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| Charmonium states | |
|---|---|
| Name | Charmonium |
| Composition | charm–anticharm pair |
| Interaction | Strong interaction |
| Discovery | 1974 (November Revolution) |
| Notable | J/ψ, ψ(2S), η_c, χ_cJ |
Charmonium states Charmonium states are bound states of a charm quark and a anticharm antiquark produced and studied in high-energy experiments such as SLAC, CERN, and KEK. They provide precision tests of Quantum Chromodynamics and influenced discoveries like the J/ψ in the November Revolution that reshaped particle physics and affected programs at facilities including Brookhaven National Laboratory, Fermilab, and DESY. Measurements of charmonium connect to collaborations such as BaBar, Belle, LHCb, and theoretical groups at institutions like Institut des Hautes Études Scientifiques and Princeton University.
Charmonium arises from the binding of a charm and an anticharm via the Strong interaction in QCD. The spectrum includes well-known resonances such as the J/ψ, ψ(2S), η_c, and χ_cJ states, and is studied in experiments at CERN, SLAC, KEK, and BESIII. Historical milestones involve the simultaneous discoveries by teams at SLAC and BNL in 1974 during the November Revolution, earning Samuel C. C. Ting and Burton Richter the Nobel Prize in Physics.
Charmonium spectroscopy is organized by quantum numbers J^PC and radial excitation n, analogous to the hydrogen-like classification used in potential models developed at institutions like Cornell University and MIT. Prominent levels include the 1S states J/ψ and η_c, 2S state ψ(2S), and P-wave triplet χ_c0, χ_c1, χ_c2 measured by collaborations at CLEO, BaBar, and Belle. Spin-dependent splittings and hyperfine structure have been compared to predictions from models by theorists at SLAC, CERN, and Fermilab, while higher excitations like the 3S and D-wave states are explored by LHCb, BESIII, and Belle II.
Charmonium production occurs in processes at accelerators such as LHC experiments ATLAS, CMS, and LHCb, in e+e− annihilation at KEK and SLAC, and in photoproduction at HERA. Production mechanisms include prompt production in pp collisions studied by ALICE and quarkonium formation in heavy-ion collisions at RHIC examined by PHENIX and STAR. Decay channels involve electromagnetic transitions measured by BESIII and hadronic decays analyzed by CDF and D0, enabling determinations of branching fractions vital to programs at Jefferson Lab and TRIUMF.
Key discoveries include the simultaneous observation of the J/ψ by groups led by Samuel C. C. Ting at Brookhaven National Laboratory and Burton Richter at SLAC during the November Revolution. Precision spectroscopy has been advanced by detectors at CERN (including LHCb), KEK (including Belle and Belle II), SLAC (BaBar), and IHEP with BESIII. Masses and widths of states such as η_c, ψ(2S), and χ_cJ are tabulated by the Particle Data Group and refined by analyses from CLEO, BaBar, and Belle II. Measurements of production cross sections and polarization in experiments like CMS, ATLAS, and LHCb constrain theoretical descriptions developed at Princeton University and University of Chicago.
Potential models—Cornell, Godfrey–Isgur—developed at Cornell University and University of Cambridge describe the charmonium spectrum using a Coulomb-plus-linear confinement potential; comparisons are made with effective field theories such as Non-relativistic QCD (NRQCD) formulated by groups at MIT and Caltech. Lattice QCD calculations performed at collaborations involving Brookhaven National Laboratory, CERN, and Riken compute masses and transition rates ab initio, while perturbative QCD and techniques from Effective field theory groups at Stanford University and University of California, Berkeley address short-distance production and annihilation processes. Global fits and sum rules from theorists at Saclay and IHEP refine inputs such as quark masses and strong coupling constants.
Beyond conventional charmonium, the spectrum includes exotic candidates labeled XYZ discovered by experiments Belle, BaBar, BESIII, and LHCb. Examples include the X(3872), Y(4260), and charged Z_c states reported by teams at KEK and Cornell University. Interpretations involve tetraquark structures proposed by researchers at Ecole Polytechnique, hadronic molecules inspired by deuteron analogies, hybrid mesons with gluonic excitations studied at Jefferson Lab, and threshold effects analyzed by theorists at Perimeter Institute. Searches for pentaquark-like charm structures by LHCb connect to broader spectroscopy programs at CERN and J-PARC.
Charmonium studies impact determinations of parameters used across particle physics: the charm-quark mass, the α_s, and inputs to flavor experiments at KEK and CERN. Precision charmonium inputs constrain searches for new physics at LHC experiments ATLAS and CMS, inform heavy-ion programs at RHIC and LHC on deconfinement and quark–gluon plasma signatures measured by ALICE, and guide lattice collaborations at Brookhaven National Laboratory and Riken. The field fosters collaboration among institutions such as University of Oxford, Harvard University, Yale University, University of Tokyo, Max Planck Society, and promotes technological advances in detectors exemplified by upgrades at LHCb and Belle II.
Category:Mesons Category:Quarkonium