Precision Studies of the $\eta_c$ decay at BESIII

The lowest lying charmonium system $\eta_c$ has been observed for more than four decades. Studies of its production and decay properties provide an unique platform to investigate the inner structure of charmonium systems, hence improve our understanding of strong interaction in the charm sector. BESIII detector at the $e^+e^-$ BEPCII collider has already collected the world largest $J/\psi$ and $\psi(3686)$ data sets, based on which massive $\eta_c$ samples are produced via radiative transitions. This paper reviews recent precision studies of the $\eta_c$ decays at BESIII, including $J/\psi\to\gamma\eta_c$, $\eta_c\to\gamma\gamma$, and several $\eta_c$ hadronic decays.