Zc(3900)

Zc(3900) refers to a charged charmonium-like resonance observed in the invariant mass spectrum of the π±J/ψ final state in the decay of Y(4260) by the BESIII experiment in 2013. It is considered an exotic hadron candidate because its minimal quark content is ccud, indicating it is not a conventional meson or baryon. The "Zc" notation signifies a charged (c) charmonium-like (Z) state. The number (3900) indicates its approximate mass in MeV.

The discovery of Zc(3900) sparked considerable interest in the high-energy physics community, as it suggested the existence of tetraquarks or other more complex hadronic structures beyond the standard quark-antiquark meson or three-quark baryon configurations. Several other experiments, including Belle, have subsequently confirmed the existence of this resonance.

The properties of Zc(3900), such as its mass, width, spin, and parity, are still under investigation. Various theoretical models have been proposed to explain its nature, including tetraquark, molecular meson, and hadroquarkonium scenarios. However, a definitive understanding of its internal structure remains elusive. The experimental and theoretical study of Zc(3900) and similar exotic hadrons continues to be an active area of research in particle physics.