Study of the kinematic dependences of Λ 0b production in pp collisions and a measurement of the Λ 0b → Λ +c π − branching fraction

The kinematic dependences of the relative production rates, fΛ0b/fd, of Λ 0b baryons and B 0 mesons are measured using Λ 0b → Λ +c π − and B¯0 →D+π− decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb−1 at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, p T, and pseudorapidity, η, of the beauty hadron, in the studied kinematic region 1.5 < p T < 40 GeV/c and 2 < η < 5. Using a previous LHCb measurement of fΛ0b/fd in semileptonic decays, the branching fraction ℬ(Λ 0b → Λ +c π −) = (4.30 ± 0.03 + 0.12− 0.11 ± 0.26 ± 0.21) × 10− 3 is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of fΛ0b/fd and the fourth is due to the b B¯0 →D+π− branching fraction. This is the most precise measurement of a Λ 0b branching fraction to date.S

Measurement of forward Z → e+e− production s√s=8 TeV

A measurement of the cross-section for Z-boson production in the forward region of pp collisions at 8 TeV centre-of-mass energy is presented. The measurement is based on a sample of Z → e+e− decays reconstructed using the LHCb detector, corresponding to an integrated luminosity of 2.0 fb−1. The acceptance is defined by the requirements 2.0 20 GeV for the pseudorapidities and transverse momenta of the leptons. Their invariant mass is required to lie in the range 60-120 GeV. The cross-section is determined to beS

Measurement of indirect CP asymmetries in D0 → K−K+ and D0 → π−π+ decays using semileptonic B decays

Time-dependent CP asymmetries in the decay rates of the singly Cabibbo-suppressed decays D0 → K−K+ and D0 → π−π+ are measured in pp collision data corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment. The D0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial state as D0 or D¯0. The asymmetries in effective lifetimes between D0 and D¯0 decays, which are sensitive to indirect CP violation, are determined to be AΓ(K−K+)=(−0.134±0.077−0.026−0.034)%,AΓ(π−π+)=(−0.092±0.145−0.025−0.033)%, where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect CP violation in D0 decays.S

Evidence for the decay B+c→J/ψ3π+2π−

Evidence is presented for the decay B + c → J/ψ3π +2π − using proton-proton collision data, corresponding to an integrated luminosity of 3 fb−1 , collected with the LHCb detector. A signal yield of 32 ± 8 decays is found with a significance of 4.5 standard deviations. The ratio of the branching fraction of the B + c → J/ψ3π +2π − decay to that of the B+ c → J/ψπ+ decay is measured to be B (B+ c → J/ψ3π +2π −) B B + c → J/ψπ+ = 1.74 ± 0.44 ± 0.24, where the first uncertainty is statistical and the second is systematicS

Search for the decay D0→π+π−μ+μ−

A search for the D0→π+π−μ+μ− decay, where the muon pair does not originate from a resonance, is performed using proton–proton collision data corresponding to an integrated luminosity of 1.0 fb−1 recorded by the LHCb experiment at a centre-of-mass energy of 7 TeV. No signal is observed and an upper limit on the relative branching fraction with respect to the resonant decay mode D0→π+π− φ(→μ+μ− ), under the assumption of a phase-space model, is found to be B D0→π + π − μ + μ − /B D0→π + π − φ →μ + μ − < 0.96 at 90% confidence level. The upper limit on the absolute branching fraction is evaluated to be B(D0→π+π−μ+μ− ) < 5.5×10−7 at 90% confidence level. This is the most stringent to date.S

Measurement of the Ξ−b and Ω−b baryon lifetimes

Using a data sample of ppcollisions corresponding to an integrated luminosity of 3fb−1, the Ξ−band Ω−bbaryons are reconstructed in the Ξ−b→J/ψΞ−and Ω−b→J/ψΩ−decay modes and their lifetimes measured to be τ Ξ − b = 1.55+0.10 −0.09 (stat)±0.03 (syst) ps, τ Ω − b = 1.54+0.26 −0.21 (stat)± 0.05 (syst) ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictionsS

Effective lifetime measurements in the B0s→K+K−, B0→K+π−and B0s→π+K−decays

Measurements of the effective lifetimes in the B0s→K+K−, B0→K+π−and B0s→π+K−decays are presented using 1.0fb−1of ppcollision data collected at a centre-of-mass energy of 7TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. The measured effective lifetimes are τB0s→K+K−=1.407±0.016(stat)±0.007(syst)ps, τB0→K+π−=1.524±0.011(stat)±0.004(syst)ps, τB0s→π+K−=1.60±0.06(stat)±0.01(syst)ps. This is the most precise determination to date of the effective lifetime in the B0s→K+K−decay and provides constraints on contributions from physics beyond the Standard Model to the B0smixing phase and the width difference Γs.S

Evidence for the decay X(3872) →ψ(2S)γ

Evidence for the decay mode X(3872) →ψ(2S)γin B+→X(3872)K+decays is found with a sig-nificance of 4.4 standard deviations. The analysis is based on adata sample of proton–proton collisions, corresponding to an integrated luminosity of3fb−1, collected with the LHCb detector, at centre-of-mass energies of 7and8TeV. The ratio of the branching fraction of the X(3872) →ψ(2S)γdecay to that of the X(3872) →J/ψγdecay is measured to be B(X(3872)→ψ(2S)γ) B(X(3872)→J/ψγ) = 2.46± 0.64±0.29, where the first uncertainty is statistical and the second is systematic. The measured value does not support apureD¯ D∗molecular interpretation of the X(3872)state.S

Study of Υ production and cold nuclear matter effects in pPb collisions at √sNN = 5 TeV

Production of Υ mesons in proton-lead collisions at a nucleon-nucleon centre-of-mass energy √sNN = 5 TeV is studied with the LHCb detector. The analysis is based on a data sample corresponding to an integrated luminosity of 1.6 nb−1. The Υ mesons of transverse momenta up to 15 GeV/c are reconstructed in the dimuon decay mode. The rapidity coverage in the centre-of-mass system is 1.5 < y < 4.0 (forward region) and −5.0 < y < −2.5 (backward region). The forward-backward production ratio and the nuclear modification factor for Υ(1S) mesons are determined. The data are compatible with the predictions for a suppression of Υ(1S) production with respect to proton-proton collisions in the forward region, and an enhancement in the backward region. The suppression is found to be smaller than in the case of prompt J/ψ mesons.S

A study of CP violation in B± →DK± and B±→Dπ± decays with D→K0SK±π∓ final states

A first study of CP violation in the decay modes B±→[KS 0 K±π∓] D h±and B±→[KS 0 K∓ π±] D h±, where h labels a K or π meson and D labels a D 0 or D‾ 0 meson, is performed. The analysis uses the LHCb data set collected in pp collisions, corresponding to an integrated luminosity of 3 fb− 1. The analysis is sensitive to the CP-violating CKM phase γ through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of γ using other decay modesS