Hyperon electromagnetic form factors in the timelike region

TL;DR

This paper models hyperon electromagnetic form factors in the timelike region near reaction thresholds, incorporating final state interactions, and provides predictions consistent with experimental enhancements and channel interplay.

Contribution

It introduces a calculation of hyperon form factors near thresholds using $ar YY$ potential models, accounting for final state interactions, and offers new predictions for various hyperons in the timelike region.

Findings

Reproduces experimental enhancement of form factors near thresholds.

Identifies interplay between different $ar ext{Sigma} ext{Sigma}$ channels at low energies.

Provides predictions for $G_M$ and $G_E$ form factors for hyperons.

Abstract

Electromagnetic form factors of hyperons ($\Lambda$, $\Sigma$, $\Xi$) in the timelike region, accessible in the reaction $e^+e^- \to \bar YY$, are studied. The focus is on energies close to the reaction thresholds, where the properties of these form factors are significantly influenced by the interaction in the final $\bar YY$ system. This interaction is taken into account in the calculation, utilizing $\bar YY$ potential models that have been constructed by the J\"ulich group for the analysis of data from the reaction $\bar pp \to \bar YY$ in the past. The enhancement of the effective form factor for energies close to the threshold, seen in experiments of $e^+e^- \to \bar \Lambda \Lambda$ and $e^+e^- \to \bar \Sigma^0\Lambda$, is reproduced. With regard to the reactions $e^+e^- \to \bar \Sigma^- \Sigma^+, \ \bar\Sigma^0\Sigma^0, \ \bar\Sigma^+\Sigma^-$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $\bar\Sigma\Sigma$ interaction. Predictions for the electromagnetic form factors $G_M$ and $G_E$ in the timelike region are presented for the $\Lambda$, $\Sigma$, and $\Xi$ hyperons.