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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, pTJ/ψ, 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 pTJ/ψ and lie consistently above the pure leading-order colour-singlet prediction. © 2012 CERN.
Aaij, R., Abellan Beteta, C., Adeva, B., Adinolfi, M., Adrover, C., Affolder, A., … Zvyagin, A. (2012). Measurement of the cross-section ratio σ(χc2)/σ(χc1) for prompt χc production at s=7 TeV. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 714(2–5), 215–223. https://doi.org/10.1016/j.physletb.2012.06.077