Observation of $\hat{I}{\cdot }_c$ decay into $\hat{I}{\pounds }^{+}\bar{\hat{I}}{\pounds }^{-}$ and $\hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$ final states

Abstract

Using a data sample of $2.25\times 10^8$ $J/\ddot{I}ˆ$ events collected with the BESIII detector, we present the first observation of the decays of $\hat{I}{\cdot }_c$ mesons to $\hat{I}{\pounds }^{+}\bar{\hat{I}}{\pounds }^{-}$ and $\hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$. The branching fractions are measured to be $(2.11\pm 0.28_{stat.}\pm 0.18_{syst.}\pm 0.50_{\mathrm{PDG}})\times 10^{-3}$ and $(0.89\pm 0.16_{stat.}\pm 0.08_{syst.}\pm 0.21_{\mathrm{PDG}})\times 10^{-3}$ for $\hat{I}{\cdot }_c\to \hat{I}{\pounds }^{+}\bar{\hat{I}}{\pounds }^{-}$ and $\hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$, respectively. These branching fractions provide important information on the helicity selection rule in charmonium-decay processes.

17 pages, 8 figures