Measurements of charmonia decays from BESIII

In this talk, recent measurements of charmonium decays of BESIII are presented. Using 448 million $\psi (3686)$ events collected with the BESIII detector, the branching fractions of the decays ${\chi }_{cJ}\to \phi \phi (J=0,1,2)$ have been measured most precisely, and the polarization parameters of ${\chi }_{cJ}\to \phi \phi$ have been determined for the first time via a helicity amplitude analysis. Using the same data sample as in the previous study, first evidence of ${\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta$ has been found in the decay sequence $\psi (3686)\to \gamma {\eta }_c(2S)(\to {\pi }^{+}{\pi }^{-}\eta )$. The product of the branching fractions of $\psi (3686)\to \gamma {\eta }_c(2S)$ and ${\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta$ is reported as well as the individual branching fraction of ${\eta }_c(2S)\to {\pi }^{+}{\pi }^{-}\eta$. The process $e^{+}{e}^{-}\to \eta J\mathrm{/}\psi$ at a center-of-mass energy $3.773\mathrm{G}\mathrm{e}\mathrm{V}$ is observed for the first time. Its Born cross-section is measured, and the branching fraction of $\psi (3770)\to \eta J\mathrm{/}\psi$ is determined by a combined fit with the cross sections at other energy points, after considering the interference effect for the first time. Utilizing 2708 million $\psi (3686)$ events collected by the BESIII detector, the decays ${\chi }_{cJ}\to {\mathrm{\Omega }}^{-}{\bar{\mathrm{\Omega }}}^{+}(J=0,1,2)$ have been observed for the first time with high significance via the radiative decays of $\psi (3686)\to \gamma {\chi }_{cJ}$. The relevant branching fractions have been provided.