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

Abstract

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