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.