The production of J/ψ mesons in proton-proton collisions at √S = 7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/ψ production is measured as a function of the J/ψ transverse momentum pT and rapidity y in the fiducial region pT ∈ [0; 14] GeV/c and y ∈ [2.0; 4.5]. The differential cross-section and fraction of J/ψ from b-hadron decays are also measured in the same pT and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2 pb^&-1. The measured cross-sections integrated over the fiducial region are 10.52 ± 0.04 ± 1.40^+1.64 &-2.20 μb for prompt J/ψ production and 1.14 ± 0.01 ± 0.16 μb for J/ψ from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/ψ production cross-section is obtained assuming no J/ψ polarisation and the third error indicates the acceptance uncertainty due to this assumption.

The B s0→J/ψK S0 branching fraction is measured in a data sample corresponding to 0.41fb -1 of integrated luminosity collected with the LHCb detector at the LHC. This channel is sensitive to the penguin contributions affecting the sin2β measurement from B 0→J/ψK S0. The time-integrated branching fraction is measured to be B(B S0→J/ψK S0)=(1.83±0.28)×10 -5. This is the most precise measurement to date. © 2012 CERN.

Charged particle production in proton-proton collisions is studied with the LHCb detector at a centre-of-mass energy of √s = 7 TeV in different intervals of pseudorapidity η. Charged particles are reconstructed close to the interaction region in the vertex detector, which provides high reconstruction efficiency in the η ranges −2.5 < η <−2.0 and 2.0 < η < 4.5. The data were taken with a minimum bias trigger, only requiring one or more reconstructed tracks in the vertex detector. By selecting an event sample with at least one track with a transverse momentum greater than 1 GeV/c a hard QCD subsample is investigated. Several event generators are compared with the data; none are able to describe fully the multiplicity distributions or the charged particle density distribution as a function of η. In general, the models underestimate charged particle production.

The calibration and performance of the opposite-side flavour tagging algorithms used for the measurements of time-dependent asymmetries at the LHCb experiment are described. The algorithms have been developed using simulated events and optimized and calibrated with B⁺→J/ψK⁺, B⁰→J/ψK^∗0 and B⁰→D^∗-μ⁺ν_μ decay modes with 0.37 fb^-1 of data collected in pp collisions at [Formula: see text] during the 2011 physics run. The opposite-side tagging power is determined in the B⁺→J/ψK⁺ channel to be (2.10±0.08±0.24) %, where the first uncertainty is statistical and the second is systematic.

The production of ϒ(1S), ϒ(2S) and ϒ(3S) mesons in proton-proton collisions at the centre-of-mass energy of [Formula: see text] is studied with the LHCb detector. The analysis is based on a data sample of 25 pb^-1 collected at the Large Hadron Collider. The ϒ mesons are reconstructed in the decay mode ϒ→μ⁺μ^- and the signal yields are extracted from a fit to the μ⁺μ^- invariant mass distributions. The differential production cross-sections times dimuon branching fractions are measured as a function of the ϒ transverse momentum p_T and rapidity y, over the range p_T <15 GeV/c and 2.0<y<4.5. The cross-sections times branching fractions, integrated over these kinematic ranges, are measured to be [Formula: see text] where the first uncertainty is statistical, the second systematic and the third is due to the unknown polarisation of the three ϒ states.

The differential cross-section for the inclusive production of ψ(2S) mesons in pp collisions at [Formula: see text] has been measured with the LHCb detector. The data sample corresponds to an integrated luminosity of 36 pb^-1. The ψ(2S) mesons are reconstructed in the decay channels ψ(2S)→μ⁺μ^- and ψ(2S)→J/ψπ⁺π^-, with the J/ψ meson decaying into two muons. Results are presented both for promptly produced ψ(2S) mesons and for those originating from b-hadron decays. In the kinematic range p_T(ψ(2S))≤16 GeV/c and 2<y(ψ(2S))≤4.5 we measure [Formula: see text] where the last uncertainty on the prompt cross-section is due to the unknown ψ(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/ψ measurements we determine the inclusive branching fraction [Formula: see text] where the last uncertainty is due to the [Formula: see text], [Formula: see text] and [Formula: see text] branching fraction uncertainties.