Hyperon electromagnetic form factors in the timelike region

Abstract

Electromagnetic form factors of hyperons ($\Lambda$, $\Sigma$, $\Xi$) in the timelike region, accessible in the reaction $e^{+}{e}^{-}\to \bar{Y}Y$, 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 $\bar{Y}Y$ system. This interaction is taken into account in the calculation, utilizing $\bar{Y}Y$ potential models that have been constructed by the Jülich group for the analysis of data from the reaction $\bar{p}p\to \bar{Y}Y$ 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.

Comments: 13 pages, 10 figures