Discovery of XYZ particles at the BESIII Experiment

Abstract

Charmonium is a bound state of a charmed quark and a charmed antiquark, and a charmoniumlike state is a resonant structure that contains at least a charmed quark-antiquark pair but has properties that are incompatible with a conventional charmonium state. The charmoniumlike states are also called XYZ particles to indicate their underlying nature is still unclear. The BESIII experiment has contributed significantly in the study of the XYZ particles, and here we review the discoveries of the Zc(3900), Zc(4020), and Zcs(3985) tetraquark states and the observations of several new vector charmoniumlike states at the BESIII experiment.