS/SCT Detector Module

    Abstract

    The ATLAS experiment is a general purpose experiment being constructed at the Large Hadron Collider (LHC) at CERN, Geneva. ATLAS is designed to exploit the full physics potential of LHC, in particular to study topics con- cerning the Higgs mechanism, Super-symmetry and CP violation. The cross sections for the processes under study are extremely small, requiring very high luminosity colliding beams. The SemiConductor Tracker (SCT) is an essential part of the Inner Detector tracking system of ATLAS. The active elements of the SCT is 4088 detector modules, tiled on four barrel cylinders and eighteen endcap disks. As a consequence of the high luminosity, the detector modules will operate in a harsh radiation environment. This the- sis describes work concerning radiation hardness, beam test performance and methods for production testing of detector modules. The radiation hardness studies have been focused on the electrical performance of the front-end ASIC and the detector module. The results have identifed features of the ASIC failing after irradiation and conrmed the good performance of the re-designed ASIC. The beam tests have been performed in the late prototyping and the pre-production phase, verifying the specied performance of the detector modules. Special effort have been made to evaluate the performance of irradiated detector modules. The assembly, quality assurance and characterisation of the detector modules will be done in the collaborating institutes. The thesis reports on methods developed for use during the production, to assess the electrical performance.

    Open access
  • Doktorsavhandling, sammanläggning

    Tîmneanu, Nicuşor

    The colour of gluon interactions: Studies of Quantum Chromodynamics in soft and hard processes

    Abstract

    Quantum Chromodynamics (QCD) is the theory of the strong interaction, one of the fundamental forces of nature. The interactions between quarks are mediated by gluons, which are the colour-charged gauge fields in QCD. Hard processes with a large momentum transfer can be calculated using perturbation theory, while soft processes with a small momentum transfer are poorly understood. In this thesis, various aspects of the gluon interactions are studied based on the interplay between hard and soft processes.

    Soft gluon exchanges do not affect the dynamics of a hard process, but can rearrange the colour topology, resulting in different final states. The soft colour interaction models employ this idea and give a good description of all diffractive hard scattering data observed in pp collisions (W, Z, dijets, bb, J/ψ). This thesis also presents predictions for diffractive Higgs and γγ production at present and future hadron colliders.

    Multiple gluon exchanges give rise to saturation effects in hadronic collisions at high energies. Implementing this idea in photon-photon collisions gives new insight into the quantum structure of the photon and its interactions at high energies. When combined with perturbative calculations for single gluon exchange, the obtained results are in good agreement with experimental data from e+e- colliders.

    Off-shell gluon distributions in the photon give another perspective on the photon structure and have been parameterized for the first time in this thesis. These are useful for calculating cross sections of processes where the effects of transverse momenta are crucial, for example heavy quark production in γp or γγ collisions.

    Quantization of gauge fields which have a richer gauge structure than the gluons in QCD, is studied using the powerful BRST quantization formalism. Thus, first-stage reducible theories, like topological Yang-Mills and spin-5/2 gauge fields, are successfully quantized in an irreducible way.

    Understanding gluon interactions and the interplay between soft and hard processes paves the way towards solving the longstanding problem of confinement in QCD.

    Open access
  • Doktorsavhandling, sammanläggning

    Jansson, Peter

    Studies of Nuclear Fuel by Means of Nuclear Spectroscopic Methods

    Abstract

    The increasing demand for characterization of nuclear fuel, both from an operator and authority point of view, motivates the development of new experimental and, preferable, non-destructive methods. In this thesis, some methods based on nuclear spectroscopic techniques are presented.

    Various parameters of irradiated fuel are shown to be determined with high accuracy and confidence by utilizing gamma-ray scanning, tomography and passive neutron assay.

    Specifically, fuel parameters relevant for a secure storage of spent nuclear fuel in a long-term repository, such as e.g. burnup and decay heat, are shown to be determined with adequate accuracy. The techniques developed are expected to be implemented in the planned encapsulation facility in Sweden.

    Also, a device for tomographic measurements of the spatial distribution of thermal power in nuclear fuel assemblies has been built, tested and evaluated. The device utilizes single photon emission computed tomography (SPECT) in order to reconstruct the gamma-ray source distribution within a fuel assembly. The device is expected to be an important tool for validating reactor core simulators regarding new fuel designs.

    For safeguards purposes, two experimental methods for verifying the integrity, i.e. the possible loss of fissile material from a nuclear fuel assembly, are presented. Verification of integrity is shown to be possible on an individual fuel rod level.

    Open access
  • Doktorsavhandling, sammanläggning

    Marciniewski, Pawel

    Fast Digital Trigger Systems for Experiments in High Energy Physics

    Abstract

    The data acquisition in high energy physics experiments is typically started by a pulse from a fast coincidence-based trigger system. It is essential that such a system can identify an event in a shortest possible time and with as good selectivity as possible. In order to meet these requirements, several new techniques and developments in the domain of signal discrimination and rapid hit-topology analysis are presented. Two digital rise-time compensation methods were developed to improve the time resolution of the comparatively slow signals from inorganic scintillators. Both methods utilize double threshold analog comparators and digital processing logic.

    A unique adaptive threshold discrimination method was developed to reject after-pulses. The method was found to give the best timing, the smallest dead time and a complete rejection of noise pulses without missing physically significant pulses. Algorithms for fast multiplicity calculations of clusters of hits in two-dimensional matrices, in strings and in planar detector configurations were evaluated.

    All techniques described in this thesis were implemented and verified in the trigger systems built for the experiments WASA (Wide Angle Shower Apparatus) at TSL, Uppsala, Sweden and the AMANDA (Antarctic Muon And Neutrino Detector Array) at the South Pole.

  • Doktorsavhandling, sammanläggning

    Tegenfeldt, Fredrik

    Charged kaon and proton production in B-hadron decays

    Abstract

    The production of charged kaons and protons in B-hadron decays has been measured in e+e- annihilations at centre-of-mass energies corresponding to the Z0 mass. In total 1.6 million hadronic Z0 decays were analysed, corresponding to about 690000 B-hadron decays. They were collected using the DELPHI detector at the LEP collider at CERN during 1994 and 1995.

    Events containing B-hadron decays were identified using special characteristics of the B-hadron decay topology. In particular, the long lifetime of the B-hadron leads to decay vertices significantly displaced relative the interaction point. These so called secondary vertices were reconstructed using a powerful micro vertex detector. In order to discriminate B-hadron decay products from fragmentation tracks, a method was used where the impact parameter measured by the vertex detector was employed as a discriminating variable. The tracks were thus divided into two classes, one compatible with the interaction point and the other compatible with a secondary vertex. An unfolding method was used to extract the true B-hadron decay tracks from the two classes. Charged kaons and protons were identified using the Ring Imaging CHerenkov (RICH) detector and corrected for misidentification using an efficiency matrix. The analysis resulted in charged kaon and proton spectra from B-hadron decays, including previously unmeasured momentum regions. Integrating the spectra yielded the following multiplicities

    n(B-hadronK±X) = 0.683±0.021(stat) ±0.017(syst)

    n(B-hadronp/ p¯X) = 0.127±0.013(stat) ±0.019(syst)

    where the proton multiplicity does not include Λ baryon decay products.

  • Doktorsavhandling, sammanläggning

    Ellert, Mattias

    Search for Charged Higgs Bosons in e+e Collisions

    Abstract

    Several extensions to the Standard Model predict the existence of charged Higgs bosons. This thesis describes the search for such a particle using the data collected by the DELPHI detector at the Large Electron Positron (LEP) collider at the European laboratory for particle physics (CERN) in Geneva, Switzerland.

    In e+e - collisions charged Higgs bosons are predicted to be produced in pairs via an intermediate photon or Z0 boson. In the two Higgs doublet model (2HDM) the production cross section for a pair of charged Higgs bosons depends only on the centre of mass energy of the collision and the mass of the charged Higgs boson.

    Higgs bosons decay to the heaviest particles kinematically allowed. For a charged Higgs boson with a mass that can be produced at the LEP collider this means either a cs quark pair or a τυt lepton pair. The branching ratio between these decay channels depends on the parameters of the model.

    No statistically significant signal compatible with a charged Higgs boson was found. Using the predicted production cross sections from the 2HDM the existence of a charged Higgs boson with a mass lower than 73.8 GeV/c2 has been excluded at 95% confidence level independently of the decay branching ratios of the charged Higgs boson.

    Open access
  • Doktorsavhandling, sammanläggning

    Damet, Jerome

    Physics and Detector Simulation Studies of B-Meson Decays in ATLAS

    Open access
  • Doktorsavhandling, monografi

    Johanson, Jan

    Two-pion production in proton-proton collisions near threshold

    Abstract

    Two-pion production reactions in proton-proton collisions have been studied using the PROMICE/WASA detector and an internal cluster gas-jet target at the CELSIUS storage ring in Uppsala. Three out of the four isospin-independent reaction channels have been measured at several energies in the intermediate and near threshold energy region. Important parts of the analysis include the identification of neutral pions from the invariant mass of the decay gammas, the identification of positive pions with the delayed pulse technique and the use of Monte Carlo simulations to understand the detector response. The total cross sections for the pp®ppπ+π-, the pp®ppπ0π0 and the pp®pnπ+π0 reactions are presented at beam energies ranging from 650 to 775 MeV.

    The production mechanism for two-pion production near threshold seems to be dominated by resonance production. The contribution from the non-resonant terms alone can not reproduce the total cross sections. In most models, two-pion production is governed by the δ and the N* resonances in either one or both of the participating nucleons.

    The N*(1440)®N(πp)T=0Swave transition has been suggested as the dominating production mechanism for two-pion production in proton-proton collisions. However, the total cross sections presented in this thesis show that other production mechanisms also must give large contributions.

    Open access
  • Doktorsavhandling, sammanläggning

    Veldhuizen, Elbert Jan van

    Development of the CHICSi multi detector system and experiments with its auxiliary systems

    Abstract

    Two new detector systems are described, including several new detector concepts. They areintended for use in heavy ion reaction experiments at the CELSIUS storage ring of the TheSvedberg Laboratory in Uppsala. In addition, results of experiments are presented, togetherwith theoretical calculations.

    The CHICSi multi detector system consists of around 1750 detectors, mounted in a barrellike structure. Integrated electronic circuits are used for handling the electronic signalsalready inside the ultra high vacuum scattering chamber. CHICSi will be used for detection ofintermediate mass fragments with a high solid angle coverage. This work describes thesimulations and development done in order to achieve the desired detection properties, as wellas measurements for understanding the response function of the system.

    An integrated δ-E silicon detector could make future experiments, like CHICSi, more compact and less vulnerable. A prototype of such a detector is presented. Measurementsindicate that most properties are better than for any now commercially available detector. Residues from heavy ion reactions carry important information about the reaction process.However, due to their large mass and low velocity, they are difficult to detect. A time-of-flight telescope was developed for this purpose, with which residues were detected in 25A -400A MeV 14N, 16O and 20Ne on Ar, Kr and Xe reactions. The obtained residue velocities and linear momentum transfers at high beam energy are higher than observed in similar reactions that lead to fission. The telescope response was measured and analyzed.

    Pion production experiments were performed. The special. ramping mode of the CELSlUSring was used to extract excitation functions for positive and negative pions. There isreasonable agreement with BUU and QMD calculations. The measurement did not reveal anysign of a δ-ball resonance, which was predicted by some theories.

  • Doktorsavhandling, sammanläggning

    Gårdestig, Anders

    As simple as ABC - the dd → α X reaction explained

    Abstract

    A model is presented for the dd → αππ reaction. It is based on two parallell and almost independent NN processes, where the final deutrons fuse to form the α particle. While underestimating the results at lower energies, the modelgives a good quantitative description of the α-particle momentum distributions throughout the 0.8 < Td < 1.9 GeV energy range. In particular it reproduces the remarkable peak structure (the ABC effect) that dominates the spectra at these energies. The predictions of deuteron vector and tensor analyzing powers are also in good agreement with data, both in frequency and magnitude of the oscillations.

    By considering two npdππ processes instead of NNdπ, the model is extended to four-pion production. With a simple parameterization of the npdππ amplitude, the high missing mass part of the dd → αX spectra at Td1.9 GeV could be fairly well reproduced.

    The model is also applied to dd → αγγ, using two npdγ processes. This reaction is important as background to the charge-symmetry-breaking reaction dd → απ0. The calculated two-photon contribution is of the same magnitude as a reported π0 signal, taking the experimental resolution into account. New experiments are needed in order to clarify the situation.

  • Doktorsavhandling, sammanläggning

    Axelsson, Anders

    Studies of collective excitations in rare earth nuclei

  • Licentiatavhandling, sammanläggning

    Studies of Nuclear fuel by means of Nuclear Spectroscopy Methods

    Jansson, Peter

    Abstract

    This paper which is a thesis for the title teknologie licentiat is a summary text of several works performed by the author regarding spectroscopic measurements on spent nuclear fuel. Methods for determining the decay heat of spent nuclear fuel by means of gammaray spectroscopy and for verifying the integrity of nuclear fuel by means of tomography is presented. A summary of work performed regarding gammaray detector technology for studies of fission gas release is presented.

    Open access
  • Licentiatavhandling, monografi

    A Tomographic method for Verification of the Integrity of Spent Nuclear Fuel

    Jacobsson, Staffan

  • Licentiatavhandling, monografi

    Tagging of Neutrons by Detecting Spectator Protons from Quasi-free Proton-Neutron Reactions on Deuterium

    Sundberg, Petter

  • Doktorsavhandling, sammanläggning

    Ruber, Roger

    An ultra-thin-walled superconducting solenoid for meson-decay physics

    Abstract

    A compact and extremely thin-walled superconducting warm-bore solenoid magnet, has been developed for the WASA detector setup at the CELSIUS accelerator and storage ring of the The Svedberg Laboratory. It provides a central axial magnetic field strength of 1.3 tesla, and can be operated in a persistent current mode during several weeks without a significant decline of the field strength. The overall wall thickness of the magnet is a record low 0.18 radiation lengths which is equivalent to 16 millimetres of aluminium.

    The WASA detector setup will be used for the measurement of inelastic protonnucleon reactions, in particular the production of light mesons and their subsequent decays. It is capable of identifying charged particles and photons over a solid angle close to 4π with a high measurement accuracy in energy and track coordinates. Some π0 and η rare decay processes that are accessible with the WASA detector setup can be used for probing the limits of the Standard Model. Accurate studies of such decays require a calorimeter for the energy measurement of photons and a magnet for the momentum measurement of charged particles. The thinwalled magnet is placed inside of the cylinder-shaped calorimeter and not outside, as it is traditionally done in comparable detector setups. Due to this arrangement, the calorimeter readout electronics do not have to operate in a magnetic field.

    The magnet design has been optimized for momentum measurements while the wall thickness was minimized in order to avoid electromagnetic showers and to maintain accurate energy measurements in the calorimeter. It is made as a split-coil solenoid with a central gap of 40 millimetres creating an opening for a tube guiding small frozen hydrogen pellets into the circulating beam. The coil is 9 millimetres thick with a length of 465 millimetres, a diameter of 554 millimetres and a mass of 20 kilograms. It has a glass-fiber support structure, a cryostat with 1 mm thick corrugated walls of aluminium and high-purity aluminium strips forimproved heat conduction. The cryostat has only one radiation shield and is cooled by a small helium refrigerator. A flexible diagnostics and control system has been developed. The calorimeter readout electronics are shielded from the magnetic field by an iron yoke.

  • Doktorsavhandling, sammanläggning

    Pomp, Stephan

    Hyperon polarisation in the reaction p¹²C

  • Doktorsavhandling, sammanläggning

    Gunther Axelsson, Maria

    Production asymmetry of strange quarks in electron-positron annihilation at LEP

    Abstract

    The forward-backward asymmetry in the production of strange quarks in electron-positron annihilation has been measured at a centre-of-mass energy corresponding to the mass of the Z0 particle. The asymmetry at this energy is highly sensitive to the ratio between the vector and axial-vector couplings of the quark to the Z0 and to the value of the electroweak mixing angle sin2 θw. Together with the previously measured value of the forward-backward asymmetry of the bottom quark, the measurement provides a test of the important theoretical prediction that the couplings to the Z0 are universal for all down-type quarks.

    The analysis is based on 1.4 million hadronic Z0 decays recorded in 1994 with the DELPHI detector system at the LEP collider at CERN. The strange quarks are selected using high-momentum charged kaons identified by the Ring Imaging CHerenkov (RICH) detectors. The charged kaon momentum is used to evaluate the probability for an event to belong to one of six possible event classes. Five classes are determined by the flavour of the primary quark (up, down, charm, strange and bottom) and the sixth class contains misidentified particles. The forward-backward asymmetry is determined using a maximum-likelihood method. At the Z0 pole, the asymmetry is found to be

    AFB0, s = 0.105 ± 0,016(stat.) ± 0.0006(syst.)

    which is the most precise measurement available for the strange quark asymmetry. The result is consistent with the previously measured value of the asymmetry of, the bottom quark, and thus with the predicted universality of the down-type quark couplings to the Z0. The obtained asymmetry corresponds to an electroweak mixing angle sin2 θw = 0.2229 ± 0.0030.

  • Doktorsavhandling, sammanläggning

    Edin, Anders

    Interplay between soft and hard processes in quantum chromodynamics

    Abstract

    In QCD, the theory of strong interactions, hard processes with large momentum transfers can be calculated using perturbation theory, while soft processes with small momentum transfers are poorly understood. In this thesis, phenomenological models of soft and hard QCD processes are developed and tested.

    A new model is presented for the distribution of quarks and gluons in hadrons. They are derived from a spherically symmetric, Gaussian, distribution of the quark and gluon momenta in the hadron rest frame. The proton structure function F2 is calculated from the model and evolved using next-to-leading order QCD, resulting in a successful comparison-with deep inelastic scattering data.

    A unified description is given of the hadronic final states observed in deep inelastic electron-proton scattering at HERA, regarding both the large forward energy flow and the rapidity gap events with no particles in a large forward angular region. The model is based on perturbative QCD complemented with a new "soft colour interaction" mechanism which affects the hadronic final state, and provides a continuous description of the transition from diffractive to non-diffractive hard scattering.

    The model for soft colour interactions also describes the surprisingly high production rate of heavy quarkonia observed in proton-antiproton collisions at the Tevatron.

  • Licentiatavhandling, monografi

    Nuclear Fuel Performance Studies Using High-Resolution Gamma-Ray Spectroscopy

    Matsson, Ingvar

  • Doktorsavhandling, sammanläggning

    Zubarev, Roman Alexandrovich

    Mass spectrometry of biopolymers based on ion-induced desorption

    Abstract

    Various aspects of biopolymer molecular characterization by their molecular masses havebeen studied, with emphasis on ion-induced desorption and time-of-flight mass Spectrometry(TOF MS). Limitations of the average-isotopic mass concept, as well as the utility ofaccurate monoisotopic mass measurements for deriving amino-acid and elementalcompositions, are discussed. A new sufficiency criterion of mass accuracy for peptidecharacterization is formulated. Experimentally achievable mass accuracy in TOF MS basedon MeV-ion induced desorption is studied. A new method of deriving peptide structuralinformation using partial acid hydrolysis and accurately measured hydrolysis fragmentmasses is developed.

    Secondary ion formation mechanisms in ion-induced desorption have been studiedusing keV and MeV atomic and polyatomic projectiles. In the MeV-atomic-ion mode, kineticenergies and formation times of secondary ions have been investigated. The results suggestdelayed (10-10-10-9s) formation of target-specific ions in the gas phase. A concept ofexothermic matrices has been tested experimentally. A new effective matrix for peptides andproteins, HMX, has been found. In the keV-atomic-ion mode, target-specific ions are foundto possess kinetic energy distributions that are characteristic for gas-phase ion formation. Thissuggests that the ion-formation mechanisms may be similar in both MeV and keV modes.Polyatomic ion-induced desorption has been studied using multiply-charged proteinprojectiles. The total negative ion yield is found to depend primarily on the surface density ofthe deposited energy. The utility of these findings for mass determination of mixturecomponents from complicated electrospray-ionization spectra is demonstrated.

  • Licentiatavhandling, monografi

    Electronic instrumentation for high energy physics.

    Marciniewski, Pavel

  • Licentiatavhandling, monografi

    Electronic instrumentation for multichannel scintillation detector systems.

    Zernov, Alexei

  • Licentiatavhandling, monografi

    Nuclear structure studies using coincidence measurements of particles and gamma rays

    Persson, Jan

  • Licentiatavhandling, monografi

    Design of a new Data Acquisition System incorporating the Asynchronous Transfer Mode (ATM) Protocol.

    Kobylecki, Klaudius

  • Licentiatavhandling, monografi

    Injection and electron cooling of ion beams in a storage ring

    Hedblom, Karin

  • Licentiatavhandling, monografi

    Stability of the doubly magic 100Sn core deduced from excited states in 99Cd51

    Lipoglavsek, Matej

  • Licentiatavhandling, monografi

    Detector System for Neutral Pion Production in Light Nuclei Collisions: Design and Initial Results

    Isaksson, Stefan