The electromagnetic form factors of the $\Lambda$ in the timelike region

Abstract

The reaction $e^+e^- \to \bar \Lambda \Lambda$ is investigated for energies close to the threshold. Specific emphasis is put on the role played by the interaction in the final $\bar \Lambda \Lambda$ system which is taken into account rigorously. For that interaction a variety of $\bar \Lambda \Lambda$ potential models is employed that have been constructed for the analysis of the reaction $\bar p p \to \bar \Lambda \Lambda$ in the past. The enhancement of the effective form factor for energies close to the $\bar \Lambda \Lambda$ threshold, seen in pertinent experiments, is reproduced. Predictions for the $\Lambda$ electromagnetic form factors $G_M$ and $G_E$ in the timelike region and for spin-dependent observables such as spin-correlation parameters are presented.