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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 first 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.
    Free, publicly-accessible full text available July 1, 2023
  2. Abstract A search is performed for massive long-lived particles (LLPs) decaying semileptonically into a muon and two quarks. Two kinds of LLP production processes were considered. In the first, a Higgs-like boson with mass from 30 to 200 $$\text {\,GeV\!/}c^2$$ \,GeV\!/ c 2 is produced by gluon fusion and decays into two LLPs. The analysis covers LLP mass values from 10 $$\text {\,GeV\!/}c^2$$ \,GeV\!/ c 2 up to about one half the Higgs-like boson mass. The second LLP production mode is directly from quark interactions, with LLP masses from 10 to 90 $$\text {\,GeV\!/}c^2$$ \,GeV\!/ c 2 . The LLP lifetimes considered range from 5 to 200 ps. This study uses LHCb data collected from proton-proton collisions at $$\sqrt{s} = 13\text {\,TeV} $$ s = 13 \,TeV , corresponding to an integrated luminosity of 5.4 $$\text {\,fb} ^{-1}$$ \,fb - 1 . No evidence of these long-lived states has been observed, and upper limits on the production cross-section times branching ratio have been set for each model considered.
    Free, publicly-accessible full text available April 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 meson 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.
    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 MeV , 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.
    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 − γ ) < 1 . 3 × 10 − 4 at 95% confidence level is obtained.
    Free, publicly-accessible full text available January 1, 2023