Charmonium and Charmoniumlike States at the BESIII Experiment

TL;DR

The BESIII experiment has made significant contributions to understanding charmonium and charmoniumlike states, including discovering new states, measuring transitions, and exploring their properties, advancing the field of heavy quarkonium spectroscopy.

Contribution

This review summarizes BESIII's recent experimental results on conventional and exotic charmonium states, highlighting new discoveries and insights into their structure and interactions.

Findings

First observation of $ ext{M1}$ transition $oldsymbol{\psi(3686) o \gamma \eta_c(2S)}$

Discovery of $oldsymbol{Z_c(3900)}$ and $oldsymbol{Z_c(4020)}$ tetraquark candidates

Evidence for commonality among $X(3872)$, $Y(4260)$, and $Z_c(3900)$ states

Abstract

Charmonium is a bound state of a charmed quark and a charmed antiquark, and a charmoniumlike state is a resonant structure that contains a charmed quark and antiquark pair but has properties that are incompatible with a conventional charmonium state. While operating at center-of-mass energies from 2 to 4.9 GeV, the BESIII experiment can access a wide mass range of charmonium and charmoniumlike states, and has contributed significantly in this field. We review BESIII results involving conventional charmonium states, including the first observation of M1 transition $\psi(3686) \to \gamma \eta_c(2S)$ and the discovery of the $\psi_2(3823)$; and report on studies of charmoniumlike states, including the discoveries of the $Z_c(3900)$ and $Z_c(4020)$ tetraquark candidates, the resolution of the fine structure of the $Y(4260)$, the discovery of the new production process $e^+e^-\to \gamma X(3872)$, and the uncovering of strong evidence for the commonality among the $X(3872)$, $Y(4260)$, and $Z_c(3900)$ states. The prospects for further research at BESIII and proposed future facilities are also presented.