Observation and branching fraction measurement of the decay $J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi \to \bar{p}{\mathrm{\Sigma }}^{+}{K}_S^0+c\mathrm{.}c\mathrm{.}$

The first observation of the decays $J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi \to \bar{p}{\mathrm{\Sigma }}^{+}{K}_S^0$ and $J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi \to p{\bar{\mathrm{\Sigma }}}^{-}{K}_S^0$ is reported using $(10087\pm 44)\times {10}^6$ $J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi$ events recorded by the BESIII detector at the BEPCII storage ring. The branching fractions of each channel are determined to be $\mathcal{B}(J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi \to \bar{p}{\mathrm{\Sigma }}^{+}{K}_S^0)=(1.361\pm 0.006\pm 0.025)\times {10}^{-4}$ and $\mathcal{B}(J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi \to p{\bar{\mathrm{\Sigma }}}^{-}{K}_S^0)=(1.352\pm 0.006\pm 0.025)\times {10}^{-4}$. The combined result is $\mathcal{B}(J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi \to \bar{p}{\mathrm{\Sigma }}^{+}{K}_S^0+c\mathrm{.}c\mathrm{.})=(2.725\pm 0.009\pm 0.050)\times {10}^{-4}$, 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 $J\text{\hspace{0.17em}⁣}\mathrm{/}\text{\hspace{0.17em}⁣}\psi \to p{K}^{-}{\bar{\mathrm{\Sigma }}}^0+c\mathrm{.}c\mathrm{.}$.