Measurement of the ratio of prompt χc to J/ψ production in pp collisions at s=7 TeV

The prompt production of charmonium χc and J/ψ states is studied in proton-proton collisions at a centre-of-mass energy of s=7 TeV at the Large Hadron Collider. The χc and J/ψ mesons are identified through their decays χc→J/ψγ and 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 χc and J/ψ, σ(χc→J/ψγ)/σ(J/ψ), is determined as a function of the J/ψ transverse momentum in the range 2