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

A measurement of the inclusive Z → ττ cross-section in pp collisions at √s =7 is presented based on a dataset of 1.0 fb[superscript −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[superscript 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[subscript 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.National Science Foundation (U.S.

Precision measurement of the B0s-B¯0s oscillation frequency with the decay B0s → D−sπ+

A key ingredient to searches for physics beyond the Standard Model in B0s mixing phenomena is the measurement of the B0s– ${{\overline{ {\mathrm {B}}}{}}^0_{\mathrm { s}}}$ oscillation frequency, which is equivalent to the mass difference Δms of the B0s mass eigenstates. Using the world's largest B0s meson sample accumulated in a dataset, corresponding to an integrated luminosity of 1.0 fb−1, collected by the LHCb experiment at the CERN LHC in 2011, a measurement of Δms is presented. A total of about 34 000 B0s → D−sπ+ signal decays are reconstructed, with an average decay time resolution of 44 fs. The oscillation frequency is measured to be Δms = 17.768 ± 0.023 (stat) ± 0.006 (syst) ps−1, which is the most precise measurement to date

Differential branching fraction and angular analysis of the decay B s0 → φμ + μ -

The determination of the differential branching fraction and the first angular analysis of the decay Bs0 → φμ + μ - are presented using data, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment at √s=7 TeV. The differential branching fraction is determined in bins of q 2, the invariant dimuon mass squared. Integration over the full q 2 range yields a total branching fraction of B (Bs0 → φμ + μ -(7.07 -0.59+0.64± 0.71± 0.71) × 10 -7, where the first uncertainty is statistical, the second systematic, and the third originates from the branching fraction of the normalisation channel. An angular analysis is performed to determine the angular observables F L, S 3, A 6, and A 9. The observables are consistent with Standard Model expectations. [Figure not available: see fulltext.] © 2013 CERN for the benefit of the LHCb collaboration

Updated measurements of exclusive J/ψ and ψ(2S) production cross-sections in pp collisions at √s = 7 TeV

The differential cross-section as a function of rapidity has been measured for the exclusive production of J/ψ and ψ(2S) mesons in proton–proton collisions at √s = 7 TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pb−1. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects

First evidence for the two-body charmless baryonic decay B0 → pp̄

The results of a search for the rare two-body charmless baryonic decays B0 → pp̄ and B0s → pp̄ are reported. The analysis uses a data sample, corresponding to an integrated luminosity of 0.9 fb-1, of pp collision data collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. An excess of B0 → pp̄ candidates with respect to background expectations is seen with a statistical significance of 3.3 standard deviations. This is the first evidence for a two-body charmless baryonic B0 decay. No significant B0s → pp̄ signal is observed, leading to an improvement of three orders of magnitude over previous bounds. If the excess events are interpreted as signal, the 68.3% confidence level intervals on the branching fractions are (Equation) where the first uncertainty is statistical and the second is systematic

Observation of B_{c}^{+}→J/ψD_{s}^{+} and B_{c}^{+}→J/ψD_{s}^{*+} decays

The decays B+c→J/ψD+s and B+c→J/ψD*+s are observed for the first time using a dataset, corresponding to an integrated luminosity of 3  fb−1, collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of s√=7 and 8 TeV. The statistical significance for both signals is in excess of 9 standard deviations. The following ratios of branching fractions are measured to be B(B+c→J/ψD+s)B(B+c→J/ψπ+)=2.90±0.57±0.24, B(B+c→J/ψD*+s)B(B+c→J/ψD+s)=2.37±0.56±0.10, where the first uncertainties are statistical and the second systematic. The mass of the B+c meson is measured to be mB+c=6276.28±1.44(stat)±0.36(syst)  MeV/c2, using the B+c→J/ψD+s decay mode

A search for rare B → Dμ+μ− decays

A search for rare B→Dμ+μ− decays is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. No significant signals are observed in the non-resonant μ+μ− modes, and upper limits of B(B0→D ̄ ̄ ̄ ̄0μ+μ−)<5.1×10−8, B(B+→D+sμ+μ−)<3.2×10−8, B(B0s→D ̄ ̄ ̄ ̄0μ+μ−)<1.6×10−7 and fc/fu⋅B(B+c→D+sμ+μ−)<9.6×10−8 are set at the 95\% confidence level, where fc and fu are the fragmentation fractions of a B meson with a c and u quark respectively in proton-proton collisions. Each result is either the first such measurement or an improvement by three orders of magnitude on an existing limit. Separate upper limits are calculated when the muon pair originates from a J/ψ→μ+μ− decay. The branching fraction of B+c→D+sJ/ψ multiplied by the fragmentation-fraction ratio is measured to be fc/fu⋅B(B+c→D+sJ/ψ)=(1.63±0.15±0.13)×10−5, where the first uncertainty is statistical and the second systematic

Observation of Two New Excited Ξb0 States Decaying to Λb0 K-π+

Two narrow resonant states are observed in the Λb0K-π+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6 fb-1. The minimal quark content of the Λb0K-π+ system indicates that these are excited Ξb0 baryons. The masses of the Ξb(6327)0 and Ξb(6333)0 states are m[Ξb(6327)0]=6327.28-0.21+0.23±0.12±0.24 and m[Ξb(6333)0]=6332.69-0.18+0.17±0.03±0.22 MeV, respectively, with a mass splitting of Δm=5.41-0.27+0.26±0.12 MeV, where the uncertainties are statistical, systematic, and due to the Λb0 mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Γ[Ξb(6327)0]<2.20(2.56) and Γ[Ξb(6333)0]<1.60(1.92) MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Ξb0 resonances

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

Studies of beauty baryon decays to D0ph− and Λ+ch− final states

Decays of beauty baryons to the D0ph− and Λ+ch− final states (where h indicates a pion or a kaon) are studied using a data sample of pp collisions, corresponding to an integrated luminosity of 1.0  fb−1, collected by the LHCb detector. The Cabibbo-suppressed decays Λ0b→D0pK− and Λ0b→Λ+cK− are observed, and their branching fractions are measured with respect to the decays Λ0b→D0pπ− and Λ0b→Λ+cπ−. In addition, the first observation is reported of the decay of the neutral beauty-strange baryon Ξ0b to the D0pK− final state, and a measurement of the Ξ0b mass is performed. Evidence of the Ξ0b→Λ+cK− decay is also reported