Prompt and nonprompt J/ψ production and nuclear modification in pPb collisions at √sNN=8.16TeV
Physics Letters B Elsevier 774:10 (2017) 159-178
Abstract:
he production of J/ψ mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair √sNN =8.16 TeV with the LHCb detector at the LHC. The double differential cross-sections of prompt and nonprompt J/ψ production are measured as a function of the J/ψ transverse momentum and rapidity in the nucleon–nucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.Study of charmonium production in b-hadron decays and first evidence for the decay Bs0 → ϕ ϕ ϕ
European Physical Journal C Springer 77 (2017)
Abstract:
Using decays to ϕ-meson pairs, the inclusive production of charmonium states in b-hadron decays is studied with pp collision data corresponding to an integrated luminosity of 3.0fb-1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting by BC≡B(b→CX)×B(C) the inclusive branching fraction of a b hadron to a charmonium state C that decays into a pair of ϕ mesons, ratios RC2C1≡BC1/BC2 are determined as Rηc(1S)χc0=0.147±0.023±0.011, Rηc(1S)χc1=0.073±0.016±0.006, Rηc(1S)χc2=0.081±0.013±0.005, Rχc0χc1=0.50±0.11±0.01, Rχc0χc2=0.56±0.10±0.01 and Rηc(1S)ηc(2S)=0.040±0.011±0.004. Here and below the first uncertainties are statistical and the second systematic. Upper limits at 90% confidence level for the inclusive production of X(3872), X(3915) and χ c 2 (2 P) states are obtained as Rχc1X(3872) < 0.34, Rχc0X(3915) < 0.12 and Rχc2χc2(2P) < 0.16. Differential cross-sections as a function of transverse momentum are measured for the η c (1 S) and χ c states. The branching fraction of the decay Bs0 is measured for the first time, B(Bs0)=(2.15±0.54±0.28±0.21B)×10-6. Here the third uncertainty is due to the branching fraction of the decay Bs0, which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse ϕ polarization is observed. The measurements allow the determination of the ratio of the branching fractions for the η c (1 S) decays to ϕϕ and pp¯ as B(ηc(1S))/B(ηc(1S)→pp¯)=1.79±0.14±0.32.Measurement of B_{s}^{0} and D_{s}^{-} Meson Lifetimes.
Physical review letters 119:10 (2017) 101801
Abstract:
We report on a measurement of the flavor-specific B_{s}^{0} lifetime and of the D_{s}^{-} lifetime using proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to 3.0 fb^{-1} of integrated luminosity. Approximately 407 000 B_{s}^{0}→D_{s}^{(*)-}μ^{+}ν_{μ} decays are partially reconstructed in the K^{+}K^{-}π^{-}μ^{+} final state. The B_{s}^{0} and D_{s}^{-} natural widths are determined using, as a reference, kinematically similar B^{0}→D^{(*)-}μ^{+}ν_{μ} decays reconstructed in the same final state. The resulting differences between widths of B_{s}^{0} and B^{0} mesons and of D_{s}^{-} and D^{-} mesons are Δ_{Γ}(B)=-0.0115±0.0053(stat)±0.0041(syst) ps^{-1} and Δ_{Γ}(D)=1.0131±0.0117(stat)±0.0065(syst) ps^{-1}, respectively. Combined with the known B^{0} and D^{-} lifetimes, these yield the flavor-specific B_{s}^{0} lifetime, τ_{B_{s}^{0}}^{fs}=1.547±0.013(stat)±0.010(syst)±0.004(τ_{B}) ps and the D_{s}^{-} lifetime, τ_{D_{s}^{-}}=0.5064±0.0030(stat)±0.0017(syst)±0.0017(τ_{D}) ps. The last uncertainties originate from the limited knowledge of the B^{0} and D^{-} lifetimes. The results improve upon current determinations.Test of lepton universality with B 0 → K *0 ℓ + ℓ − decays
Journal of High Energy Physics Springer 2017:8 (2017) 055
Abstract:
A test of lepton universality, performed by measuring the ratio of the branching fractions of the B 0 → K *0 μ + μ − and B 0 → K *0 e + e − decays, RK*0, is presented. The K *0 meson is reconstructed in the final state K + π − , which is required to have an invariant mass within 100 MeV/c 2 of the known K * (892) 0 mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb −1 , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q 2 , to be (Formula presented.) The corresponding 95.4% confidence level intervals are [0.52, 0.89] and [0.53, 0.94] . The results, which represent the most precise measurements of RK*0 to date, are compatible with the Standard Model expectations at the level of 2.1–2.3 and 2.4–2.5 standard deviations in the two q 2 regions, respectively.[Figure not available: see fulltext.].Observation of the Decays Λ0b→χc1pK− and Λ0b→χc2pK−
Physical Review Letters American Physical Society 119:6 (2017) 062001
Abstract:
The first observation of the decays $Λ_{b}^{0}→χ_{c1}pK^{-}$ and $Λ_{b}^{0}→χ_{c2}pK^{-}$ is reported using a data sample corresponding to an integrated luminosity of $3.0 fb^{-1}$, collected by the LHCb experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured:$B(Λ_{b}^{0}→χ_{c1}pK^{-})/B(Λ_{b}^{0}→J/ψpK^{-})=0.242±0.014±0.013±0.009,$ $B(Λ_{b}^{0}→χ_{c2}pK^{-})/B(Λ_{b}^{0}→J/ψpK^{-})=0.248±0.020±0.014±0.009,$ $B(Λ_{b}^{0}→χ_{c2}pK^{-})/B(Λ_{b}^{0}→χ_{c1}pK^{-})=1.02±0.10±0.02±0.05,$
where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the $χ_{c1}→J/ψγ$ and $χ_{c2}→J/ψγ$ decays. Using both decay modes, the mass of the $Λ_{b}^{0}$ baryon is also measured to be $m_{Λ_{b}^{0}}=5619.44±0.28±0.26 MeV/c^{2}$, where the first and second uncertainties are statistical and systematic, respectively.