Guy Wilkinson

Abstract:

© 2020, CERN for the benefit of the LHCb collaboration. Using a data sample corresponding to an integrated luminosity of 2.0 fb-1, collected by the LHCb experiment, the production of the ηc(1 S) state in proton–proton collisions at a centre-of-mass energy of s=13TeV is studied in the rapidity range 2.0 < y< 4.5 and in the transverse momentum range 6.5<pT<14.0GeV. The cross-section for prompt production of ηc(1 S) mesons relative to that of the J/ ψ meson is measured using the pp¯ decay mode and is found to be σηc(1S)/σJ/ψ=1.69±0.15±0.10±0.18. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the J/ψ→pp¯ and ηc→pp¯ decays. The prompt ηc(1 S) production cross-section is determined to be σηc(1S)=1.26±0.11±0.08±0.14μb, where the last uncertainty includes that on the J/ ψ meson cross-section. The ratio of the branching fractions of b-hadron decays to the ηc(1 S) and J/ ψ states is measured to be Bb→ηcX/Bb→J/ψX=0.48±0.03±0.03±0.05, where the last uncertainty is due to those on the branching fractions of the J/ψ→pp¯ and ηc→pp¯ decays. The difference between the J/ ψ and ηc(1 S) masses is also determined to be 113.0±0.7±0.1MeV, which is the most precise single measurement of this quantity to date.

Abstract:

© 2020, CERN for the benefit of the LHCb Collaboration. The cross-sections of ψ(2 S) meson production in proton-proton collisions at s=13TeV are measured with a data sample collected by the LHCb detector corresponding to an integrated luminosity of 275pb-1. The production cross-sections for prompt ψ(2 S) mesons and those for ψ(2 S) mesons from b-hadron decays (ψ(2S)-from-b) are determined as functions of the transverse momentum, pT, and the rapidity, y, of the ψ(2 S) meson in the kinematic range 2<pT<20GeV/c and 2.0 < y< 4.5. The production cross-sections integrated over this kinematic region are σ(promptψ(2S),13TeV)=1.430±0.005(stat)±0.099(syst)μb,σ(ψ(2S)-from-b,13TeV)=0.426±0.002(stat)±0.030(syst)μb.A new measurement of ψ(2 S) production cross-sections in pp collisions at s=7TeV is also performed using data collected in 2011, corresponding to an integrated luminosity of 614pb-1. The integrated production cross-sections in the kinematic range 3.5<pT<14GeV/c and 2.0 < y< 4.5 are σ(promptψ(2S),7TeV)=0.471±0.001(stat)±0.025(syst)μb,σ(ψ(2S)-from-b,7TeV)=0.126±0.001(stat)±0.008(syst)μb.All results show reasonable agreement with theoretical calculations.

Abstract:

We report four narrow peaks in the Ξ_{b}^{0}K^{-} mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9  fb^{-1} recorded by the LHCb experiment. Referring to these states by their mass, the mass values are m[Ω_{b}(6316)^{-}]=6315.64±0.31±0.07±0.50  MeV, m[Ω_{b}(6330)^{-}]=6330.30±0.28±0.07±0.50  MeV, m[Ω_{b}(6340)^{-}]=6339.71±0.26±0.05±0.50  MeV, m[Ω_{b}(6350)^{-}]=6349.88±0.35±0.05±0.50  MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξ_{b}^{0} mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be Γ[Ω_{b}(6316)^{-}]<2.8  MeV, Γ[Ω_{b}(6330)^{-}]<3.1  MeV and Γ[Ω_{b}(6340)^{-}]<1.5  MeV. The natural width of the Ω_{b}(6350)^{-} peak is 1.4_{-0.8}^{+1.0}±0.1  MeV, which is 2.5σ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6σ to 7.2σ. After accounting for the look-elsewhere effect, the significances of the Ω_{b}(6316)^{-} and Ω_{b}(6330)^{-} peaks are reduced to 2.1σ and 2.6σ, respectively, while the two higher mass peaks exceed 5σ. The observed peaks are consistent with expectations for excited Ω_{b}^{-} resonances.