Measurements of charmonia decays from BESIII

Abstract

In this talk, recent measurements of charmonium decays of BESIII are presented. Using 448 million $ψ(3686)$ events collected with the BESIII detector, the branching fractions of the decays $χ_{cJ} \to ϕϕ(J=0,1,2)$ have been measured most precisely, and the polarization parameters of $χ_{cJ} \to ϕϕ$ 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 $η_c(2S) \to π^+ π^- η$ has been found in the decay sequence $ψ(3686) \to γη_c(2S)(\to π^+ π^- η)$. The product of the branching fractions of $ψ(3686) \to γη_c(2S)$ and $η_c(2S) \to π^+ π^- η$ is reported as well as the individual branching fraction of $η_c(2S) \to π^+ π^- η$. The process $e^+ e^- \to ηJ/ψ$ at a center-of-mass energy $3.773~{\rm GeV}$ is observed for the first time. Its Born cross-section is measured, and the branching fraction of $ψ(3770) \to ηJ/ψ$ 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 $ψ(3686)$ events collected by the BESIII detector, the decays $χ_{cJ} \to Ω^- \barΩ^+(J=0,1,2)$ have been observed for the first time with high significance via the radiative decays of $ψ(3686) \to γχ_{cJ}$. The relevant branching fractions have been provided.