Centrality dependence of J/ψ and ψ(2S) production and nuclear modification in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV

Abstract

The inclusive production of the J/ψ and ψ(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 8.16 TeV at the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals −4.46 < ycms< −2.96 (Pb-going direction) and 2.03 < ycms< 3.53 (p-going direction), down to zero transverse momentum (pT). The J/ψ and ψ(2S) production cross sections are evaluated as a function of the collision centrality, estimated through the energy deposited in the zero degree calorimeter located in the Pb-going direction. The pT-differential J/ψ production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average 〈pT〉 and $$ \left\langle {p}_{\mathrm{T}}^2\right\rangle $$ p T 2 values. The nuclear effects affecting the production of both charmonium states are studied using the nuclear modification factor. In the p-going direction, a suppression of the production of both charmonium states is observed, which seems to increase from peripheral to central collisions. In the Pb-going direction, however, the centrality dependence is different for the two states: the nuclear modification factor of the J/ψ increases from below unity in peripheral collisions to above unity in central collisions, while for the ψ(2S) it stays below or consistent with unity for all centralities with no significant centrality dependence. The results are compared with measurements in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV and no significant dependence on the energy of the collision is observed. Finally, the results are compared with theoretical models implementing various nuclear matter effects.

Measurement of $ψ(2S)$ nuclear modification at backward and forward rapidity in $p$$+$$p$, $p$$+$Al, and $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

“…Additionally, to isolate modification due to final-state effects, measuring the ψ(2S) to J/ψ ratio mostly removes initial-state effects. The PHENIX ψ(2S) measurements are presented alongside corresponding measurements from the ALICE and LHCb Collaborations [9,10,20,24,25]. Figure 3 shows the J/ψ and ψ(2S) nuclear modification factors as a function of rapidity in p+Al collisions.…”

“…Figures 5 and 6 show the J/ψ [24] and ψ(2S) nuclear modification measurements as a function of N coll . The nuclear modification between the two states follows a similar trend at forward rapidity, with the ψ(2S) modification showing slightly stronger suppression.…”

“…Figure 7 shows the PHENIX ψ(2S) and the ALICE ψ(2S) nuclear-modification factors [24] as a function of N coll . Due to the higher energy at the LHC, the nucleon-nucleon cross section is larger, which leads to a larger range of N coll values for the ALICE data.…”

“…Figure 8 compares the ψ(2S) to J/ψ ratios for PHENIX and ALICE [24] as a function of N coll . The PHENIX ψ(2S) to J/ψ ratio in p+p collisions is shown at N coll = 1.…”

“…The ATLAS collaboration has reported J/ψ [21] and charmonium [22] measurements. The J/ψ [19,20] and ψ(2S) [9,23] nuclear modification has been published by the ALICE collaboration, and more recently [24] at √ s N N = 8. 16 TeV.…”