Measurement of the branching fraction of $\hat{I}\cdot \to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ and search for $\hat{I}\cdot \to e^{+}{e}^{-}$

Abstract

We analyze the decay of $\hat{I}\cdot \to {\ell }^{+}{\ell }^{-}(\ell =e,\hat{I}¼)$ via $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{\cdot }^{\prime }$ and $\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\hat{I}\cdot$, based on (10087 $\pm$ 44) $\times$ 10${}^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector at the BEPCII storage rings. The branching fraction of $\hat{I}\cdot \to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ is measured to be $(5.8\pm 1.0_{\mathrm{stat}}\pm 0.2_{\mathrm{syst}})\times 10^{-6}$, which is consistent with the previous measurements and theoretical expectations. In addition, no significant $\hat{I}\cdot \to e^{+}{e}^{-}$ signal is observed in the $e^{+}{e}^{-}$ invariant mass spectrum, and an improved upper limit of $\mathcal{B}(\hat{I}\cdot \to e^{+}{e}^{-})<2.2\times 10^{-7}$ is set at 90\% confidence level.

10 pages, 6 figures