Observation of $J/\psi$ decays to $e^{+}{e}^{-}{e}^{+}{e}^{-}$ and $e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$

Abstract

Using a data sample of $4.481\times 10^8{\psi }^{\prime }$ events collected with the BESIII detector, we report the first observation of the four-lepton-decays $J/\psi \to e^{+}{e}^{-}{e}^{+}{e}^{-}$ and $J/\psi \to e^{+}{e}^{-}{\mu }^{+}{\mu }^{-}$ utilizing the process ${\psi }^{\prime }\to {\pi }^{+}{\pi }^{-}J/\psi$. The branching fractions are determined to be $[5.48\pm 0.31(\mathrm{stat})\pm 0.45(\mathrm{syst})]\times 10^{-5}$ and $[3.53\pm 0.22(\mathrm{stat})\pm 0.13(\mathrm{syst})]\times 10^{-5}$, respectively. The results are consistent with theoretical predictions. No significant signal is observed for $J/\psi \to {\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$, and an upper limit on the branching fraction is set at $1.6\times 10^{-6}$ at the 90$\%$ confidence level. A CP asymmetry observable is constructed for the first two channels, which is measured to be $(-0.012\pm 0.054\pm 0.010)$ and $(0.062\pm 0.059\pm 0.006)$, respectively. No evidence for CP violation is observed in this process.

Comments: 9 pages, 1 figure