A search is performed for the charmless three-body decays of the Λ0b and Ξ0b baryons to the final states Λh+h′−, where h(′)=π or K. The analysis is based on a data sample, corresponding to an ...integrated luminosity of 3fb−1 of pp collisions, collected by the LHCb experiment. The Λ0b→ΛK+π− and Λ0b→ΛK+K− decays are observed for the first time and their branching fractions and CP asymmetry parameters are measured. Evidence is seen for the Λ0b→Λπ+π− decay and limits are set on the branching fractions of Ξ0b baryon decays to the Λh+h′− final states.
We perform a search for near-threshold Ξ0b resonances decaying to Ξ−bπ+ in a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb−1 collected by the LHCb ...experiment. We observe one resonant state, with the following properties:m(Ξ∗0b)−m(Ξ−b)−m(π+)=15.727±0.068(stat)±0.023(syst)MeV/c2,Γ(Ξ∗0b)=0.90±0.16(stat)±0.08(syst)MeV.This confirms the previous observation by the CMS collaboration. The state is consistent with the JP=3/2+ Ξ∗0b resonance expected in the quark model. This is the most precise determination of the mass and the first measurement of the natural width of this state. We have also measured the ratioσ(pp→Ξ∗0bX)B(Ξ∗0b→Ξ−bπ+)σ(pp→Ξ−bX)=0.27±0.03(stat)±0.01(syst).
The decay B¯¯¯0s→ψ(2S)K+π− is observed using a data set corresponding to an integrated luminosity of 3.0fb−1 collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 ...TeV. The branching fraction relative to the B0→ψ(2S)K+π− decay mode is measured to beB(B¯¯¯0s→ψ(2S)K+π−)B(B0→ψ(2S)K+π−)=5.38±0.36(stat)±0.22(syst)±0.31(fs/fd)%,where fs/fd indicates the uncertainty due to the ratio of probabilities for a b quark to hadronise into a B0s or B0 meson. Using an amplitude analysis, the fraction of decays proceeding via an intermediate K∗(892)0 meson is measured to be 0.645±0.049(stat)±0.049(syst) and its longitudinal polarisation fraction is 0.524±0.056(stat)±0.029(syst). The relative branching fraction for this component is determined to beB(B¯¯¯0s→ψ(2S)K∗(892)0)B(B0→ψ(2S)K∗(892)0)=5.58±0.57(stat)±0.40(syst)±0.32(fs/fd)%.In addition, the mass splitting between the B0s and B0 mesons is measured asM(B0s)−M(B0)=87.45±0.44(stat)±0.07(syst)MeV/c2.
Measurements are presented of electroweak boson production using data from pp collisions at a centre-of-mass energy of s√=8TeV. The analysis is based on an integrated luminosity of 2.0fb−1 recorded ...with the LHCb detector. The bosons are identified in the W→μν and Z→μ+μ− decay channels. The cross-sections are measured for muons in the pseudorapidity range 2.0<η<4.5, with transverse momenta pT>20GeV/c and, in the case of the Z boson, a dimuon mass within 60<Mμ+μ−<120GeV/c2. The results areσW+→μ+νσW−→μ−ν¯σZ→μ+μ−=1093.6±2.1±7.2±10.9±12.7pb,=818.4±1.9±5.0±7.0±9.5pb,=95.0±0.3±0.7±1.1±1.1pb,where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the W and Z boson cross-sections with centre-of-mass energy is studied using previously reported measurements with 1.0fb−1 of data at 7TeV. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.
The branching fraction ratio R(D∗)≡B(B¯¯¯0→D∗+τ−ν¯τ)/B(B¯¯¯0→D∗+μ−ν¯μ) is measured using a sample of proton-proton collision data corresponding to 3.0\invfb of integrated luminosity recorded by the ...LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ−→μ−ν¯μντ. The semitauonic decay is sensitive to contributions from non-Standard-Model particles that preferentially couple to the third generation of fermions, in particular Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate B¯¯¯0 decays gives R(D∗)=0.336±0.027(stat)±0.030(syst). This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the Standard Model.
The first observation of the B 0 s → η ′ η ′ decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0 fb − 1 of integrated luminosity collected with the ...LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be 3.31 ± 0.64 ( stat ) ± 0.28 ( syst ) ± 0.12 ( norm ) × 10 − 5 , where the third uncertainty comes from the B ± → η ′ K ± branching fraction that is used as a normalization. In addition, the charge asymmetries of B ± → η ′ K ± and B ± → ϕ K ± , which are control channels, are measured to be ( − 0.2 ± 1.3 ) % and ( + 1.7 ± 1.3 ) % , respectively. All results are consistent with theoretical expectations.
The difference in total widths between the B+c and B+ mesons is measured using 3.0fb−1 of data collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the ...LHC. Through the study of the time evolution of B+c→J/ψπ+ and B+→J/ψK+ decays, the width difference is measured to beΔΓ≡ΓB+c−ΓB+=4.46±0.14±0.07mm−1c,where the first uncertainty is statistical and the second systematic. The known lifetime of the B+ meson is used to convert this to a precise measurement of the B+c lifetime,τB+c=513.4±11.0±5.7fs,where the first uncertainty is statistical and the second systematic.
Measurements are presented of the C P violation observables S and C in the decays of B 0 and ¯ B 0 mesons to the J / ψ K 0 S final state. The data sample corresponds to an integrated luminosity of ...3.0 fb − 1 collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B 0 and ¯ B 0 decays. The analysis of the time evolution of these decays yields S = 0.731 ± 0.035 ( stat ) ± 0.020 ( syst ) and C = − 0.038 ± 0.032 ( stat ) ± 0.005 ( syst ) . In the standard model, S equals sin ( 2 β ) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.
The production of $J/\psi$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is studied with the LHCb detector. Cross-section measurements are performed as a function ...of the transverse momentum $p_\mathrm{T}$ and the rapidity $y$ of the $J/\psi$ meson in the region $p_\mathrm{T}<14 \mathrm{GeV}/c$ and $2.0<y<4.5$, for both prompt $J/\psi$ mesons and $J/\psi$ mesons from $b$-hadron decays. The production cross-sections integrated over the kinematic coverage are $15.30\pm 0.03\pm 0.86$ $\mu$b for prompt $J/\psi$ and $2.34\pm 0.01\pm 0.13$ $\mu$b for $J/\psi$ from $b$-hadron decays, assuming zero polarization of the $J/\psi$ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for $J/\psi$ mesons from $b$-hadron decays is used to extrapolate to a total $b\bar{b}$ cross-section. The ratios of the cross-sections with respect to $\sqrt{s}=8$ TeV are also determined.
A search for the rare decays B0s→π+π−μ+μ− and B0→π+π−μ+μ− is performed in a data set corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb detector in proton-proton collisions ...at centre-of-mass energies of 7 and 8 TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5-1.3 GeV/c2 and with muon pairs that do not originate from a resonance are considered. The first observation of the decay B0s→π+π−μ+μ− and the first evidence of the decay B0→π+π−μ+μ− are obtained and the branching fractions are measured to be B(B0s→π+π−μ+μ−)=(8.6±1.5(stat)±0.7(syst)±0.7(norm))×10−8 and B(B0→π+π−μ+μ−)=(2.11±0.51(stat)±0.15(syst)±0.16(norm))×10−8, where the third uncertainty is due to the branching fraction of the decay B0→J/ψ(→μ+μ−)K∗(890)0(→K+π−), used as a normalisation.
PDF
