Hyperon electromagnetic form factors in the timelike region
J. Haidenbauer, Ulf-G. Meißner, L. Dai
Abstract
Electromagnetic form factors of hyperons ($\mathrm{\ensuremath{\Lambda}}$, $\mathrm{\ensuremath{\Sigma}}$, $\mathrm{\ensuremath{\Xi}}$) in the timelike region, accessible in the reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\overline{Y}Y$, 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 $\overline{Y}Y$ system. This interaction is taken into account in the calculation, utilizing $\overline{Y}Y$ potential models that have been constructed by the J\"ulich group for the analysis of data from the reaction $\overline{p}p\ensuremath{\rightarrow}\overline{Y}Y$ in the past. The enhancement of the effective form factor for energies close to the threshold, seen in experiments of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\overline{\mathrm{\ensuremath{\Lambda}}}\mathrm{\ensuremath{\Lambda}}$ and ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\overline{\mathrm{\ensuremath{\Sigma}}}}^{0}\mathrm{\ensuremath{\Lambda}}$, is reproduced. With regard to the reactions ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}{\mathrm{\ensuremath{\Sigma}}}^{+}$, ${\overline{\mathrm{\ensuremath{\Sigma}}}}^{0}{\mathrm{\ensuremath{\Sigma}}}^{0}$, ${\overline{\mathrm{\ensuremath{\Sigma}}}}^{+}{\mathrm{\ensuremath{\Sigma}}}^{\ensuremath{-}}$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $\overline{\mathrm{\ensuremath{\Sigma}}}\mathrm{\ensuremath{\Sigma}}$ interaction. Predictions for the electromagnetic form factors ${G}_{M}$ and ${G}_{E}$ in the timelike region are presented for the $\mathrm{\ensuremath{\Lambda}}$, $\mathrm{\ensuremath{\Sigma}}$, and $\mathrm{\ensuremath{\Xi}}$ hyperons.