Measurement of ψ (2S) meson production in pp collisions at √s =7 TeV

The differential cross-section for the inclusive production of ψ(2S) mesons in pp collisions at √s = 7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated luminosity of 36 pb^-1. The ψ(2S) mesons are reconstructed in the decay channels ψ(2S)→μ⁺μ^- and ψ(2S)→J/ψπ⁺π^-, with the J/ψ meson decaying into two muons. Results are presented both for promptly produced ψ(2S) mesons and for those originating from b-hadron decays. In the kinematic range p_T(ψ(2S))≤16 GeV/c and 2<y(ψ(2S))≤4. 5 we measure σ_prompt(ψ(2S)) = 1.44±0.01 (stat)±0.12 (syst)_-0.40^0.20 (pol) μb, σ_b(ψ(2S))= 0.25±0.01 (stat)±0.02 (syst) μb, where the last uncertainty on the prompt cross-section is due to the unknown ψ(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/ψ measurements we determine the inclusive branching fraction B(b→ψ(2S)X) =(2.73±0.06 (stat)±0.16(syst)±0.24(BF))×10^-3, where the last uncertainty is due to the B(b→J/ψX), B(J/ψ→μ⁺μ^-) and B(ψ(2S)→e⁺e^-) branching fraction uncertainties.