First observation of the $\hat{I}{\cdot }_c\to \hat{I}{ž}^0\bar{\hat{I}}{ž}^0$ decay

Abstract

Using $(10087\pm 44)\times 10^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the decay $\hat{I}{\cdot }_c\to \hat{I}{ž}^0\bar{\hat{I}}{ž}^0$. The interference between $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{\cdot }_c\to {\hat{I}}^3\hat{I}{ž}^0\bar{\hat{I}}{ž}^0$ and $J/\ddot{I}ˆ\to {\hat{I}}^3\hat{I}{ž}^0\bar{\hat{I}}{ž}^0{|}_{\mathrm{non}-\mathrm{resonance}}$ is considered in the $\hat{I}{ž}^0\bar{\hat{I}}{ž}^0$ mass spectrum fits. The branching fractions are measured to be $B(\hat{I}{\cdot }_c\to \hat{I}{ž}^0\bar{\hat{I}}{ž}^0)=(1.33\pm 0.03\pm 0.18)\times 10^{-3}$ for the constructive interference and $B(\hat{I}{\cdot }_c\to \hat{I}{ž}^0\bar{\hat{I}}{ž}^0)=(1.63\pm 0.04\pm 0.21)\times 10^{-3}$ for the destructive interference, where the first uncertainties are statistical and the second are systematic.