Hyperon electromagnetic form factors in the timelike region

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 Julich 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 $e^+e^- to bar Sigma^0Lambda$, is reproduced. With regard to the reactions $e^+e^- to bar Sigma^- Sigma^+, barSigma^0Sigma^0, barSigma^+Sigma^-$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $barSigmaSigma$ 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.