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Mesons comprising a beauty quark and strange quark can oscillate between particle ( B s 0 ) and antiparticle ( B ¯ s 0 ) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, Δ m s . Here we present a measurement of Δ m s using B s 0 → D s − π + decays produced in proton–proton collisions collected with the LHCb detector at the Large Hadron Collider. The oscillation frequency is found to be Δ m s  = 17.7683 ± 0.0051 ± 0.0032 ps −1 , where the first uncertainty is statistical and the second is systematic. This measurement improves on the current Δ m s precision by a factor of two. We combine this result with previous LHCb measurements to determine Δ m s  = 17.7656 ± 0.0057 ps −1 , which is the legacy measurement of the original LHCb detector. The LHCb collaboration reports an improved measurement of the oscillation frequency of mesons consisting of a bottom quark and strange quark, which is then combined with previous results.

The Ξ b 0 → Ξ c + D s - and Ξ b - → Ξ c 0 D s - decays are observed for the first time using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of s = 13 TeV , corresponding to an integrated luminosity of 5.1 fb - 1 . The branching fractions times the production cross-sections of Ξ b baryons relative to that of Λ b 0 baryon are measured to be R Ξ b 0 Λ b 0 ≡ σ Ξ b 0 σ Λ b 0 × B Ξ b 0 → Ξ c + D s - B Λ b 0 → Λ c 0 D s - = ( 15.8 ± 1.1 ± 0.6 ± 7.7 ) % , R Ξ b - Λ b 0 ≡ σ Ξ b - σ Λ b 0 × B Ξ b - → Ξ c 0 D s - B Λ b 0 → Λ c 0 D s - = ( 16.9 ± 1.3 ± 0.9 ± 4.3 ) % , where the first uncertainties are statistical, the second systematic, and the third due to the uncertainties on the decay branching fractions of relevant charmed baryons. The masses of Ξ b 0 and Ξ b - baryons are measured to be m Ξ b 0 = 5791.12 ± 0.60 ± 0.45 ± 0.24 MeV / c 2 and m Ξ b - = 5797.02 ± 0.63 ± 0.49 ± 0.29 MeV / c 2 , where the uncertainties are statistical, systematic, and those due to charmed-hadron masses, respectively.

The polarimeter vector field for multibody decays of a spin-half baryon is intro duced as a generalisation of the baryon asymmetry parameters. Using a recent amplitude analysis of the Λ_(c)⁺ → pK⁻π⁺ decay performed at the LHCb experiment, we compute the distribution of the kinematic-dependent polarimeter vector for this process in the space of Mandelstam variables to express the polarised decay rate in a model-agnostic form. The obtained representation can facilitate polarisation measurements of the Λ_(c)⁺ baryon and eases inclusion of the Λ_(c)⁺ → pK⁻π⁺ decay mode in hadronic amplitude analyses.

The first measurement of J/ψ and D ⁰ production in PbNe collisions by the LHCb experiment in its fixed-target configuration is reported. The production of J/ψ and D ⁰ mesons is studied with a beam of lead ions with an energy of 2.5 TeV per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of √s̅_̅(̅\\̅s̅c̅r̅i̅p̅t̅s̅c̅r̅i̅p̅t̅s̅t̅y̅l̅e̅ ̅\\̅t̅e̅x̅t̅ ̅N̅N̅)̅ =68.5 \\text GeV. The J/ψ /D ⁰ production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from p\\text Ne collisions at the same energy and show no difference in the observed J/ψ suppression trend when comparing p\\text Ne and PbNe peripheral collisions with PbNe central collisions. Similar content being vie

The interpretation of cosmic antiproton flux measurements from space-borne experiments is currently limited by the knowledge of the antiproton production cross-section in collisions between primary cosmic rays and the interstellar medium. Using collisions of protons with an energy of 6.5$$\\,\\text {Te\\hspace{-1.00006pt}V}$$Te V incident on helium nuclei at rest in the proximity of the interaction region of the LHCb experiment, the ratio of antiprotons originating from antihyperon decays to prompt production is measured for antiproton momenta between 12 and$$110\\,\\text {Ge\\hspace{-1.00006pt}V\\!/}c $$110 Ge V\\!/ c . The dominant antihyperon contribution, namely$${\\overline{\\varLambda }} \\rightarrow {\\overline{{p}}} {{\\pi } ^+} $$Λ ¯ → p ¯ π + decays from promptly produced$$\\overline{\\varLambda }$$Λ ¯ particles, is also exclusively measured. The results complement the measurement of prompt antiproton production obtained from the same data sample. At the energy scale of this measurement, the antihyperon contributions to antiproton production are observed to be significantly larger than predictions of commonly used hadronic production models.

The measurement of charmonium states produced in proton-neon (pNe) collisions by the LHCb experiment in its fixed-target configuration is presented. The pro duction of J/ψ and ψ(2S) mesons is studied with a beam of 2.5 TeV protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy √s̅_̅(̅N̅N̅)̅ = 68.5 GeV. The data sample corresponds to an integrated luminosity of 21.7 ± 1.4 nb-1. The J/ψ and ψ(2S) hadrons are reconstructed in μ+μ- final states. The J/ψ production cross-section per target nucleon in the centre-of mass rapidity range y* ϵ [-2.29, 0] is found to be 506 ± 8 ± 46 nb/nucleon. The ratio of J/ψ and D0 cross-sections is evaluated to (1.06 ± 0.02 ± 0.09)%. The ψ(2S) to J/ψ relative production rate is found to be (1.67 ± 0.27 ± 0.10)% in good agreement with other measurements involving beam and target nuclei of similar sizes.

Using a proton–proton collision data sample collected by the LHCb detector and corresponding to an integrated luminosity of $5.7~\\text {fb}^{-1}$ , the lifetime of the light ${{B} ^0_{s}}$ mass eigenstate, $\\tau _{L}$ , is measured using the $B^0_s \\rightarrow J/\\psi \\eta$ decay mode to be $\\begin{aligned} \\tau _{\\text {L}} = 1.445 \\pm 0.016 \\text {(stat)} \\pm 0.008 \\text {(syst)} \\,\\text {ps}. \\end{aligned}$ A combination of this result with a previous LHCb analysis using an independent dataset corresponding to 3 fb–1 of integrated luminosity gives $\\begin{aligned} \\tau _{\\text {L}} = 1.452 \\pm 0.014 \\pm 0.007 \\pm 0.002 \\,\\text {ps}, \\end{aligned}$ where the first uncertainty is statistical, the second due to the uncorrelated part of the systematic uncertainty and the third due to the correlated part of the systematic uncertainty.

Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the D 0 D 0 π + mass spectrum just below the D *+ D 0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T c c + tetraquark with a quark content of c c u ¯ d ¯ and spin-parity quantum numbers J P  = 1 + . Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D *+ mesons is consistent with the observed D 0 π + mass distribution. To analyse the mass of the resonance and its coupling to the D * D system, a dedicated model is developed under the assumption of an isoscalar axial-vector T c c + state decaying to the D * D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T c c + state. In addition, an unexpected dependence of the production rate on track multiplicity is observed. The existence and properties of tetraquark states with two heavy quarks and two light antiquarks have been widely debated. Here, the authors use a unitarized model to study the properties of an exotic narrow state compatible with a doubly charmed tetraquark.

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. The Large Hadron Collider beauty collaboration reports a test of lepton flavour universality in decays of bottom mesons into strange mesons and a charged lepton pair, finding evidence of a violation of this principle postulated in the standard model.

A bstract An angular analysis of the rare decay B s 0 → ϕμ + μ − is presented, using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 8.4 fb − 1 . The observables describing the angular distributions of the decay B s 0 → ϕμ + μ − are determined in regions of q 2 , the square of the dimuon invariant mass. The results are consistent with Standard Model predictions.