Suppression of psi(2S) production in p-Pb collisions at root sNN = 5.02 TeV

The ALICE Collaboration has studied the inclusive production of the charmonium state psi(2S) in proton-lead (p-Pb) collisions at the nucleon-nucleon centre of mass energy root sNN=5.02TeV at the CERN LHC. The measurement was performed at forward(2.03 < y<INF>cms</INF> < 3.53) and backward (-4.46 < y<INF>cms</INF> < -2.96) centre of mass rapidities, studying the decays into muon pairs. In this paper, we present the inclusive production cross sections sigma<INF>psi(2S)</INF>, both integrated and as a function of the transverse momentum pT, for the two y<INF>cms</INF> domains. The results are compared to those obtained for the 1S vector state (J/psi), by showing the ratios between the production cross sections, as well as the double ratios [sigma<INF>psi(2S)</INF>/sigma<INF>J/psi</INF>]pPb/[sigma<INF>&<INF>(2S)</INF>/sigma J/&PSI]pp between p-Pb and proton-proton collisions. Finally, the nuclear modification factor for inclusive psi(2S) is evaluated and compared to the measurement of the same quantity for J/psi and to theoretical models including parton shadowing and coherent energy loss mechanisms. The results show a significantly larger suppression of the psi(2S) compared to that measured for J/psi and to models. These observations represent a clear indication for sizeable final state effects on psi(2S) production.