Abstract The B 0 → K ∗ 0 K ¯ ∗ 0 $$ {B}^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ and B s 0 → K ∗ 0 K ¯ ∗ 0 $$ {B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ decays are studied using ...proton-proton collision data corresponding to an integrated luminosity of 3 fb−1. An untagged and timeintegrated amplitude analysis of B (s) 0 → (K + π −)(K − π +) decays in two-body invariant mass regions of 150 MeV/c 2 around the K ∗0 mass is performed. A stronger longitudinal polarisation fraction in the B 0 → K ∗ 0 K ¯ ∗ 0 $$ {B}^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ decay, f L = 0.724 ± 0.051 (stat) ± 0.016 (syst), is observed as compared to f L = 0.240 ± 0.031 (stat) ± 0.025 (syst) in the B s 0 → K ∗ 0 K ¯ ∗ 0 $$ {B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ decay. The ratio of branching fractions of the two decays is measured and used to determine ℬ B 0 → K ∗ 0 K ¯ ∗ 0 = 8.0 ± 0.9 stat ± 0.4 syst × 10 − 7 $$ \mathrm{\mathcal{B}}\left({B}^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0}\right)=\left(8.0\pm 0.9\left(\mathrm{stat}\right)\pm 0.4\left(\mathrm{syst}\right)\right)\times {10}^{-7} $$ .
Abstract The prompt production of Λ c + baryons is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58 nb−1 ...recorded at a nucleon-nucleon centre-of-mass energy of s N N = 5.02 $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ TeV. Measurements of the differential cross-section and the forwardbackward production ratio are reported for Λ c + baryons with transverse momenta in the range 2 < p T < 10 GeV/c and rapidities in the ranges 1.5 < y ∗ < 4.0 and −4.5 < y ∗ < −2.5 in the nucleon-nucleon centre-of-mass system. The ratio of cross-sections of Λ c + baryons and D 0 mesons is also reported. The results are compared with next-to-leading order calculations that use nuclear parton distribution functions.
Abstract The production of ϒ(nS) mesons (n = 1, 2, 3) in pPb and Pbp collisions at a centre-of-mass energy per nucleon pair s N N = 8.16 $$ \sqrt{s_{\mathrm{NN}}}=8.16 $$ TeV is measured by the LHCb ...experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb−1. The ϒ(nS) mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the ϒ(1S) and ϒ(2S) states, their forward-to-backward ratios and nuclear modification factors. The measurements are performed as a function of the transverse momentum p T and rapidity in the nucleon-nucleon centre-of-mass frame y * of the ϒ(nS) states, in the kinematic range p T < 25 GeV/c and 1.5 < y * < 4.0 (−5.0 < y * < −2.5) for pPb (Pbp) collisions. In addition, production cross-sections for ϒ(3S) are measured integrated over phase space and the production ratios between all three ϒ(nS) states are determined. Suppression for bottomonium in proton-lead collisions is observed, which is particularly visible in the ratios. The results are compared to theoretical models.
Abstract Measurements are reported of the central exclusive production of J/ψ and ψ(2S) mesons in pp collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to ...previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2.0 < η < 4.5, are measured to be σ J / ψ → μ + μ − = 435 ± 18 ± 11 ± 17 p b σ ψ 2 S → μ + μ − = 11.1 ± 1.1 ± 0.3 ± 0.4 p b . $$ \begin{array}{c}\hfill {\sigma}_{J/\psi \to {\mu}^{+}{\mu}^{-}} = 435 \pm 18 \pm 11 \pm 17\ \mathrm{p}\mathrm{b}\hfill \\ {}\hfill {\sigma}_{\psi (2S)\to {\mu}^{+}{\mu}^{-}} = 11.1 \pm 1.1 \pm 0.3 \pm 0.4\ \mathrm{p}\mathrm{b}.\hfill \end{array} $$ The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.
Abstract The inclusive D s ± production asymmetry is measured in pp collisions collected by the LHCb experiment at centre-of-mass energies of s=7 $$ \sqrt{s}=7 $$ and 8 TeV. Promptly produced D s ± ...mesons are used, which decay as D s ± → ϕπ±, with ϕ → K + K −. The measurement is performed in bins of transverse momentum, p T, and rapidity, y, covering the range 2.5 < p T < 25.0 GeV/c and 2.0 < y < 4.5. No kinematic dependence is observed. Evidence of nonzero D s ± production asymmetry is found with a significance of 3.3 standard deviations.
Abstract Forward top quark pair production is studied in pp collisions in the μeb final state using a data sample corresponding to an integrated luminosity of 1.93 fb−1 collected with the LHCb ...experiment at a centre-of-mass energy of 13 TeV. The cross-section is measured in a fiducial region where both leptons have a transverse momentum greater than 20 GeV and a pseudorapidity between 2.0 and 4.5. The quadrature sum of the azimuthal separation and the difference in pseudorapidities, denoted ΔR, between the two leptons must be larger than 0.1. The b-jet axis is required to be separated from both leptons by a ΔR of 0.5, and to have a transverse momentum in excess of 20 GeV and a pseudorapidity between 2.2 and 4.2. The cross-section is measured to be σtt¯=126±19stat±16syst±5lumifb $$ {\sigma}_{t\overline{t}}=126\pm 19\left(\mathrm{stat}\right)\pm 16\left(\mathrm{syst}\right)\pm 5\left(\mathrm{lumi}\right)\mathrm{f}\mathrm{b} $$ where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measurement is compatible with the Standard Model prediction.
Abstract A measurement of Z → τ + τ − production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb−1, from pp collisions at s=8 $$ \sqrt{s}=8 $$ TeV collected ...by the LHCb experiment. The τ + τ − candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for Z bosons with invariant mass between 60 and 120 GeV/c 2, which decay to tau leptons with transverse momenta greater than 20 GeV/c and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be σpp→Z→τ+τ−=95.8±2.1±4.6±0.2±1.1 $$ {\sigma}_{pp}{{}_{\to Z\to {\tau}^{+}}}_{\tau^{-}}=95.8 \pm 2.1 \pm 4.6 \pm 0.2 \pm 1.1 $$ pb, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for Z → τ + τ − to Z → μ + μ − (Z → e + e −), determined to be 1.01 ± 0.05 (1.02 ± 0.06), is consistent with the lepton-universality hypothesis in Z decays.
Abstract A search for the decay BS0→K¯∗0μ+μ− $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ is presented using data sets corresponding to 1.0, 2.0 and 1.6 fb−1 of integrated luminosity ...collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the BS0→K¯∗0μ+μ− $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ decay is determined to be ℬBs0→K¯∗0μ+μ−=2.9±1.0stat±0.2syst±0.3norm×10−8 $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-}\right)=\left2.9\pm 1.0\left(\mathrm{stat}\right)\pm 0.2\left(\mathrm{syst}\right)\pm 0.3\left(\mathrm{norm}\right)\right\times {10}^{-8} $$, where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement.
Abstract The production cross-sections of ϒ(1S), ϒ(2S) and ϒ(3S) mesons in proton-proton collisions at s = 13 $$ \sqrt{s}=13 $$ TeV are measured with a data sample corresponding to an integrated ...luminosity of 277 ± 11 pb−1 recorded by the LHCb experiment in 2015. The ϒ mesons are reconstructed in the decay mode ϒ → μ + μ −. The differential production cross-sections times the dimuon branching fractions are measured as a function of the ϒ transverse momentum, p T, and rapidity, y, over the range 0 < p T < 30 GeV/c and 2.0 < y < 4.5. The ratios of the cross-sections with respect to the LHCb measurement at s = 8 $$ \sqrt{s}=8 $$ TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.
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