Zc(3900)

Zc(3900)
Name	Zc(3900)
Statistics	boson
Group	hadron
Status	observed
Mass	~3900 MeV/c^2
Width	~28–46 MeV
Charge	±1, 0
Spin	1?

Zc(3900) is an electrically charged hadronic resonance observed near 3.9 GeV/c^2 that has stimulated extensive study within Particle physics, Quark model, Large Hadron Collider-era experiments and B-factory facilities. First reported by collaborations working at the BESIII and Belle detectors, it challenges conventional Meson classification and has been interpreted as a candidate for an exotic tetraquark, hadronic molecule, or kinematic threshold effect. The state has been the subject of measurements by experiments such as BESIII, Belle, CLEO-c, LHCb, and theoretical analyses from groups associated with CERN, IHEP (Beijing), and various university groups.

Discovery and experimental observation

The initial signals were reported in processes studied at the BEPCII collider by the BESIII Collaboration and at the KEKB collider by the Belle Collaboration during analyses of e+e− annihilation into π+π−J/ψ and related channels, with corroborating studies by the CLEO-c Collaboration and followup searches at LHCb and CMS. These observations used detectors and facilities tied to institutions such as IHEP (Beijing), KEK, Cornell University, University of Oxford, and University of Rome La Sapienza. The resonance was extracted from invariant mass spectra employing analyses developed within collaborations including BESIII, Belle, BABAR, and theoretical input from groups at CERN and SLAC National Accelerator Laboratory.

Properties and quantum numbers

Measured properties include a mass near 3.9 GeV/c^2 and a relatively narrow width (tens of MeV) reported by BESIII and Belle, with charged states observed as ±1. Spin-parity assignments have been constrained by angular distributions studied by collaborations such as BESIII and LHCb, with J^P often favored as 1^+ in many analyses; determinations reference methods developed in Partial wave analysis and frameworks from Quantum chromodynamics phenomenology groups at institutions like IHEP (Beijing), CERN, and IHEP (Russia). Flavor content interpretations invoke charm and light quark degrees of freedom connected to the J/ψ and pion decay products measured in BESIII, Belle, and LHCb data sets.

Theoretical interpretations and models

Competing models discussed in literature from groups at CERN, IHEP (Beijing), University of Maryland, MIT, and Institute for Nuclear Theory include compact diquark–antidiquark tetraquark configurations, loosely bound D D* hadronic molecule scenarios, cusp or threshold effects related to S-matrix kinematics, and hybrid interpretations linked to exotic meson frameworks used in analyses by theorists at SLAC, DESY, University of Tokyo, and Princeton University. Lattice Quantum chromodynamics studies from collaborations tied to Fermilab and Brookhaven National Laboratory have attempted to probe multiquark correlations, while effective field theory approaches such as Heavy Quark Effective Theory and Chiral perturbation theory have been used by research groups at University of California, Berkeley, Yale University, and Columbia University.

Production and decay modes

Production has been observed in e+e− annihilation at center-of-mass energies near the Y(4260) region by BESIII and Belle, and in B meson decays studied by Belle and BABAR. Dominant decay channels include πJ/ψ and D D* final states analyzed by BESIII, Belle, LHCb, and CLEO-c using reconstruction techniques developed at KEK, SLAC National Accelerator Laboratory, and IHEP (Beijing). Searches for radiative and other hadronic transitions link the state to processes involving ψ(2S), η_c, and open-charm pairs, with branching-fraction constraints reported by collaborations associated with CERN, KEK, and IHEP (Beijing).

Experimental searches and confirmations

Independent confirmations of signals were pursued by BESIII, Belle, LHCb, CMS, and reanalyses by BABAR and CLEO-c groups; some datasets show clear peaks while others report tensions in significance or differing production rates. Global reviews and combined fits have been discussed at meetings hosted by ICHEP, Moriond Conference, Quark Matter Conference, and workshops at CERN and IHEP (Beijing), with input from analysis teams at Fermilab, Brookhaven National Laboratory, and university groups at University of Manchester, University of Bonn, and University of Padua.

Implications for exotic hadron spectroscopy

The resonance has driven renewed interest in exotic spectroscopy alongside states like X(3872), Y(4260), and charged Z states reported by Belle and BABAR, motivating theoretical and experimental programs at LHCb, BESIII, Belle II, and PANDA. Its properties inform models of multiquark dynamics explored at CERN, SLAC National Accelerator Laboratory, DESY, and university theory centers such as Institute for Advanced Study and Perimeter Institute, influencing searches for analogous states in bottomonium studied by Belle II and charmoniumlike searches at LHCb.

Open questions and future directions

Key open questions remain: precise quantum numbers, internal structure (compact tetraquark versus molecule versus cusp), production mechanisms in B decays versus e+e− annihilation, and relations to other XYZ states; these are being targeted by upcoming data from Belle II, extended runs at BEPCII with BESIII, analyses at LHCb and CMS, and planned studies at PANDA and future Electron–Ion Collider. Continued input from lattice Quantum chromodynamics groups at CERN and Fermilab, effective-field-theory practitioners at MIT and University of California, Berkeley, and global experimental collaborations will be required to resolve the nature of this resonance.

Category:Exotic hadrons