Observation of $\hat{I}{\cdot }_c\to \ddot{I}‰\ddot{I}‰$ in $J/\ddot{I}ˆ\to {\hat{I}}^3\ddot{I}‰\ddot{I}‰$

Abstract

Using a sample of $(1310.6\pm 7.0)\times 10^6$ $J/\ddot{I}ˆ$ events recorded with the BESIII detector at the symmetric electron positron collider BEPCII, we report the observation of the decay of the $(1^1{S}_0)$ charmonium state $\hat{I}{\cdot }_c$ into a pair of $\ddot{I}‰$ mesons in the process $J/\ddot{I}ˆ\to {\hat{I}}^3\ddot{I}‰\ddot{I}‰$. The branching fraction is measured for the first time to be $\mathcal{B}(\hat{I}{\cdot }_c\to \ddot{I}‰\ddot{I}‰)=(2.88\pm 0.10\pm 0.46\pm 0.68)\times 10^{-3}$, where the first uncertainty is statistical, the second systematic and the third is from the uncertainty of $\mathcal{B}(J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{\cdot }_c)$. The mass and width of the $\hat{I}{\cdot }_c$ are determined as $M=(2985.9\pm 0.7\pm 2.1)$MeV/$c^2$ and $\hat{I}“=(33.8\pm 1.6\pm 4.1)$MeV.

13 pages, 6 figures