Charmonium in China: BEPCII/BESIII

TL;DR

This paper reports extensive charmonium measurements from BESIII at BEPCII, confirming previous findings and providing new insights into decay processes, branching ratios, and meson mixing with large data samples.

Contribution

It presents the first measurements of certain branching ratios and observations of new processes in charmonium physics using large BESIII datasets.

Findings

Confirmation of p̄p threshold enhancement in J/ψ decays

First measurements of ψ' → π^0 h_c and h_c → γ η_c branching ratios

Observation of the two-photon process ψ' → γγ J/ψ

Abstract

Results based on 106 M $\psi'$ events and about 226 M $J/\psi$ events acquired with the BESIII detector at BEPCII are reported, including a confirmation of the BESII $p\bar{p}$ threshold enhancement in $J/\psi \to \gamma p\bar{p}$, branching ratios for $\chi_{cJ} \to \pi^0 \pi^0$ and $\eta \eta$, and first measurements of the branching ratios for $\psi' \to \pi^0 h_c$ and $h_c \to \gamma \eta_c$, as well as measurements of the mass and width of the $h_c$. Also reported are first observations of the two photon process $\psi' \to \gamma \gamma J/\psi$ and $f_0(980) - a_0(980)$ mixing.