Measurement of the cross-section ratio σ ( χ c 2 ) / σ ( χ c 1 ) for prompt χ c production at √ s = 7 TeV

Article history: Received 7 February 2012 Received in revised form 18 June 2012 Accepted 28 June 2012 Available online 4 July 2012 Editor: L. Rolandi The prompt production of the charmonium χc1 and χc2 mesons has been studied in proton–proton collisions at the Large Hadron Collider at a centre-of-mass energy of √ s = 7 TeV. The χc mesons are identified through their decays χc → J/ψγ with J/ψ → μ+μ− using 36 pb−1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two χc spin states, σ(χc2)/σ (χc1), has been determined as a function of the J/ψ transverse momentum, p J/ψ T , in the range from 2 to 15 GeV/c. The results are in agreement with the next-to-leading order non-relativistic QCD model at high p J/ψ T and lie consistently above the pure leading-order colour-singlet prediction. © 2012 CERN. Published by Elsevier B.V. Open access under CC BY-NC-ND license.