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  1. A bstract Coherent production of J/ψ mesons is studied in ultraperipheral lead-lead collisions at a nucleon-nucleon centre-of-mass energy of 5 TeV, using a data sample collected by the LHCb experiment corresponding to an integrated luminosity of about 10 μb −1 . The J/ψ mesons are reconstructed in the dimuon final state and are required to have transverse momentum below 1 GeV. The cross-section within the rapidity range of 2 . 0 < y < 4 . 5 is measured to be 4 . 45 ± 0 . 24 ± 0 . 18 ± 0 . 58 mb, where the firstmore »uncertainty is statistical, the second systematic and the third originates from the luminosity determination. The cross-section is also measured in J/ψ rapidity intervals. The results are compared to predictions from phenomenological models.« less
    Free, publicly-accessible full text available July 1, 2023
  2. Abstract The centrality of heavy-ion collisions is directly related to the created medium in these interactions. A procedure to determine the centrality of collisions with the LHCb detector is implemented for lead-lead collisions at √ s NN = 5 TeV and lead-neon fixed-target collisions at √ s NN = 69 GeV. The energy deposits in the electromagnetic calorimeter are used to determine and define the centrality classes. The correspondence between the number of participants and the centrality for the lead-lead collisions is in good agreement with the correspondence found in other experiments, and the centrality measurements for the lead-neon collisionsmore »presented here are performed for the first time in fixed-target collisions at the LHC.« less
    Free, publicly-accessible full text available May 1, 2023
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  5. Abstract The standard model of particle physics currently provides our best description of fundamental particles and their interactions. The theory predicts that the different charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton–proton collision data collected with the LHCb detector at CERN’s Large Hadron Collider. The measurements are of processes in which a beauty mesonmore »transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. If confirmed by future measurements, this violation of lepton universality would imply physics beyond the standard model, such as a new fundamental interaction between quarks and leptons.« less
    Free, publicly-accessible full text available March 1, 2023
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  9. A bstract The W boson mass is measured using proton-proton collision data at $$ \sqrt{s} $$ s = 13 TeV corresponding to an integrated luminosity of 1.7 fb − 1 recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon q/p T distribution of a sample of W → μν decays and the ϕ * distribution of a sample of Z → μμ decays the W boson mass is determined to be $$ {m}_w=80354\pm {23}_{\mathrm{stat}}\pm {10}_{\mathrm{exp}}\pm {17}_{\mathrm{theory}}\pm {9}_{\mathrm{PDF}}\mathrm{MeV}, $$ m w = 80354 ± 23 stat ± 10 exp ± 17 theory ± 9 PDF MeVmore », where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.« less
    Free, publicly-accessible full text available January 1, 2023
  10. A bstract The first search for the rare radiative decay $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − γ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb − 1 . The $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − J/ψ channel is used as normalization. No $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − γ signal is found and an upper limit of $$ \mathcal{B} $$ B ( $$ {\Xi}_b^{-} $$ Ξ b − → Ξ − γmore ») < 1 . 3 × 10 − 4 at 95% confidence level is obtained.« less
    Free, publicly-accessible full text available January 1, 2023