Measurement of the (eta c)(1S) production cross-section in proton-proton collisions via the decay (eta c)(1S) -> p(p)over-bar

Abstract

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 centreof-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-hadron decays. The difference between the J/ψ and ηc(1S) meson masses is determined to be 114.7 ± 1.5 ± 0.1 MeV/c2 .