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

TL;DR

This study measures inclusive psi(2S) production in p-Pb collisions at the LHC, revealing a stronger suppression of psi(2S) compared to J/psi, especially at backward rapidity, suggesting significant final state effects.

Contribution

First measurement of inclusive psi(2S) production in p-Pb collisions at the LHC, highlighting unexpected suppression patterns not explained by existing models.

Findings

psi(2S) is suppressed relative to pp collisions

Suppression is stronger at backward rapidity

Final state effects influence psi(2S) production

Abstract

The ALICE Collaboration has studied the inclusive $\psi(\rm 2S)$ production in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV at the CERN LHC. Measurements are performed, in the $\mu^{+}\mu^{-}$ decay channel, in a forward (2.03$<y_{\rm cms}<$3.53) and in a backward (-4.46$<y_{\rm cms}<$-2.96) centre of mass rapidity ranges, as a function of transverse momentum or event activity. The $\psi(\rm 2S)$ production is compared to the $\rm J/\psi$ 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 $\psi(\rm 2S)$ production is suppressed with respect to pp and, in particular in the backward rapidity region, the suppression is stronger than the $\rm J/\psi$ one. This unexpected difference between the $\rm J/\psi$ and $\psi(\rm 2S)$ 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 $\psi(\rm 2S)$ production.