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+νμ decay modes with 0.37 fb−1 of data collected in pp collisions at 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 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 p T and rapidity y in the fiducial region p T ∈ [0; 14] GeV/c and y ∈ [2.0; 4 cross-section and fraction of J/ψ from b-hadron decays are also measured in the same p T 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 ± 1.40−2.20 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.

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Using 34.7 pb −1 of data collected with the LHCb detector, the inclusive production of the X(3872) meson in pp collisions at √ s = 7 TeV is observed for the first time. Candidates are selected in the X(3872) → J /ψπ + π − decay mode, and used to measure σ pp → X(3872) + anything B X(3872) → J /ψπ + π − = 5.4 ± 1.3 (stat) ± 0.8 (syst) nb, where σ (pp → X(3872) + anything) is the inclusive production cross section of X(3872) mesons with rapidity in the range 2.5-4.5 and transverse momentum in the range 5-20 GeV/c. In addition the masses of both the X(3872) and ψ(2S) mesons, reconstructed in the J /ψπ + π − final state, are measured to be m X(3872) = 3871.95 ± 0.48 (stat) ± 0.12 (syst) MeV/c 2 and m ψ(2S) = 3686.12 ± 0.06 (stat) ± 0.10 (syst) MeV/c 2 .

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