Observation of the decay $\psi (3686)\to {\mathrm{\Sigma }}^{-}{\bar{\mathrm{\Sigma }}}^{+}$ and measurement of its angular distribution

Using $(448.1\pm 2.9)\times {10}^6$ $\psi (3686)$ events collected with the BESIII detector at the BEPCII collider, the decay $\psi (3686)\to {\mathrm{\Sigma }}^{-}{\bar{\mathrm{\Sigma }}}^{+}$ is observed for the first time with a branching fraction of $(2.82\pm {0.04}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {0.08}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\times {10}^{-4}$, and the angular parameter ${\alpha }_{{\mathrm{\Sigma }}^{-}}$ is measured to be $0.96\pm {0.09}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {0.03}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}}$.