Centrality dependence of $\mathbfψ$(2S) suppression in p-Pb collisions at $\mathbf{\sqrt{{\textit s}_{\rm NN}}}$ = 5.02 TeV

Abstract

The inclusive production of the $ψ$(2S) charmonium state was studied as a function of centrality in p-Pb collisions at the nucleon-nucleon center of mass energy $\sqrt{s_{\rm NN}}$ = 5.02 TeV at the CERN LHC. The measurement was performed with the ALICE detector in the center of mass rapidity ranges $-4.46<y_{\rm cms}<-2.96$ and $2.03<y_{\rm cms}<3.53$, down to zero transverse momentum, by reconstructing the $ψ$(2S) decay to a muon pair. The $ψ$(2S) production cross section $σ_{ψ(\rm 2S)}$ is presented as a function of the collision centrality, which is estimated through the energy deposited in forward rapidity calorimeters. The relative strength of nuclear effects on the $ψ$(2S) and on the corresponding 1S charmonium state J/$ψ$ is then studied by means of the double ratio of cross sections $[σ_{ψ(\rm 2S)}/σ_{\rm J/ψ}]_{\rm pPb}/[σ_{ψ(\rm 2S)}/σ_{\rm J/ψ}]_{\rm pp}$ between p-Pb and pp collisions, and by the values of the nuclear modification factors for the two charmonium states. The results show a large suppression of $ψ$(2S) production relative to the J/$ψ$ at backward (negative) rapidity, corresponding to the flight direction of the Pb-nucleus, while at forward (positive) rapidity the suppressions of the two states are comparable. Finally, comparisons to results from lower energy experiments and to available theoretical models are presented.