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Impact of the Nuclear Modification of the Gluon Densities on J/Psi production in pPb collisions at sqrt(s_NN) = 5 TeV

E. G. Ferreiro, F. Fleuret, J. P. Lansberg, A. Rakotozafindrabe

Abstract

We update our previous studies of nuclear-matter effects on J/Psi production in proton-nucleus for the recent LHC pPb runs at sqrt(s_NN)=5 TeV. We have analysed the effects of the modification of the gluon PDFs in nucleus, using an exact kinematics for a 2->2 process, namely g+g->J/Psi+g as expected from LO pQCD. This allows to constrain the transverse-momentum while computing the nuclear modification factor for different rapidities, unlike with the usual simplified kinematics. Owing to the absence of measurement in pp collisions at the same sqrt(s_NN) and owing to the expected significant uncertainties in yield interpolations which would hinder definite interpretations of nuclear modification factor --R_pPb--, we have derived forward-to-backward and central-to-peripheral yield ratios in which the unknown proton-proton yield cancel. These have been computed without and with a transverse-momentum cut, e.g. to comply with the ATLAS and CMS constraints in the central-rapidity region.

Impact of the Nuclear Modification of the Gluon Densities on J/Psi production in pPb collisions at sqrt(s_NN) = 5 TeV

Abstract

We update our previous studies of nuclear-matter effects on J/Psi production in proton-nucleus for the recent LHC pPb runs at sqrt(s_NN)=5 TeV. We have analysed the effects of the modification of the gluon PDFs in nucleus, using an exact kinematics for a 2->2 process, namely g+g->J/Psi+g as expected from LO pQCD. This allows to constrain the transverse-momentum while computing the nuclear modification factor for different rapidities, unlike with the usual simplified kinematics. Owing to the absence of measurement in pp collisions at the same sqrt(s_NN) and owing to the expected significant uncertainties in yield interpolations which would hinder definite interpretations of nuclear modification factor --R_pPb--, we have derived forward-to-backward and central-to-peripheral yield ratios in which the unknown proton-proton yield cancel. These have been computed without and with a transverse-momentum cut, e.g. to comply with the ATLAS and CMS constraints in the central-rapidity region.

Paper Structure

This paper contains 1 section, 3 equations, 5 figures, 1 table.

Table of Contents

  1. Supplemental material

Figures (5)

  • Figure 1: (Color online) The nuclear modification of the gluon density in a lead nucleus at a scale taken to be the $J/\psi$ mass as obtained with the nDSg set, the envelope of the 30 EPS09 LO sets as well as its central set and 4 specific sets reproducing its envelope for the gluon.
  • Figure 2: (Color online) Illustration of the uncertainties in the prediction of the $J/\psi$ nuclear modification factor in $p$Pb collisions, $R_{p\mathrm{Pb}}$, at $\sqrt{s_{NN}}=5\mathrm{~TeV}$ vs. $y$. (a) effect of the unknown factorisation scale taken to be $(0.75, 1, 2)\times m_T$, (b) central curves from EPS09 at LO and NLO, (c) extremal curves from EPS09 compared to nDSg (same color code as in Fig. 1), (d) effect of the unknown effective $c\bar{c}$ break up cross section for $t_f \gg R_{\rm Pb}$.
  • Figure 3: (Color online) Same as Fig. \ref{['fig:rpPb_uncertainties']} for $R_{\rm FB}$
  • Figure 4: (Color online) Effect of the cut $P_T > 6$ GeV on the $J/\psi$ nuclear modification factor (a & b) and its forward-to-backward ratio (c & d) in $p$Pb collisions at $\sqrt{s_{NN}}=5\mathrm{~TeV}$ versus $y$.
  • Figure 5: (Color online) Central-over-peripheral ratio for 5 sets of EPS09 and nDSg as function of $y$ without (a) and with (b) a $P_T$ cut.