Observation of J=ψ Decays to e plus e - e plus e - and e plus e - μ plus μ -

Abstract

Using a data sample of 4.481 x 108 psi o3686 thorn events collected with the BESIII detector, we report the first observation of the four-lepton-decays J=psi -> e thorn e-e thorn e- and J=psi -> e thorn e-mu thorn mu- utilizing the process psi o3686 thorn -> pi thorn pi-J=psi. The branching fractions are determined to be 1/25.48 0.31ostat thorn 0.45osyst thorn x 10-5 and 1/23.53 0.22ostat thorn 0.13osyst thorn x 10-5, respectively. The results are consistent with theoretical predictions. No significant signal is observed for J=psi -> mu thorn mu-mu thorn mu-, and an upper limit on the branching fraction is set at 1.6 x 10-6 at the 90% confidence level. A CP asymmetry observable is constructed for the first two channels, which is measured to be o-0.012 0.054 0.010 thorn and o0.062 0.059 0.006 thorn , respectively. No evidence for CP violation is observed in this process