## Seminar on Theoretical Nuclear Physics

## 16.04.19 15:15

# Electromagnetic and weak transitions of hyperons

## Stefan Leupold (Uppsala University)

Abstract:

In the last decades a lot of progress has been made in the understanding of the electromagnetic form factors of the nucleons and transition form factors of the nucleon to baryonic resonances. This information can be complemented and deeper examined by determining the corresponding quantities for hyperons. Dalitz decays of hyperons into lighter hyperons and a lepton pair provide access to low-energy transition form factors. On the theory side one can use dispersion theory to relate these form factors to the pion vector form factor and pion-hyperon scattering amplitudes. The latter can be addressed with chiral perturbation theory including decuplet states (1, 2). Translating this formalism to nucleons (3), one can cross-check the results against a fully dispersive calculation (4).

To obtain a better understanding of neutrino-matter interaction it is interesting to examine the weak transition from the nucleon to the Delta decuplet state beyond the result from current algebra (5). In a chiral effective field theory of octet and decuplet baryons (2) the leading deviation from current algebra is encoded in one flavor symmetric low-energy constant. Being flavor symmetric, the very same low-energy constant appears also in three-body decays of decuplet hyperons to pions, photons and ground-state hyperons and in weak decays of the Omega baryon (6). Prospects to calculate and to measure these decays are discussed.

(1) C. Granados, S. Leupold and E. Perotti, The electromagnetic Sigma-to-Lambda hyperon transition form factors at low energies, Eur. Phys. J. A 54, 103 (2017).

(2) M. Holmberg and S. Leupold, The relativistic chiral Lagrangian for decuplet and octet baryons at next-to-leading order, Eur. Phys. J. A 43, 103 (2018)

(3) S. Leupold, The nucleon as a test case to calculate vector-isovector form factors at low energies, Eur. Phys. J. A 54, 1 (2018)

(4) M. Hoferichter, B. Kubis, J. Ruiz de Elvira, H.-W. Hammer and U.-G. Meißner, On the pi pi continuum in the nucleon form factors and the proton radius puzzle, Eur. Phys. J. A 53, 331 (2016)

(5) L. Alvarez-Ruso et al., NuSTEC White Paper: Status and challenges of neutrino-nucleus scattering, arXiv: 1706.03621 (hep-ph).

(6) M. Holmgren and Stefan Leupold, work in progress.

Bitte beachten:

Termin: Dienstag, 16.04., 15:15 Uhr

Ort: Hörsaal HISKP