Measurement of J/Ψ production in pp collisions at s√=7 TeV

The production of J/ψ mesons in proton-proton collisions at s√=7\tev is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/ψ production is measured as a function of the J/ψ transverse momentum p_{\rm T}\ and rapidity y in the fiducial region pT∈[0;14]\gevc and y∈[2.0;4.5]. The differential cross-section and fraction of \j psi\ from b-hadron decays are also measured in the same p_{\rm T}\ and y range s. The analysis is based on a data sample corresponding to an integrated luminos ity of 5.2\pbinv. The measured cross-sections integrated over the fiducial region are 10.52±0.04±1.40+1.64−2.20\microb for prompt J/ψ production and 1.14±0.01±0.16\microb for J/ψ from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/ψ production cross-section is obtained assuming no J/ψ polarisation and the third error indicates the acceptance uncertainty due to this assumption.