Observation of $\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\hat{I}\cdot$

Abstract

By analyzing $(27.12\pm 0.14)\times 10^8$ $\ddot{I}ˆ(3686)$ events accumulated with the BESIII detector, the decay $\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\hat{I}\cdot$ is observed for the first time with a significance of $6.2\ddot{I}ƒ$ after considering systematic uncertainties. The product of the branching fractions of $\ddot{I}ˆ(3686)\to {\hat{I}}^3\hat{I}{\cdot }_c(2S)$ and $\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\hat{I}\cdot$ is measured to be $\mathcal{B}(\ddot{I}ˆ(3686)\to {\hat{I}}^3\hat{I}{\cdot }_c(2S))\times \mathcal{B}(\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\hat{I}\cdot )=(2.39\pm 0.32\pm 0.34)\times 10^{-6}$, where the first uncertainty is statistical, and the second one is systematic. The branching fraction of $\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\hat{I}\cdot$ is determined to be $\mathcal{B}(\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\hat{I}\cdot )=(3.42\pm 0.46\pm 0.48\pm 2.44)\times 10^{-3}$, where the third uncertainty is due to the branching fraction of $\ddot{I}ˆ(3686)\to {\hat{I}}^3\hat{I}{\cdot }_c(2S)$. Using a recent BESIII measurement of $\mathcal{B}(\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\ddot{I}{€}^0)$, we also determine the ratio between the branching fractions of $\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\hat{I}\cdot$ and $\hat{I}{\cdot }_c(2S)\to K^{+}{K}^{-}\ddot{I}{€}^0$ to be $1.49\pm 0.22\pm 0.25$, which is consistent with the previous result of BaBar at a comparable precision level.