Inclusive ψ(2S) production in p–Pb collisions with ALICE

Abstract The ALICE Collaboration has studied the inclusive ψ ( 2 S ) production in p–Pb collisions at s NN = 5.02 TeV at the CERN LHC. Measurements are performed, in the μ + μ − decay channel, in a forward ( 2.03 y cms 3.53 ) and in a backward ( − 4.46 y cms − 2.96 ) centre of mass rapidity ranges, as a function of transverse momentum or event activity. The ψ ( 2 S ) production is compared to the J / ψ one through the double ratio [ σ ψ ( 2 S ) / σ J / ψ ] pPb / [ σ ψ ( 2 S ) / σ J / ψ ] pp between the cross sections evaluated in p–Pb and pp collisions and by calculating the J / ψ and ψ ( 2 S ) nuclear modification factors. Results indicate that the ψ ( 2 S ) production is suppressed with respect to pp and, in particular in the backward rapidity region, the suppression is stronger than the J / ψ one. This unexpected difference between the J / ψ and ψ ( 2 S ) behaviour, not accounted for by theoretical models based on nuclear parton shadowing and coherent energy loss mechanisms, indicates the presence of sizeable final state effects on the ψ ( 2 S ) production.