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

## TL;DR

This paper uses dispersion theory and chiral perturbation theory to analyze the low-energy electromagnetic transition form factors between Sigma and Lambda hyperons, highlighting the importance of including decuplet baryons for accurate results.

## Contribution

It introduces a combined dispersion and chiral perturbation theory approach to compute hyperon transition form factors, emphasizing the necessity of decuplet baryons for realistic predictions.

## Key findings

- Electric transition form factor is very small at low energies.
- Magnetic transition form factor depends on a poorly known low-energy constant.
- Measurement of the magnetic transition radius can improve predictive accuracy.

## Abstract

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