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| Υ(6S) | |
|---|---|
| Name | Υ(6S) |
| Type | Meson |
| Family | Bottomonium |
| Composition | b b̄ |
| Mass | ≈10.99 GeV/c^2 |
| Width | O(10–100) MeV |
Υ(6S).
The Υ(6S) is an excited state of bottomonium, a bound state of a bottom quark and anti-bottom quark associated with the Quark model, heavy-quark spectroscopy and the study of Quantum Chromodynamics. As a vector resonance it participates in electromagnetic production in e+e− annihilation and couples to hidden-bottom final states studied at colliders and detectors such as Belle II, Belle, BaBar, CLEO and LHCb. Investigations of the Υ(6S) impact understanding of potential models, lattice Quantum chromodynamics, and effective field theories like Non-relativistic QCD.
Evidence for the Υ(6S) emerged from energy scans and resonance studies in e+e− collisions carried out at KEKB, PEP-II, CESR, and later at SuperKEKB. Early spectroscopy of bottomonium was driven by experiments including ARGUS and Crystal Ball; later clearer signals and cross-section measurements came from Belle and BaBar. Observations were made through inclusive hadronic cross sections, radiative transitions, and exclusive channels involving bottomonia such as Υ(nS) transitions and open-bottom pairs, with corroborating analyses from Fermilab-based research programs and international collaborations like IHEP groups.
The Υ(6S) is conventionally assigned quantum numbers J^PC = 1^−− consistent with a vector bottomonium state in the spectroscopic notation n^3S_1. Its approximate mass near 10.99 GeV/c^2 and total width reflect thresholds for open-bottom production including B^(*)B^(*) channels and interactions with light-quark pairs from vacuum polarization. The state is described within potential models such as the Cornell potential and relativized quark models by groups like Godfrey and Isgur, while lattice calculations from collaborations including HPQCD and FNAL/MILC provide complementary determinations of masses and splittings.
The Υ(6S) decays predominantly to open-bottom final states, including B\bar{B}, B\bar{B}^*, B^*\bar{B}^*, and B_s^{(*)}\bar{B}_s^{(*)}, with branching fractions sensitive to phase space and coupled-channel effects. Radiative transitions to lower bottomonia such as χ_bJ and Υ(nS) lead to photons and subsequent cascade decays observed in detectors like CLEO-c and Belle II. Hadronic transitions involving light mesons (ππ, η) connect Υ(6S) to Υ(1S), Υ(2S), and Υ(3S) with branching patterns studied by collaborations including BESIII and CMS. Leptonic partial widths to e+e−, μ+μ− and τ+τ− are small but measurable and benchmark comparisons are made with theoretical predictions from NRQCD and potential-model leptonic width formulas.
Υ(6S) production occurs in e+e− annihilation at center-of-mass energies tuned to the resonance at machines such as KEKB and SuperKEKB; initial-state radiation at experiments like BaBar and Belle also produces Υ(6S) events. In hadronic environments, production can occur via fragmentation and feed-down from higher-mass states at LHC experiments including ATLAS, CMS, and LHCb where heavy-flavor triggers and vertexing isolate bottomonium decays. Photoproduction studies at facilities inspired by HERA concepts and proposed electron-ion colliders explore alternative production mechanisms, while fixed-target experiments at J-PARC and CERN SPS offer complementary probes.
The Υ(6S) is interpreted in quarkonium phenomenology as a high radial excitation of the b b̄ system, but its properties raise questions about coupled-channel dynamics, threshold effects, and mixing with hybrid or molecular configurations proposed in models by groups such as Eichten-Quigg analyses and studies by Brambilla et al.. Coupled-channel and unitarized approaches incorporate interactions with open-bottom channels and light-quark pair creation modeled by the ^3P_0 model and other hadronization schemes. Effective-field-theory descriptions use pNRQCD and lattice input from RBC and UKQCD to address spin-dependent splittings and nonperturbative contributions.
Measurements of Υ(6S) mass, width, and cross sections have been reported by Belle, BaBar, CLEO, and corroborated by global analyses at the Particle Data Group; upcoming high-luminosity runs at SuperKEKB and analyses at Belle II aim to refine branching fractions and rare transition rates. Complementary studies at LHCb and ATLAS expand reach into production in hadronic collisions, while planned theoretical-experimental collaborations involving CERN groups and national laboratories such as KEK, SLAC, and Brookhaven National Laboratory coordinate future efforts. Continued interplay with lattice collaborations like HPQCD and MILC will tighten comparisons between measured spectra and first-principles QCD computations.
Category:Bottomonium Category:Mesons Category:Quarkonia