Observation of ${\eta }_c$ decay into ${\mathrm{\Sigma }}^{+}{\bar{\mathrm{\Sigma }}}^{-}$ and ${\mathrm{\Xi }}^{-}{\bar{\mathrm{\Xi }}}^{+}$ final states

Using a data sample of $2.25\times {10}^8$ $J\mathrm{/}\psi$ events collected with the BESIII detector, we present the first observation of the decays of ${\eta }_c$ mesons to ${\mathrm{\Sigma }}^{+}{\bar{\mathrm{\Sigma }}}^{-}$ and ${\mathrm{\Xi }}^{-}{\bar{\mathrm{\Xi }}}^{+}$. The branching fractions are measured to be $(2.11\pm0.28_{\rm stat.}\pm0.18_{\rm syst.}\pm0.50_{\rm PDG})\times10^{-3}$and$(0.89\pm0.16_{\rm stat.}\pm0.08_{\rm syst.}\pm0.21_{\rm PDG})\times10^{-3}$for$\eta_{c} \to \Sigma^{+}\bar{\Sigma}^{-}$and$\Xi^{-}\bar{\Xi}^{+}$, respectively. These branching fractions provide important information on the helicity selection rule in charmonium-decay processes.