[en] 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. (paper)

[en] A new algorithm for the determination of the initial flavour of B ⁰_s mesons is presented. The algorithm is based on two neural networks and exploits the b hadron production mechanism at a hadron collider. The first network is trained to select charged kaons produced in association with the B ⁰_s meson. The second network combines the kaon charges to assign the B ⁰_s flavour and estimates the probability of a wrong assignment. The algorithm is calibrated using data corresponding to an integrated luminosity of 3 fb⁻¹ collected by the LHCb experiment in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the B ⁰_s – B-bar ⁰_s flavour oscillations in B ⁰_s  →  D ⁻_s π⁺ decays, and by analysing flavour-specific B ^*_s2(5840)⁰ →  B ⁺ K ⁻ decays. The tagging power measured in B ⁰_s  →  D ⁻_s π⁺ decays is found to be (1.80 ± 0.19 (stat) ± 0.18 (syst))%, which is an improvement of about 50% compared to a similar algorithm previously used in the LHCb experiment.

[en] The single electron track-reconstruction efficiency is calibrated using a sample corresponding to 1.3 fb⁻¹ of pp collision data recorded with the LHCb detector in 2017. This measurement exploits B⁺→ J/ψ(e⁺e⁻)K⁺ decays, where one of the electrons is fully reconstructed and paired with the kaon, while the other electron is reconstructed using only the information of the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow the B meson mass to be reconstructed and the signal to be well separated from backgrounds. This in turn allows the electron reconstruction efficiency to be measured by matching the partial track segment found in the vertex detector to tracks found by LHCb's regular reconstruction algorithms. The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. These correction factors allow LHCb to measure branching fractions involving single electrons with a systematic uncertainty below 1%.

[en] A search is performed for the central exclusive production of pairs of charmonia produced in proton-proton collisions. Using data corresponding to an integrated luminosity of 3fb"−"1 collected at centre-of-mass energies of 7 and 8 TeV, J/ψJ/ψ and J/ψψ(2S) pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges (−3.5,−1.5) and (1.5,5.0). Searches are also performed for pairs of P-wave charmonia and limits are set on their production. The cross-sections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measured, where the upper limits are set at the 90% confidence level. The measured J/ψJ/ψ and J/ψψ(2S) cross-sections are consistent with theoretical expectations. (paper)