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

Abstract

Using a data sample of $(1.0087\pm 0.0044)\times 10^{10}$ $J/\ddot{I}ˆ$ events collected with the BESIII detector, we study the rare double Dalitz decay of $\hat{I}\cdot \to e^{+}{e}^{-}{e}^{+}{e}^{-}$ through the processes $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}\cdot$ and $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{\cdot }^{\prime },\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}\cdot$. Clear $\hat{I}\cdot$ signals are observed in the $e^{+}{e}^{-}{e}^{+}{e}^{-}$ invariant mass spectrum, with statistical significances of 5.9$\ddot{I}ƒ$ and 7.8$\ddot{I}ƒ$ for the two channels, respectively. By combining both modes, we determine the branching fraction of $\hat{I}\cdot \to e^{+}{e}^{-}{e}^{+}{e}^{-}$ to be $(2.63\pm 0.34_{\mathrm{stat}}\pm 0.16_{\mathrm{syst}})\times 10^{-5}$. The result is consistent with the previous measurements within uncertainties and further constrains physics beyond the standard model.

11 pages, 5 figures, consistent with the Publication in PRD

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