Observation of $J/\ddot{I}ˆ$ decays to $e^{+}{e}^{-}{e}^{+}{e}^{-}$ and $e^{+}{e}^{-}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$

Abstract

Using a data sample of $4.481\times 10^8\ddot{I}{ˆ}^{\prime }$ events collected with the BESIII detector, we report the first observation of the four-lepton-decays $J/\ddot{I}ˆ\to e^{+}{e}^{-}{e}^{+}{e}^{-}$ and $J/\ddot{I}ˆ\to e^{+}{e}^{-}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ utilizing the process $\ddot{I}{ˆ}^{\prime }\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$. 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 $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$, 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.

9 pages, 1 figure