Observation of $\psi (3686)\to {\Xi }^{-}{K}_S^0{\bar{\Omega }}^{+}$+c.c

Abstract

Using a sample of $(2.712\pm 0.014)\times 10^9$ $\psi (3686)$ events collected with the BESIII detector at the electron positron collider BEPCII, the decay $\psi (3686)\to {\Xi }^{-}{K}_S^0{\bar{\Omega }}^{+}+c.c.$ is observed for the first time, which has a significance of 5.9 standard deviations. The branching fraction of this decay is measured to be $(2.91\pm 0.47\pm 0.33)\times 10^{-6}$, where the first and second uncertainties are statistical and systematic, respectively. The ratio between ${\mathcal{B}}_{\psi (3686)\to {\Xi }^{-}{K}_S^0{\bar{\Omega }}^{+}+c.c.}$ and ${\mathcal{B}}_{\psi (3686)\to {\Omega }^{-}{K}^{+}{\bar{\Xi }}^0+c.c.}$ is determined to be $1.05\pm 0.23\pm 0.14$, which deviates with the isospin symmetry conservation predicted value of 0.5 by $2.1\sigma$.