Final PhD seminar: Glimpse of a Hyperon Transition

by Jana Rieger (Uppsala University)

Thursday 15 Jan 2026, 10:30 → 12:30 Europe/Stockholm

Beurlingrummet 10238 (Ångströmlaboratoriet)

This is the final seminar of Jana Rieger, as a preparation for her PhD defense on February 6th. The seminar will include a general discussion about her presentation and findings, while there will be a dedicated discussion session on January 29th where those who read Jana's PhD thesis will ask more detailed questions on the content.

 

Abstract: Hadron physics experiments enable us to obtain a better understanding of the strong force in the non-perturbative regime through, e.g., hadron structure studies. The location and motion of the building blocks of hadrons at the femtometer scale is quantified by electromagnetic form factors.
For stable hadrons such as protons, the space-like form factors are accessible in electron-hadron scattering experiments. However, for the short-lived hyperons, these scattering experiments are not feasible, calling for alternative approaches. In electromagnetic Dalitz decays of hyperons, the timelike structure can be described in terms of transition form factors. We study the only
electromagnetic transition between ground-state hyperons, the Σ° to Λ transition.
The FAIR Phase-0 experiment PANDA@HADES provides an excellent opportunity to measure Dalitz decays since it enables the reconstruction of the hadronic decay products of the hyperons, as well as the electron-positron pair from the Dalitz decay. I present an analysis procedure for selecting hyperon Dalitz decays with low-momentum leptons using the proton-proton data collected with a beam kinetic energy of T = 4.5 GeV by the HADES
experiment. Furthermore, I identify the dominant background sources, compare MC simulations and experimental data, and outline a roadmap for pioneering measurements of the branching ratio of the Σ° Dalitz decay and ultimately the magnetization radius of the Σ° to Λ transition.
On the path towards the measurement of the Σ° Dalitz decay, I have developed tools and methods to investigate and improve the data quality. The open-source software package KinFit provides kinematic-fitting tools for hadron-physics experiments. KinFit can be utilized to improve the resolution of the measured track parameters, exploiting kinematic and geometric
constraints. Moreover, I have performed a measurement of elastic proton-proton scattering. This made it possible to tune the experimental setup, to extract the integrated luminosity of the full proton-proton data sets at T = 4.5 GeV and T = 1.6 GeV, and to determine the differential cross sections.