charmonium

charmonium
Dirk Hünniger, Joel Holdsworth · CC BY-SA 3.0 · source
Name	Charmonium
Composition	charm quark–anticharm quark pair
Type	Meson
Discovered	1974
Discovered by	SLAC National Accelerator Laboratory, Brookhaven National Laboratory
Mass	variable (state-dependent)
Spin	0 or 1 (state-dependent)

charmonium is a family of mesons composed of a charm quark and a charm antiquark bound by the strong interaction. These states played a central role in the November Revolution of 1974 and remain a key testing ground for Quantum Chromodynamics and models of quark confinement. Experimental programs at major facilities and theoretical work across institutions have mapped many levels of the spectrum and provided precision tests of perturbative and nonperturbative techniques.

Overview

Charmonium states include low-lying and excited resonances observed in various reactions at facilities such as SLAC National Accelerator Laboratory, Brookhaven National Laboratory, CERN, Fermilab, and KEK. Observed signals like the J/ψ and ψ' were crucial for collaborations including groups at Stanford Linear Accelerator Center, Columbia University, Harvard University, University of California, Berkeley, Massachusetts Institute of Technology, and Princeton University. Measurements by detectors such as MARK I, CLEO, BaBar, Belle, BESIII, LHCb, ATLAS, and CMS provided branching fractions, cross sections, and lineshapes used by theorists at institutions like Institute for Advanced Study, CERN Theory Division, SLAC Theory Group, and Perimeter Institute.

History of Discovery and Experiments

The simultaneous observations of the J/ψ resonance by teams at SLAC National Accelerator Laboratory (the MARK I collaboration) and Brookhaven National Laboratory (led by Samuel Ting) marked a watershed recognized by the Nobel Prize in Physics awarded to Burton Richter and Samuel C. C. Ting. Follow-up experiments at DESY, CERN, Fermilab, KEK, and Novosibirsk extended spectroscopy via e+e− annihilation and hadroproduction; important experiments include work by MARK II, ARGUS, CLEO-c, Belle II, and BESIII. Accelerator projects and collaborations such as SLAC, Brookhaven National Laboratory, Fermilab, CERN, KEK, and DESY pushed precision measurements, while theorists from Stanford University, Cornell University, MIT, Caltech, University of Chicago, and Columbia University interpreted results.

Spectroscopy and States

The spectrum contains vector states like J/ψ and ψ(2S), spin-singlet states such as η_c, and higher orbital and radial excitations including χ_cJ triplets and ψ(3770). Experiments at CLEO, BaBar, Belle, BESIII, LHCb, and CDF mapped resonances, uncovered thresholds near D meson pairs studied at BABAR and Belle II, and identified exotic candidates investigated by groups at LHCb, CMS, and ATLAS. Spectroscopic classification uses notations from Particle Data Group listings and comparisons to heavy quarkonia systems like bottomonium measured at Belle and BaBar. States interact with open-charm channels such as D, D*, D_s observed by collaborations including CLEO-c and BESIII.

Theoretical Models and Calculations

Potential models inspired by early work at institutions like Cornell University and Argonne National Laboratory used phenomenological potentials to reproduce level spacings. Effective field theories developed at CERN Theory Division, SLAC Theory Group, Perimeter Institute, and Institute for Advanced Study—including Nonrelativistic QCD and potential NRQCD—connect short-distance coefficients computed by groups at Massachusetts Institute of Technology, Stanford University, Harvard University, and University of Oxford with long-distance matrix elements. Sum rule approaches from researchers associated with Budker Institute of Nuclear Physics and Institute for Nuclear Theory complement lattice studies by collaborations at Fermilab Lattice, RBC/UKQCD, and HPQCD. Perturbative calculations of annihilation rates and radiative transitions were pursued by theorists at IPN Orsay, CEA Saclay, and KEK.

Production and Decay Mechanisms

Production mechanisms in e+e− annihilation at SLAC National Accelerator Laboratory and KEK contrast with hadroproduction at Fermilab and CERN Large Hadron Collider, where experiments such as CDF, D0, LHCb, ATLAS, and CMS measured prompt and nonprompt yields. Baryon and meson decays studied at Belle, BaBar, LHCb, and BESIII reveal feed-down patterns from higher charmonia to J/ψ and η_c. Radiative transitions, hadronic transitions, and annihilation processes were modeled by theorists at University of Cambridge, Imperial College London, University of Glasgow, and Trinity College Dublin. Studies of polarization and spin alignment involved collaborations at RHIC and LHC experiments, with input from groups at Brookhaven National Laboratory and Jefferson Lab.

Lattice QCD and Computational Studies

Lattice QCD computations by collaborations such as Fermilab Lattice (FNAL/MILC), RBC/UKQCD, HPQCD, and groups at Institute for Theoretical Physics, Utrecht used gauge configurations from supercomputing centers including Oak Ridge National Laboratory, Lawrence Livermore National Laboratory, Argonne National Laboratory, and CERN IT Department. These studies compute masses, hyperfine splittings, and matrix elements relevant for decays; comparisons are made to experimental numbers from Particle Data Group compilations and analyses by PDG Working Group convened with researchers at CERN and Brookhaven National Laboratory. Numerical techniques developed at Los Alamos National Laboratory and NERSC underpin high-precision calculations.

Applications and Implications in Particle Physics

Charmonium provides a precision laboratory for testing Quantum Chromodynamics in both perturbative regimes studied at CERN Theory Division and nonperturbative regimes addressed by Rutherford Appleton Laboratory and DESY. Measurements constrain parton distribution functions used by ATLAS and CMS and inform heavy-flavor tagging at LHCb and Tevatron experiments. Searches for exotic hadrons—including tetraquark and hybrid candidates—were led by teams at Belle, BaBar, LHCb, BESIII, and CMS and have implications for models developed at Perimeter Institute and Institute for Advanced Study. Precision charmonium studies intersect with electroweak probes at Jefferson Lab and contribute to determinations of fundamental parameters pursued by researchers at Stanford Linear Accelerator Center and European Organization for Nuclear Research.

Category:Mesons Category:Heavy quarkonia