Measurement of the ηc(1S) production cross-section in proton-proton collisions via the decay ηc(1S) → pp



    CERN-LHC. The production of the ηc(1S) state in proton-proton collisions is probed via its decay to the pp final state with the LHCb detector, in the rapidity range 2.0<y<4.5 and in the meson transverse-momentum range pT>6.5 GeV/c. The cross-section for prompt production of ηc(1S) mesons relative to the prompt J/ψ cross-section is measured, for the first time, to be

    σηc(1S)/σJ/ψ = 1.74±0.29±0.28±0.18B

    at a centre-of-mass energy √s=7 TeV using data corresponding to an integrated luminosity of 0.7 fb−1, and

    σηc(1S)/σJ/ψ = 1.60±0.29±0.25±0.17B

    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 ηc(1S)
    and J/ψ decays to the pp final state. In addition, the inclusive branching fraction of b-hadron decays into ηc(1S) mesons is measured, for the first time, to be

    B(b→ηcX)=(4.88±0.64±0.29±0.67B) × 10−3,

    where the third uncertainty includes also the uncertainty on the J/ψ
    inclusive branching fraction from b
    b-hadron decays. The difference between the J/ψ and ηc(1S) meson masses is determined to be 114.7±1.5±0.1MeV/c2.
    Date made available4 Jan 2015

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