Shadowing effects onJ/ψandΥproduction at energies available at the CERN Large Hadron Collider

Abstract

Background: Proton-nucleus collisions have been used as a intermediate baseline for the determination of cold medium effects. They lie between proton-proton collisions in vacuum and nucleusnucleus collisions which are expected to be dominated by hot matter effects. Modifications of the quark densities in nuclei relative to those of the proton are well established although those of the gluons in the nucleus are not well understood. The effect of these modifications on quarkonium production are studied in proton-lead collisions at the LHC at a center of mass energy of 5.02 TeV. Purpose: The possibility of whether the LHC proton-lead data can be described by nuclear modifications of the parton densities, referred to as shadowing, alone is examined. The results are compard to the nuclear modification factor and to the forward-backward ratio, both as a function of transverse momentum, pT , and rapidity, y. Methods: The color evaporation model of quarkonium production is employed at next-to-leading order in the total cross section and leading order in the transverse momentum dependence. The EPS09 NLO modifications are used as a standard of comparison. The effect of the proton parton density and the choice of shadowing parameterization on the pT and rapidity dependence of the result is studied. The consistency of the shadowing calculations at leading and next-to-leading order are checked. The size of the mass and scale uncertainties relative to the uncertainty on the shadowing parameterization is also investigated. Finally, whether the expected cold matter effect in nucleus-nucleus collisions can be modeled as the product of proton-nucleus results at forward and backward rapidity is studied. Results: The rapidity and pT dependence of the nuclear modification factor is found to be generally consistent with the next-to-leading order calculations in the color evaporation model. The forwardbackward ratio is more difficult to describe with shadowing alone. The leading and next-to-leading order calculations are inconsistent for EPS09 while other available parameterizations are consistent. The mass and scale uncertainties on quarkonium production are larger than those of the nuclear parton densities. Conclusions: While shadowing is consistent with the nuclear suppression factors within the uncertainties, it is not consistent with the measured forward-backward asymmetry, especially as a function of transverse momentum. Data from p + p collisions at the same energy are needed.

Centrality dependence of ψ(2S) suppression in p-Pb collisions at s N N = 5.02 $$ {\sqrt{s}}_{\mathrm{NN}}=5.02 $$ TeV

“…In the most central collisions, the difference between the measured Q pPb corresponds to 4.3σ, while, integrating over centrality, suppressions differ by 4.1σ. The results are compared to calculations including either only shadowing (EPS09 LO [11], EPS09 NLO [44]) or only coherent energy loss [45] and to models implementing final state interactions (co-movers [11], QGP+HRG [26]). While the J/ψ results are reproduced by shadowing/energy loss calculations, additional final state effects, as those discussed in the context of figure 3, are needed to describe the ψ(2S) results, in particular at backward rapidity.…”

“…We use the J/ψ p T as a proxy for the average p T of the cc pair, as the Figure 4. J/ψ [27] and ψ(2S) nuclear modification factors, Q pPb , shown as a function of N coll for the backward (left) and forward (right) rapidity regions and compared to theoretical models [11,26,44,45]. The boxes around unity correspond to the global ψ(2S) systematic uncertainties at forward (red box) and backward (blue box) rapidities.…”

“…The value m cc = 3.4 GeV/c 2 was chosen for the (average) mass of the evolving cc pair [9,47], while m T,cc was calculated in each centrality bin starting from the measured J/ψ p T values [27]. We use the J/ψ p T as a proxy for the average p T of the cc pair, as the [11,26,44,45]. The boxes around unity correspond to the global ψ(2S) systematic uncertainties at forward (red box) and backward (blue box) rapidities.…”

bb¯ kinematic correlations in cold nuclear matter

“…However, EPPS16 has five additional parameters relative to EPS09, resulting in larger uncertainty bands with an uncertainty of 25-30% due to shadowing [37]. Although the uncertainty due to shadowing is significant, it is smaller than the uncertainties due to the heavy quark mass and scale variations, particularly for charm quarks [38]. The larger bottom quark mass and comparably larger scales reduces both the overall uncertainty in the baseline p + p cross section and the shadowing effect in p+Pb and Pb+Pb collisions because of the larger parton momentum fraction accessed and the evolution of the shadowing due to the larger factorization scale.…”

In-medium charmonium production in proton-nucleus collisions

“…4, our J/ψ and ψ(2S) calculations are compared to 5.02 TeV ALICE data. The black bands show only the CNM effects, bounded by the anti-/shadowing obtained from EPS09-LO and EPS09-NLO calculations [47,48] for both charmonia and open charm; as for the RHIC case, the centrality dependence of shadowing is mimicked by a nuclear absorptiontype behavior, while for anti-shadowing we employ a parameterization of the pertinent lines shown in Fig. 3 of Ref.…”