Zc3900

Zc(3900) is a charged charmonium-like hadron that was discovered in 2013 by the BESIII collaboration and subsequently confirmed by the Belle experiment. It appeared in e+ e- collisions producing a π± J/ψ final state near a center-of-mass energy of 4.26 GeV, manifested as a peak in the J/ψ π± invariant mass around 3.9 GeV. Early measurements place its mass near 3899 MeV with a width of tens of MeV, typically in the range of 40–60 MeV depending on the analysis. The charged nature of Zc(3900) rules out a conventional quark-antiquark meson, implying a minimal quark content of at least four quarks, such as c c̄ u d̄, marking it as an exotic hadron candidate.

The quantum numbers of Zc(3900) have not been definitively established; analyses generally allow J^P = 1^+ as a plausible assignment, consistent with its decay to J/ψ π. The nature of the state remains the subject of interpretation and debate. Competing explanations include a compact tetraquark configuration (a tightly bound diquark–antidiquark state), a hadronic molecule formed from D D̄* (or D* D̄) pairs, or a kinematic threshold effect that mimics a resonance rather than a true bound state.

Zc(3900) is part of a broader family of charged charmonium-like states observed in the charm sector, such as Zc(3885), Zc(4020), and Zc(4025). These states have motivated extensive theoretical and experimental investigation into multiquark dynamics and the spectrum of exotic hadrons. Ongoing measurements aim to clarify its internal structure, production mechanisms, and its relationship to other Zc states.