Observation of J/ψ decays to e+e−e+e− and e+e−μ+μ−

Using a data sample of 4.481×108  ψ(3686) events collected with the BESIII detector, we report the first observation of the four-lepton-decays J/ψ→e+e−e+e− and J/ψ→e+e−μ+μ− utilizing the process ψ(3686)→π+π−J/ψ. The branching fractions are determined to be [5.48±0.31(stat)±0.45(syst)]×10−5 and [3.53±0.22(stat)±0.13(syst)]×10−5, respectively. The results are consistent with theoretical predictions. No significant signal is observed for J/ψ→μ+μ−μ+μ−, and an upper limit on the branching fraction is set at 1.6×10−6 at the 90% confidence level. A CP asymmetry observable is constructed for the first two channels, which is measured to be (−0.012±0.054±0.010) and (0.062±0.059±0.006), respectively. No evidence for CP violation is observed in this process. Published by the American Physical Society 2024