Observation and branching fraction measurement of the decay $J/\psi \to \overline{p}{\Sigma }^{+}{K}_S^0+c.c.$

The first observation of the decays $J/\psi \to \overline{p}{\Sigma }^{+}{K}_S^0$ and $J/\psi \to p{\overline{\Sigma }}^{-}{K}_S^0$ is reported using $(10087\pm 44)\times {10}^{6}J/\psi$ events recorded by the BESIII detector at the BEPCII storage ring. The branching fractions of each channel are determined to be $B\left(J/\psi \to \overline{p}{\Sigma }^{+}{K}_S^0\right)=(1.361\pm 0.006\pm 0.025)\times {10}^{-4}$, and $B\left(J/\psi \to p{\overline{\Sigma }}^{-}{K}_S^0\right)=(1.352\pm 0.006\pm 0.025)\times {10}^{-4}$. The combined result is $B(J/\psi \to \overline{p}{\Sigma }^{+}{K}_S^0+c.c.)=(2.725\pm 0.009\pm 0.050)\times {10}^{-4}$, 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 $J/\psi \to p{K}^{-}{\overline{\Sigma }}^0+c.c.$