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

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5.02 TeV
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The ALICE Collaboration has studied the inclusive production of the charmonium state $\psi(\rm 2S)$ in proton-lead (\mbox{p-Pb}) collisions
at the nucleon-nucleon centre of mass energy $\sqrt{s_{\rm NN}}$ = 5.02 TeV at the CERN LHC.
The measurement was performed at forward ($2.03<y_{\rm cms}<3.53$) and backward ($-4.46<y_{\rm cms}<-2.96$) centre of mass rapidities, studying the decays into muon pairs. In this paper, we present the inclusive production cross sections $\sigma_{\psi(\rm 2S)}$, both integrated and as a function of the transverse momentum $p_{\rm T}$, for the two $y_{\rm cms}$ domains.
The results are compared to those obtained for the 1S vector state (J/$\psi$), by showing the ratios between the cross sections,
as well as the double ratios $[\sigma_{\psi(\rm 2S)}/\sigma_{\rm J/\psi}]_{\rm pPb}/[\sigma_{\psi(\rm 2S)}/\sigma_{\rm J/\psi}]_{\rm pp}$ between \mbox{p-Pb} and proton-proton collisions.
Finally, the nuclear modification factor for inclusive $\psi(\rm 2S)$ was 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 $\psi(\rm 2S)$ relative to that measured for J/$\psi$ and to models.
These observations represent a clear indication for sizeable final state effects on $\psi(\rm 2S)$.