Multiplicity dependence of σψ(2S)/σJ/ψ in pp collisions at s \sqrt{s} = 13 TeV

Abstract The ratio of production cross-sections of ψ(2S) over J/ψ mesons as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy $$\sqrt{s}$$ s = 13 TeV is measured with a data sample collected by the LHCb detector, corresponding to an integrated luminosity of 658 pb−1. The ratio is measured for both prompt and non-prompt ψ(2S) and J/ψ mesons. When there is an overlap between the rapidity ranges over which multiplicity and charmonia production are measured, a multiplicity-dependent modification of the ratio is observed for prompt mesons. No significant multiplicity dependence is found when the ranges do not overlap. For non-prompt production, the ψ(2S)-to-J/ψ production ratio is roughly independent of multiplicity, irrespective of the rapidity range over which the multiplicity is measured. The results are compared to predictions of the co-mover model and agree well except in the low multiplicity region. The ratio of production cross-sections of ψ(2S) over J/ψ mesons are cross-checked with other measurements in di-lepton channels and found to be compatible.</jats:p

Curvature-bias corrections using a pseudomass method

Abstract Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy √(s)=13 TeV during 2016, 2017 and 2018. The biases are determined using Z→μ + μ - decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10-4 GeV-1 level, improves the Z→μ + μ - mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass.</jats:p

Momentum scale calibration of the LHCb spectrometer

Abstract For accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of 1.6 fb-1 collected during 2016 in pp running. The procedure uses large samples of J/ψ → μ + μ - and B+ → J/ψ K + decays and leads to a relative accuracy of 3 × 10-4 on the momentum scale.</jats:p