Observation of the double Dalitz decay $\hat{I}{\cdot }^{\prime }\to e^{+}{e}^{-}{e}^{+}{e}^{-}$

Abstract

Based on $(10087\pm 44)\times 10^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector at BEPCII, the double Dalitz decay $\hat{I}{\cdot }^{\prime }\to e^{+}{e}^{-}{e}^{+}{e}^{-}$ is observed for the first time via the $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{\cdot }^{\prime }$ decay process. The significance is found to be 5.7$\ddot{I}ƒ$ with systematic uncertainties taken into consideration. Its branching fraction is determined to be $\mathcal{B}(\hat{I}{\cdot }^{\prime }\to e^{+}{e}^{-}{e}^{+}{e}^{-})=(4.5\pm 1.0(stat.)\pm 0.5(sys.))\times 10^{-6}$.