Measurement of the η[subscript c](1S) production cross-section in proton–proton collisions via the decay η[subscript c](1S) → p[bar over p]

Abstract

The production of the η[subscript c](1S) state in proton-proton collisions is probed via its decay to the p[bar over p] final state with the LHCb detector, in the rapidity range 2.0 < y < 4.5 and in the meson transverse-momentum range p[subscript T] > 6.5 GeV/c. The cross-section for prompt production of η[subscript c](1S) mesons relative to the prompt J/ψ cross-section is measured, for the first time, to be [superscript σ]η[subscript c](1S)/σ[subscript J/ψ] = 1.74 ± 0.29 ± 0.28 ± 0.18[subscript B] at a centre-of-mass energy √s = 7 TeV using data corresponding to an integrated luminosity of 0.7 fb[superscript −1], and [superscript σ]η[subscript c](1S)/σ[subscript J/ψ] = 1.60 ± 0.29 ± 0.25 ± 0.17[subscript B] at √s = 8 TeV using 2.0 fb[superscript −1]. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the η[subscript c](1S) and J/ψ decays to the p[bar over p] final state. In addition, the inclusive branching fraction of b-hadron decays into η[subscript c](1S) mesons is measured, for the first time, to be B(b → η[subscript c]X) = (4.88 ± 0.64 ± 0.29 ± 0.67[subscript B]) × 10[superscript −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[subscript c](1S) meson masses is determined to be 114.7 ± 1.5 ± 0.1 MeV/c[superscript 2].