Abstract
Using a data sample corresponding to an integrated luminosity of 2.0 , text {fb} ^{-1}, collected by the LHCb experiment, the production of the {eta _{c}} (1S) state in proton–proton collisions at a centre-of-mass energy of sqrt{s} =13, text {TeV} is studied in the rapidity range 2.0< y < 4.5 and in the transverse momentum range 6.5< p_{mathrm {T}} < 14.0 , text {GeV} . The cross-section for prompt production of {eta _{c}} (1S) mesons relative to that of the {J /psi } meson is measured using the p overline{{p}} decay mode and is found to be {sigma _{{eta _{c}} (1S)}/sigma _{{{J /psi }}} = 1.69 pm 0.15 pm 0.10 pm 0.18}. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the {{J /psi }} !rightarrow {p} {overline{{p}}} and {eta _{c}} !rightarrow {p} {overline{{p}}} decays. The prompt {eta _{c}} (1S) production cross-section is determined to be {sigma _{{eta _{c}} (1S)} = 1.26 pm 0.11pm 0.08pm 0.14 ,upmu text {b}}, where the last uncertainty includes that on the {J /psi } meson cross-section. The ratio of the branching fractions of b -hadron decays to the {eta _{c}} (1S) and {J /psi } states is measured to be {{mathcal {B}} _{{b} !rightarrow {eta _{c}} X}/{mathcal {B}} _{{b} !rightarrow {{J /psi }} X} = 0.48 pm 0.03 pm 0.03 pm 0.05}, where the last uncertainty is due to those on the branching fractions of the {{J /psi }} !rightarrow {p} {overline{{p}}} and {eta _{c}} !rightarrow {p} {overline{{p}}} decays. The difference between the {J /psi } and {eta _{c}} (1S) masses is also determined to be 113.0 pm 0.7 pm 0.1 , text {MeV} , which is the most precise single measurement of this quantity to date.
Highlights
Nonrelativistic quantum chromodynamics (NRQCD) [1] is a powerful framework to describe the production from initial parton scattering of charmonium states with quantum numbers J PC = 1−−, for instance the J/ψ meson, over a wide range of transverse momentum, pT, and rapidity, y
It remains a challenge to provide a comprehensive theoretical description of measurements of the prompt production, comprising the hadroproduction and feed-down from excited resonant states, and the polarisation of J/ψ mesons at the Tevatron [2] and the LHC [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] collision energies over the entire pT range
A factorisation approach together with a heavy-quark spin symmetry assumption allows the simultaneous treatment of J/ψ and ηc(1S)1 production observables by imposing relations between their long-distance matrix elements (LDME) [1]
Summary
It remains a challenge to provide a comprehensive theoretical description of measurements of the prompt production, comprising the hadroproduction and feed-down from excited resonant states, and the polarisation of J/ψ mesons at the Tevatron [2] and the LHC [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17] collision energies over the entire pT range. A simultaneous study of the hadroproduction and production in inclusive b-hadron decays of the charmonium states with linked LDMEs provides a unique test of basic NRQCD assumptions [34]. Both J/ψ and ηc mesons are reconstructed via their decays to p p
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