Inclusive Psi(2S) production in p-Pb collisions with ALICE

The ALICE Collaboration has studied the inclusive $\psi (2\mathrm{S})$ production in p-Pb collisions at $\sqrt{s_{\mathrm{N}\mathrm{N}}}=5.02$ TeV at the CERN LHC. Measurements are performed, in the ${\mu }^{+}{\mu }^{-}$ decay channel, in a forward (2.03$<y_{\mathrm{c}\mathrm{m}\mathrm{s}}<$3.53) and in a backward (-4.46$<y_{\mathrm{c}\mathrm{m}\mathrm{s}}<$-2.96) centre of mass rapidity ranges, as a function of transverse momentum or event activity. The $\psi (2\mathrm{S})$ production is compared to the $\mathrm{J}\mathrm{/}\psi$ one through the double ratio $[\sigma_{\psi(\rm 2S)}/\sigma_{\rm J/\psi}]{\rm pPb}/[\sigma{\psi(\rm 2S)}/\sigma_{\rm J/\psi}]_{\rm pp}$ between the cross sections evaluated in p-Pb and pp collisions and by calculating the $\rm J/\psi$and$\psi(\rm 2S)$ nuclear modification factors. Results indicate that the $\psi (2\mathrm{S})$ production is suppressed with respect to pp and, in particular in the backward rapidity region, the suppression is stronger than the $\mathrm{J}\mathrm{/}\psi$ one. This unexpected difference between the $\mathrm{J}\mathrm{/}\psi$ and $\psi (2\mathrm{S})$ 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 $\psi (2\mathrm{S})$ production.