Measurements of charmonia decays from BESIII

TL;DR

This paper reports precise measurements of various charmonium decay processes using BESIII data, including branching fractions, polarization parameters, and first evidence of certain decay modes, advancing understanding of charmonium physics.

Contribution

The study provides the most precise measurements of $ ext{chi}_{cJ} o ext{phi} ext{phi}$ branching fractions and polarization, first evidence of $ ext{eta}_c(2S) o ext{pi}^+ ext{pi}^- ext{eta}$, and observes $ ext{chi}_{cJ} o ext{Omega}^- ar{ extOmega}^+$ decays for the first time.

Findings

Measured $ ext{chi}_{cJ} o ext{phi} ext{phi}$ branching fractions precisely.

First evidence of $ ext{eta}_c(2S) o ext{pi}^+ ext{pi}^- ext{eta}$ decay.

Observed $ ext{chi}_{cJ} o ext{Omega}^- ar{ extOmega}^+$ decays for the first time.

Abstract

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 $e^+ e^- \to \eta J/\psi$ 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 $\psi(3770) \to \eta J/\psi$ 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 $\chi_{cJ} \to \Omega^- \bar{\Omega}^+(J=0,1,2)$ 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.