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| χ_cJ | |
|---|---|
| Name | χ_cJ |
| Other names | chi_cJ |
| Composition | charm quark–anticharm quark |
| Spin | 0, 1, 2 |
χ_cJ
χ_cJ are a family of charmonium states observed in experiments at facilities such as CERN, Fermilab, SLAC, KEK, and DESY. These mesons, composed of a charm quark and a charm antiquark, appear alongside other states like J/ψ, ψ(2S), and η_c in the spectroscopy of heavy quarkonia studied by collaborations including LHCb, ATLAS, CMS, Belle, and BaBar. Measurements at machines such as the Large Hadron Collider, Tevatron, and BEPCII have characterized their masses and widths, connecting χ_cJ to theoretical frameworks developed by groups at CERN Theory Division, Brookhaven National Laboratory, and IHEP.
The χ_cJ notation denotes triplet P-wave charmonium states with total angular momentum J = 0, 1, 2, related to spectroscopic labels from potential models and the spectroscopic notation used in texts from authors at Cornell University, MIT, and Caltech. Quantum numbers associated with χ_c0, χ_c1, and χ_c2 include spin-parity-charge conjugation assignments J^{PC} = 0^{++}, 1^{++}, 2^{++}, consistent with classification schemes discussed by theorists at CERN, University of Chicago, and Princeton University. The χ_cJ resonances are partners to states like h_c and fit into multiplets predicted by Quantum Chromodynamics calculations from groups at Stanford University, University of Oxford, and University of Tokyo.
Production mechanisms for χ_cJ include radiative transitions from higher charmonium such as ψ(2S), hadroproduction in collisions at LHC, and two-photon fusion explored at KEK and SLAC. Decay channels involve radiative decays to J/ψ, hadronic transitions to light mesons measured by Belle II and BESIII, and annihilation into gluons studied in analyses by teams at CERN and Fermilab. Prominent decay modes observed by collaborations like CLEO include χ_cJ → γ J/ψ and χ_cJ → ππ, K K̄, with branching fractions compared across results from LHCb, BaBar, and Belle.
Experimental determinations of χ_cJ masses and widths have relied on datasets from detectors such as CMS, ATLAS, LHCb, BaBar, Belle, and BESIII. Early signals were reported in experiments at SLAC and CERN and refined by analyses at Fermilab and KEK. Precision spectroscopy exploiting techniques developed at Brookhaven National Laboratory and instrumentation from DESY provided mass splittings between χ_cJ states and other charmonia like ψ(3770), informing global fits maintained by collaborations at Particle Data Group and groups at Imperial College London.
Models interpreting χ_cJ employ nonrelativistic potential models originating from researchers at Cornell University and University of Oxford, effective field theories such as Nonrelativistic QCD developed by theorists at MIT and Harvard University, and lattice QCD computations from groups at RIKEN, Fermilab, and CERN. Calculations of hyperfine and fine structure splittings reference works by authors at Caltech, University of Illinois Urbana–Champaign, and University of Cambridge. Phenomenological descriptions incorporate spin-orbit and tensor interactions whose parameters are constrained by fits carried out by collaborations at SLAC and LHCb.
Measurements of χ_cJ exploit electromagnetic calorimetry and tracking systems in detectors such as CMS, ATLAS, LHCb, Belle II, and BESIII, with photon reconstruction performed using technologies developed at KEK and DESY. Trigger strategies and vertexing algorithms from teams at CERN and SLAC enable selection of radiative transitions like ψ(2S) → γ χ_cJ. Analyses use partial wave analysis techniques and maximum-likelihood fits common to groups at Fermilab, Brookhaven National Laboratory, and Cornell University to disentangle overlapping resonances and to measure angular distributions tied to spin assignments.
χ_cJ states provide crucial tests of Quantum Chromodynamics in the nonperturbative regime, complementary to studies of bottomonium at facilities like KEK and SLAC. They serve as benchmarks for lattice QCD computations from collaborations at CERN and RIKEN and as inputs for understanding quarkonium production mechanisms in heavy-ion collisions investigated by ALICE and STAR. Precision knowledge of χ_cJ spectroscopy informs searches for exotic states such as tetraquarks and hybrids pursued by LHCb, Belle II, and BESIII, and impacts determinations of fundamental parameters discussed at workshops held by ICHEP and EPS-HEP.