A study of the Z production cross-section in pp collisions at s√=7 TeV using tau final states

A measurement of the inclusive Z → ττ cross-section in pp collisions at s√=7TeV is presented based on a dataset of 1.0 fb−1 collected by the LHCb detector. Candidates for Z → τ τ decays are identified through reconstructed final states with two muons, a muon and an electron, a muon and a hadron, or an electron and a hadron. The production cross-section for Z bosons, with invariant mass between 60 and 120 GeV/c 2, which decay to τ leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5, is measured to be σ pp→Z→ττ = 71.4 ± 3.5 ± 2.8 ± 2.5 pb; the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the integrated luminosity. The ratio of the cross-sections for Z → τ τ to Z → μμ is determined to be 0.93 ± 0.09, where the uncertainty is the combination of statistical, systematic, and luminosity uncertainties of the two measurements

Measurement of relative branching fractions of B decays to ψ(2S) and J/ψ mesons

The relative rates of B-meson decays into J/ψ and ψ(2S) mesons are measured for the three decay modes in pp collisions recorded with the LHCb detector. The ratios of branching fractions ( B) are measured to be where the third uncertainty is from the ratio of the ψ(2S) and J/ψ branching fractions to μ + μ −

Search for the rare decay KS→μ+μ−

A search for the decay K0S→μ+μ− is performed, based on a data sample of 1.0 fb−1 of pp collisions at s√=7TeV collected by the LHCb experiment at the Large Hadron Collider. The observed number of candidates is consistent with the background-only hypothesis, yielding an upper limit of B(K0S→μ+μ−) < 11(9) × 10−9 at 95 (90)% confidence level. This limit is a factor of thirty below the previous measurement

Determination of fs/fd for 7 TeV pp Collisions and Measurement of the B0→D−K+ Branching Fraction

The relative abundance of the three decay modes B 0 → D − K + , B 0 → D − π + , and B 0 s → D − s π + produced in 7 TeV p p collisions at the LHC is determined from data corresponding to an integrated luminosity of 35     pb − 1 . The branching fraction of B 0 → D − K + is found to be B ( B 0 → D − K + ) = ( 2.01 ± 0.18 stat ± 0.14 syst ) × 10 − 4 . The ratio of fragmentation fractions f s / f d is determined through the relative abundance of B 0 s → D − s π + to B 0 → D − K + and B 0 → D − π + , leading to f s / f d = 0.253 ± 0.017 ± 0.017 ± 0.020 , where the uncertainties are statistical, systematic, and theoretical, respectively

Measurement of V 0 production ratios in pp collisions at s √ = 0.9 and 7 TeV

The Λ¯/Λ and Λ¯/K0S production ratios are measured by the LHCb detector from 0.3 nb−1 of pp collisions delivered by the LHC at s√=0.9 TeV and 1.8 nb−1 at s√=7 TeV. Both ratios are presented as a function of transverse momentum, p T, and rapidity, y, in the ranges 0.15 < p T < 2.50 GeV/c and 2.0 < y < 4.5. Results at the two energies are in good agreement as a function of rapidity loss, ∆y = y beam − y, and are consistent with previous measurements. The ratio Λ¯/Λ , measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted in simulation, particularly at high rapidity. The ratio Λ¯/K0S , measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected

First observation of the decays ¯¯¯B0(s)→D+sK−π+π− and ¯¯¯B0s→Ds1(2536)+π−

The first observation of the decays ¯¯¯ B 0 s → D + s K − π + π − and ¯¯¯ B 0 → D + s K − π + π − are reported using an integrated luminosity of 1.0     fb − 1 recorded by the LHCb experiment. The branching fractions, normalized with respect to ¯¯¯ B 0 s → D + s π − π + π − and ¯¯¯ B 0 s → D + s K − π + π − , respectively, are measured to be B ( ¯¯¯ B 0 s → D + s K − π + π − ) B ( ¯¯¯ B 0 s → D + s π − π + π − ) = ( 5.2 ± 0.5 ± 0.3 ) × 10 − 2 and B ( ¯¯¯ B 0 → D + s K − π + π − ) B ( ¯¯¯ B 0 s → D + s K − π + π − ) = 0.54 ± 0.07 ± 0.07 , where the first uncertainty is statistical and the second is systematic. The ¯¯¯ B 0 s → D + s K − π + π − decay is of particular interest as it can be used to measure the weak phase γ . First observation of the ¯¯¯ B 0 s → D s 1 ( 2536 ) + π − , D + s 1 → D + s π − π + decay is also presented, and its branching fraction relative to ¯¯¯ B 0 s → D + s π − π + π − is found to be B ( ¯¯¯ B 0 s → D s 1 ( 2536 ) + π − , D + s 1 → D + s π − π + ) B ( ¯¯¯ B 0 s → D + s π − π + π − ) = ( 4.0 ± 1.0 ± 0.4 ) × 10 −

Measurement of V 0 production ratios in pp collisions at s √ = 0.9 and 7 TeV

The Λ¯/Λ and Λ¯/K0S production ratios are measured by the LHCb detector from 0.3 nb−1 of pp collisions delivered by the LHC at s√=0.9 TeV and 1.8 nb−1 at s√=7 TeV. Both ratios are presented as a function of transverse momentum, p T, and rapidity, y, in the ranges 0.15 < p T < 2.50 GeV/c and 2.0 < y < 4.5. Results at the two energies are in good agreement as a function of rapidity loss, ∆y = y beam − y, and are consistent with previous measurements. The ratio Λ¯/Λ , measuring the transport of baryon number from the collision into the detector, is smaller in data than predicted in simulation, particularly at high rapidity. The ratio Λ¯/K0S , measuring the baryon-to-meson suppression in strange quark hadronisation, is significantly larger than expected

Search for CP violation in D+→K−K+π+ decays

A model-independent search for direct C P violation in the Cabibbo-suppressed decay D + → K − K + π + in a sample of approximately 370 000 decays is carried out. The data were collected by the LHCb experiment in 2010 and correspond to an integrated luminosity of 35     pb − 1 . The normalized Dalitz plot distributions for D + and D − are compared using four different binning schemes that are sensitive to different manifestations of C P violation. No evidence for C P asymmetry is found

Measurement of the cross-section for Z → e+e- production in pp collisions at s√=7 TeV

A measurement of the cross-section for pp → Z → e+e− is presented using data at s√=7 TeV corresponding to an integrated luminosity of 0.94 fb−1. The process is measured within the kinematic acceptance p T > 20 GeV/c and 2 120 GeV/c 2. The cross-section is determined to be $\sigma \left( {\mathrm{pp}\to \mathrm{Z}\to {{\mathrm{e}}^{+}}{{\mathrm{e}}^{-}}} \right)=76.0\pm 0.8\pm 2.0\pm 2.6\;\mathrm{pb}$ where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD

Measurement of the cross-section for Z → e+e- production in pp collisions at s√=7 TeV

A measurement of the cross-section for pp → Z → e+e− is presented using data at s√=7 TeV corresponding to an integrated luminosity of 0.94 fb−1. The process is measured within the kinematic acceptance p T > 20 GeV/c and 2 120 GeV/c 2. The cross-section is determined to be $\sigma \left( {\mathrm{pp}\to \mathrm{Z}\to {{\mathrm{e}}^{+}}{{\mathrm{e}}^{-}}} \right)=76.0\pm 0.8\pm 2.0\pm 2.6\;\mathrm{pb}$ where the first uncertainty is statistical, the second is systematic and the third is the uncertainty in the luminosity. The measurement is performed as a function of Z rapidity and as a function of an angular variable which is closely related to the Z transverse momentum. The results are compared with previous LHCb measurements and with theoretical predictions from QCD