Electromagnetic and Spin Properties of Hyperons

  • Date: –11:30
  • Location: Zoom
  • Lecturer: Elisabetta Perotti (Uppsala University)
  • Contact person: Rebeca Gonzalez Suarez
  • Seminarium

This will a virtual seminar, hosted in Zoom
Meeting ID: 683 3340 6891
Direct link: https://uu-se.zoom.us/j/68333406891

The study of hyperons improves our understanding of nature in multiple ways. The intrinsic properties of hadrons are not fully understood at a fundamental level. Hence, the electromagnetic properties of hyperons provide complementary information to that of the nucleon and therefore allow for a broader investigation of the structure of matter. Electromagnetic form factors  have been extensively studied for the nucleon, and are now addressed also in the hyperon sector. In particular, my thesis focuses on the determination of the electromagnetic Sigma-Lambda hyperon transition form factors at low energies. Subsequently this analysis has been extended to the decuplet spin-3/2 Sigma*-Lambda transition.  A pioneering framework that makes use of dispersion relations to combine theoretical and experimental input is presented. Assuming that these transition form factors are saturated by a two-pion inelasticity, their imaginary part can be written in terms of the pion vector form factor and a  pion-hyperon scattering amplitude. Chiral perturbation theory at next-to-leading order has been used to calculate the latter, while the pion vector form factor and the related pion phase-shift are known from measurements.

The spin properties of hyperons can be resolved through their weak decays. The angular distribution of their decay products displays both  polarization parameters and decay asymmetry parameters. These originate from processes characterized by an interplay of partial waves and are useful for different purposes.
On the one hand, the polarization is sensitive to the production mechanism. In the proton-antiproton case, it can be used to probe the strong interaction in the non-perturbative regime while in the electron-positron case it contains the relative phase between complex electromagnetic form factors. On the other hand, decay asymmetry parameters are used to construct observables that test CP violation.  Additional sources of CP violation must be found to solve the problem of the baryon asymmetry in our universe. My thesis provides a systematic method to retrieve both polarization and decay asymmetry parameters directly from the angular distribution of the hyperon decay products.