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| Bottomonium states | |
|---|---|
| Name | Bottomonium states |
| Composition | Bottom quark–Antibottom quark |
| Family | Quarkonium |
| Quantum numbers | J^PC (varies) |
| Discovered | 1977 (ground state Upsilon (1S)) |
| Discovered by | E497 experiment; more generally E288 and Fermilab collaborations |
Bottomonium states Bottomonium states are bound states of a Bottom quark and an Antibottom quark, forming a heavy Quarkonium system analogous to Charmonium. They provide a testing ground for Quantum chromodynamics and Quantum Electrodynamics comparisons in the nonrelativistic regime, and they connect experimental programs at facilities such as CERN, Fermilab, KEK, DESY, and SLAC National Accelerator Laboratory.
Bottomonium states arise from the strong interaction between a Bottom quark and an Antibottom quark mediated by Gluon exchange within Quantum chromodynamics. The discovery of the ground state Upsilon (1S) by the E288 collaboration at Fermilab initiated detailed studies carried out at LHC experiments (including ATLAS, CMS, LHCb), at the SLAC National Accelerator Laboratory with PEP-II and BaBar, and at KEK with Belle and Belle II. Bottomonium spectroscopy complements results from Charmonium studies at BESIII and links to heavy-flavor physics programs at Brookhaven National Laboratory and IHEP.
Descriptions of bottomonium states employ nonrelativistic potential models, Lattice QCD, and Effective field theory approaches such as Nonrelativistic QCD (NRQCD) and Potential nonrelativistic QCD (pNRQCD). Calculations use inputs from the Strong interaction coupling constant α_s and incorporate Spin–orbit coupling, Hyperfine splitting, and Fine structure effects analogous to atomic physics but governed by Quantum chromodynamics. Perturbative expansions around heavy-quark mass scales invoke matching to full Quantum field theory calculations performed in collaborations like HPQCD and FNAL/MILC. Renormalization schemes developed by groups including MS-bar practitioners and phenomenologists from CERN Theory and INR inform predictions for masses, widths, and transition matrix elements.
Bottomonium spectroscopy is labeled with spectroscopic notation n^{2S+1}L_J producing states such as Upsilon (1S), Upsilon (2S), Upsilon (3S), and singlet counterparts like Eta_b (1S). Observed triplet and singlet states include P-wave Chi_b multiplets (e.g., Chi_b(1P), Chi_b(2P)) and D-wave candidates like Upsilon(1D). Excited states and radial excitations are cataloged by collaborations such as Particle Data Group and experiments at Belle II and LHCb. Fine and hyperfine splittings measured by CLEO, BaBar, and Belle test predictions from Lattice QCD teams like HPQCD and theoretical groups at Brookhaven National Laboratory and CERN Theory.
Production mechanisms include direct production in hadron colliders (LHC, Tevatron), as intermediate resonances in e^+e^- annihilation at KEK and SLAC National Accelerator Laboratory, and in heavy-ion collisions studied by ALICE. Prompt production, feed-down from higher states, and associated production with heavy-flavor jets are modeled using NRQCD and parton distribution functions from groups like CTEQ and MMHT. Decay modes encompass electromagnetic transitions (E1, M1) to lower bottomonia, hadronic annihilation into light hadrons via gluons, and radiative decays producing photons observed by BaBar and Belle. Weak decays are rare but connect to flavor physics programs at LHCb and Belle II, testing predictions of the Standard Model and constraining physics beyond the Standard Model explored by collaborations like ATLAS and CMS.
Measurements of masses, widths, branching fractions, and cross sections have been performed by E288, UA1, CDF, D0, CLEO, BaBar, Belle, Belle II, LHCb, ATLAS, CMS, and ALICE. Techniques include invariant-mass reconstruction of dilepton pairs (muon and electron channels), photon spectroscopy for radiative transitions, and inclusive analyses of hadronic final states. Detector technologies from Silicon Vertex Detector systems, Drift Chambers, Electromagnetic Calorimeters, and Muon Spectrometers developed at SLAC National Accelerator Laboratory and CERN enable precision that feeds into global fits by the Particle Data Group.
Bottomonium states serve as precision probes of Quantum chromodynamics in the nonperturbative regime, calibrants for heavy-flavor production models used by LHC experiments, and benchmarks for Lattice QCD methods validated by collaborations like HPQCD. They inform searches for exotic states (e.g., hybrids, tetraquarks) investigated by Belle and LHCb, and contribute to constraints on new physics scenarios explored at ATLAS and CMS, including studies related to Higgs boson couplings and Supersymmetry indirectly via precision fits performed by groups at CERN and national labs.
Outstanding issues include precise determination of higher radial and orbital excitations, nature of candidate exotic bottomonium-like states probed by Belle II and LHCb, and improved lattice determinations of matrix elements pursued by HPQCD and FNAL/MILC. Future upgrades at LHCb Upgrade, detector improvements at Belle II, and proposed facilities like the Electron–Ion Collider and future e^+e^- colliders hosted by institutions such as CERN and KEK aim to refine measurements of transition rates, production mechanisms, and search for novel dynamics beyond current Standard Model predictions investigated by collaborations including ATLAS, CMS, and theory groups across IFS and national laboratories.
Category:Quarkonium