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The production of the η c ( 1 S ) state in proton-proton collisions is probed via its decay to the p p ¯ final state with the LHCb detector, in the rapidity range 2.0 < y < 4.5 and in the meson transverse-momentum range p T > 6.5 GeV / c . The cross-section for prompt production of η c ( 1 S ) mesons relative to the prompt J / ψ cross-section is measured, for the first time, to be σ η c ( 1 S ) / σ J / ψ = 1.74 ± 0.29 ± 0.28 ± 0 . 18 B at a centre-of-mass energy s = 7 TeV using data corresponding to an integrated luminosity of 0.7 fb - 1 , and σ η c ( 1 S ) / σ J / ψ = 1.60 ± 0.29 ± 0.25 ± 0 . 17 B at s = 8 TeV using 2.0 fb - 1 . The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the η c ( 1 S ) and J / ψ decays to the p p ¯ final state. In addition, the inclusive branching fraction of b -hadron decays into η c ( 1 S ) mesons is measured, for the first time, to be B ( b → η c X ) = ( 4.88 ± 0.64 ± 0.29 ± 0 . 67 B ) × 10 - 3 , where the third uncertainty includes also the uncertainty on the J / ψ inclusive branching fraction from b -hadron decays. The difference between the J / ψ and η c ( 1 S ) meson masses is determined to be 114.7 ± 1.5 ± 0.1 MeV / c 2 .

A bstract The differential branching fraction of the rare decay Λ b 0  →  Λμ + μ − is measured as a function of q 2 , the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of 3 . 0 fb −1 , collected by the LHCb experiment. Evidence of signal is observed in the q 2 region below the square of the J/ψ mass. Integrating over 15 < q 2 < 20 GeV 2 /c 4 the differential branching fraction is measured as d ℬ Λ b 0 → Λ μ + μ − / d q 2 = 1.18 − 0.08 + 0.09 ± 0.03 ± 0.27 × 10 − 7 GeV 2 / c 4 − 1 , where the uncertainties are statistical, systematic and due to the normalisation mode, Λ b 0  →  J / ψΛ , respectively. In the q 2 intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon ( A FB ℓ ) and hadron ( A FB h ) systems are measured for the first time. In the range 15 < q 2 < 20 GeV 2 /c 4 they are found to be A F B ℓ = − 0.05 ± 0.09 stat ± 0.03 syst and A F B h = − 0.29 ± 0.07 stat ± 0.03 syst .

A bstract A study is presented of central exclusive production of Υ( nS ) states, where the Υ( nS ) resonances decay to the μ + μ − final state, using pp collision data recorded by the LHCb experiment. The cross-section is measured in the rapidity range 2 < y (Υ) < 4 . 5 where the muons are reconstructed in the pseudorapidity range 2 < η ( μ ± ) < 4 . 5. The data sample corresponds to an integrated luminosity of 2.9 fb −1 and was collected at centre-of-mass energies of 7 TeV and 8 TeV. The measured Υ(1 S ) and Υ(2 S ) production cross-sections are σ pp → p Υ 1 S p = 9.0 ± 2.1 ± 1.7 p b and σ pp → p Υ 2 S p = 1.3 ± 0.8 ± 0.3 p b , where the first uncertainties are statistical and the second are systematic. The Υ(1 S ) crosssection is also measured as a function of rapidity and is found to be in good agreement with Standard Model predictions. An upper limit is set at 3.4 pb at the 95% confidence level for the exclusive Υ(3 S ) production cross-section, including possible contamination from χ b (3 P ) → Υ(3 S )γ decays.

A bstract The production of J/ψ mesons in proton-proton collisions at a centre-of-mass energy of s = 13 TeV is studied with the LHCb detector. Cross-section measurements are performed as a function of the transverse momentum p T and the rapidity y of the J/ψ meson in the region p T < 14 GeV/ c and 2 . 0 < y < 4 . 5, for both prompt J/ψ mesons and J/ψ mesons from b -hadron decays. The production cross-sections integrated over the kinematic coverage are 15 . 30 ± 0 . 03 ± 0 . 86 μb for prompt J/ψ and 2 . 34 ± 0 . 01 ± 0 . 13 μb for J/ψ from b -hadron decays, assuming zero polarization of the J/ ψ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for J/ψ mesons from b -hadron decays is used to extrapolate to a total b b ¯ cross-section. The ratios of the cross-sections with respect to s = 8 TeV are also determined.

A bstract A measurement of the production cross-section for Z bosons that decay to muons is presented. The data were recorded by the LHCb detector during pp collisions at a centre-of-mass energy of 7 TeV, and correspond to an integrated luminosity of 1.0 fb −1 . The cross-section is measured for muons in the pseudorapidity range 2 . 0 < η < 4 . 5 with transverse momenta p T > 20 GeV /c . The dimuon mass is restricted to 60 < M μ + μ − < 120 GeV /c 2 . The measured cross-section is σ Z → μ + μ − = 76.0 ± 0.3 ± 0.5 ± 1.0 ± 1.3 p b where the uncertainties are due to the sample size, systematic effects, the beam energy and the luminosity. This result is in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. The cross-section is also measured differentially as a function of kinematic variables of the Z boson. Ratios of the production cross-sections of electroweak bosons are presented using updated LHCb measurements of W boson production. A precise test of the Standard Model is provided by the measurement of the ratio σ W + → μ + ν μ + σ W − → μ − ν ¯ μ σ Z → μ + μ − = 20.63 ± 0.09 ± 0.12 ± 0.05 , where the uncertainty due to luminosity cancels.

A search for the doubly charmed baryon Xi_cc^+ in the decay mode Xi_cc^+ -> Lambda_c^+ K^- pi^+ is performed with a data sample, corresponding to an integrated luminosity of 0.65/fb, of pp collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV/c^2. Upper limits at the 95% confidence level on the ratio of the Xi_cc^+ production cross-section times branching fraction to that of the Lambda_c^+, R, are given as a function of the Xi_cc^+ mass and lifetime. The largest upper limits range from R < 1.4 x 10^-2 for a lifetime of 100 fs to R < 3.4 x 10^-4 for a lifetime of 400 fs.