Observation and branching fraction measurement of the decay $J/\ddot{I}ˆ\to \bar{p}\hat{I}{\pounds }^{+}{K}_S^0+c.c.$

Abstract

The first observation of the decays $J/\ddot{I}ˆ\to \bar{p}\hat{I}{\pounds }^{+}{K}_S^0$ and $J/\ddot{I}ˆ\to p\bar{\hat{I}}{\pounds }^{-}{K}_S^0$ is reported using $(10087\pm 44)\times 10^6$ $J/\ddot{I}ˆ$ events recorded by the BESIII detector at the BEPCII storage ring. The branching fractions of each channel are determined to be $\mathcal{B}(J/\ddot{I}ˆ\to \bar{p}\hat{I}{\pounds }^{+}{K}_S^0)=(1.361\pm 0.006\pm 0.025)\times 10^{-4}$ and $\mathcal{B}(J/\ddot{I}ˆ\to p\bar{\hat{I}}{\pounds }^{-}{K}_S^0)=(1.352\pm 0.006\pm 0.025)\times 10^{-4}$. The combined result is $\mathcal{B}(J/\ddot{I}ˆ\to \bar{p}\hat{I}{\pounds }^{+}{K}_S^0+c.c.)=(2.725\pm 0.009\pm 0.050)\times 10^{-4}$, where the first uncertainty is statistical and the second systematic. The results presented are in good agreement with the branching fractions of the isospin partner decay $J/\ddot{I}ˆ\to p{K}^{-}\bar{\hat{I}}{\pounds }^0+c.c.$.