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Energy dependence of J/psi absorption in proton-nucleus collisions

Carlos Lourenco, Ramona Vogt, Hermine K. Woehri

TL;DR

The paper demonstrates that normal nuclear absorption of J/psi in proton-nucleus collisions depends strongly on both collision energy and J/psi kinematics when nuclear modifications of parton densities are included. Using the color evaporation model and the Glauber framework with multiple nuclear PDF parametrisations, the authors extract sigma_abs_J/psi across datasets and show its non-universality and sensitivity to initial-state effects. They extrapolate to SPS heavy-ion energies to reassess the baseline absorption, revealing substantial model dependence and urging improved p-A data to sharpen QGP suppression signals. The work highlights the need for multidimensional baselines that incorporate energy, rapidity, and parton-density effects to reliably interpret quarkonium suppression in heavy-ion collisions.

Abstract

Charmonium states are expected to be considerably suppressed in the case of quark-gluon plasma formation in high-energy heavy-ion collisions. However, a robust identification of suppression patterns as signatures of a deconfined QCD medium requires a detailed understanding of the "normal nuclear absorption" already present in proton-nucleus collisions, where the charmonium production cross sections increase less than linearly with the number of target nucleons. We analyse the J/psi production cross sections measured in proton-nucleus collisions in fixed target experiments, with proton beam energies from 200 to 920 GeV, and in d-Au collisions at RHIC, at sqrt(s)=200 GeV, in the framework of the Glauber formalism, using several sets of parton distributions with and without nuclear modifications. The results reveal a significant dependence of the "absorption cross section" on the kinematics of the J/psi and on the collision energy. Extrapolating the observed patterns we derive the level of absorption expected at Elab=158 GeV, the energy at which the heavy-ion data sets were collected at the CERN SPS.

Energy dependence of J/psi absorption in proton-nucleus collisions

TL;DR

The paper demonstrates that normal nuclear absorption of J/psi in proton-nucleus collisions depends strongly on both collision energy and J/psi kinematics when nuclear modifications of parton densities are included. Using the color evaporation model and the Glauber framework with multiple nuclear PDF parametrisations, the authors extract sigma_abs_J/psi across datasets and show its non-universality and sensitivity to initial-state effects. They extrapolate to SPS heavy-ion energies to reassess the baseline absorption, revealing substantial model dependence and urging improved p-A data to sharpen QGP suppression signals. The work highlights the need for multidimensional baselines that incorporate energy, rapidity, and parton-density effects to reliably interpret quarkonium suppression in heavy-ion collisions.

Abstract

Charmonium states are expected to be considerably suppressed in the case of quark-gluon plasma formation in high-energy heavy-ion collisions. However, a robust identification of suppression patterns as signatures of a deconfined QCD medium requires a detailed understanding of the "normal nuclear absorption" already present in proton-nucleus collisions, where the charmonium production cross sections increase less than linearly with the number of target nucleons. We analyse the J/psi production cross sections measured in proton-nucleus collisions in fixed target experiments, with proton beam energies from 200 to 920 GeV, and in d-Au collisions at RHIC, at sqrt(s)=200 GeV, in the framework of the Glauber formalism, using several sets of parton distributions with and without nuclear modifications. The results reveal a significant dependence of the "absorption cross section" on the kinematics of the J/psi and on the collision energy. Extrapolating the observed patterns we derive the level of absorption expected at Elab=158 GeV, the energy at which the heavy-ion data sets were collected at the CERN SPS.

Paper Structure

This paper contains 14 sections, 8 equations, 11 figures, 7 tables.

Table of Contents

  1. Introduction
  2. Brief historical motivation
  3. Basic elements of the calculations
  4. Charmonium production cross sections
  5. Parton densities in the proton and in the nucleus
  6. Charmonium survival probabilities
  7. Measured charmonium production cross sections
  8. Analysis of charmonium nuclear absorption
  9. Cold nuclear matter effects
  10. Extraction of $\sigma_{\rm abs}^{\rm J/\psi}$ from the measurements
  11. Dependence of $\sigma_{\rm abs}^{\rm J/\psi}$ on kinematics
  12. Dependence of $\sigma_{\rm abs}^{\rm J/\psi}$ on the collision energy
  13. Dependence of $\sigma_{\rm abs}^{\rm J/\psi}$ on the J/$\psi$ energy
  14. Summary and outlook

Figures (11)

  • Figure 1: Ratio between the valence quark (left) and the gluon (right) distribution functions in a nucleon of a Pb nucleus and in a free proton, according to several models.
  • Figure 2: Changes induced by the nuclear modifications of the PDFs on the ${c}\bar{c}$ production cross section per nucleon in p-W collisions, using EKS98: as a function of $\sqrt{s_{_{NN}}}$ at $x_{\rm F}=0$ (left) and as a function of $x_{\rm F}$ at four different energies (right).
  • Figure 3: Illustration of the interplay between nuclear modifications of the parton densities and final-state charmonium absorption.
  • Figure 4: The $x_{\mathrm F}$ dependence of the J/$\psi$ and $\psi^\prime$ production ratios, W/Be (left) and Fe/Be (right), per nucleon, measured by E866 at $E_{\rm lab} = 800$ GeV (points) and calculated assuming only nuclear modifications of the parton densities (curves).
  • Figure 5: Illustration of extracting $\sigma_{\rm abs}$ for J/$\psi$ and $\psi^\prime$ production from the E866 W/Be ratio with and without the EKS98 modifications of the PDFs.
  • ...and 6 more figures