Hyperon electromagnetic form factors in the timelike region

Electromagnetic form factors of hyperons ($Λ$, $Σ$, $Ξ$) 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 Jülich 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 $e^+e^- \to \bar ΛΛ$ and $e^+e^- \to \bar Σ^0Λ$, is reproduced. With regard to the reactions $e^+e^- \to \bar Σ^- Σ^+, \ \barΣ^0Σ^0, \ \barΣ^+Σ^-$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $\barΣΣ$ interaction. Predictions for the electromagnetic form factors $G_M$ and $G_E$ in the timelike region are presented for the $Λ$, $Σ$, and $Ξ$ hyperons.

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