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Charmonium Transport in Ultra-Relativistic Heavy-Ion Collisions at the LHC

Biaogang Wu, Ralf Rapp

TL;DR

The paper advances a semi-classical transport description of charmonium in ultra-relativistic heavy-ion collisions by solving a kinetic-rate equation with in-medium binding energies and charm masses, updated charm cross sections, and refined CNM effects. It emphasizes sequential regeneration, whereby $\psi(2S)$ regeneration occurs later in the fireball evolution than $J/\psi$, yielding a higher $\psi(2S)/J/\psi$ ratio and a flow signature shifted to higher $p_T$ for $\psi(2S)$. The approach successfully describes centrality and $p_T$-dependent observables for $J/\psi$ and $\psi(2S)$ in 5.02 TeV Pb-Pb collisions, reconciling regeneration-dominated yields at low $p_T$ with strong primordial suppression at high $p_T$, and aligns with ALICE measurements within uncertainties. These results constrain charm-quark diffusion and in-medium binding properties, and point toward future quantum transport implementations and nonperturbative treatments of quasifree processes with multiple charm pairs.

Abstract

We provide an update on our semi-classical transport approach for quarkonium production in high-energy heavy-ion collisions, focusing on $J/ψ$ and $ψ(2S)$ mesons in 5.02 TeV Pb-Pb collisions at the Large Hadron Collider (LHC) at both forward and mid-rapidity. In particular, we employ the most recent charm-production cross sections reported in pp collisions, which are pivotal for the magnitude of the regeneration contribution, and their modifications due to cold-nuclear-matter (CNM) effects. Multi-differential observables are calculated in terms of nuclear modification factors as a function of centrality, transverse momentum, and rapidity, including the contributions from bottom-decay feeddown. For our predictions for $ψ(2S)$ production, the mechanism of sequential regeneration relative to the more strongly bound $J/ψ$ meson plays an important role in interpreting recent ALICE data.

Charmonium Transport in Ultra-Relativistic Heavy-Ion Collisions at the LHC

TL;DR

The paper advances a semi-classical transport description of charmonium in ultra-relativistic heavy-ion collisions by solving a kinetic-rate equation with in-medium binding energies and charm masses, updated charm cross sections, and refined CNM effects. It emphasizes sequential regeneration, whereby regeneration occurs later in the fireball evolution than , yielding a higher ratio and a flow signature shifted to higher for . The approach successfully describes centrality and -dependent observables for and in 5.02 TeV Pb-Pb collisions, reconciling regeneration-dominated yields at low with strong primordial suppression at high , and aligns with ALICE measurements within uncertainties. These results constrain charm-quark diffusion and in-medium binding properties, and point toward future quantum transport implementations and nonperturbative treatments of quasifree processes with multiple charm pairs.

Abstract

We provide an update on our semi-classical transport approach for quarkonium production in high-energy heavy-ion collisions, focusing on and mesons in 5.02 TeV Pb-Pb collisions at the Large Hadron Collider (LHC) at both forward and mid-rapidity. In particular, we employ the most recent charm-production cross sections reported in pp collisions, which are pivotal for the magnitude of the regeneration contribution, and their modifications due to cold-nuclear-matter (CNM) effects. Multi-differential observables are calculated in terms of nuclear modification factors as a function of centrality, transverse momentum, and rapidity, including the contributions from bottom-decay feeddown. For our predictions for production, the mechanism of sequential regeneration relative to the more strongly bound meson plays an important role in interpreting recent ALICE data.
Paper Structure (14 sections, 20 equations, 19 figures, 1 table)

This paper contains 14 sections, 20 equations, 19 figures, 1 table.

Table of Contents

  1. Introduction
  2. Kinetic Approach
  3. Transport Parameters
  4. Charmonium Reaction Rates
  5. Charmonium equilibrium limits
  6. Initial Conditions and Medium Evolution
  7. Time and Centrality Dependence of Charmonium Yields at the LHC
  8. Time evolution of charmonium yields
  9. Centrality dependence
  10. Transverse-Momentum Spectra
  11. Initial $p_{\rm T}$ spectra and their suppression in heavy-ion collisions
  12. Transverse-momentum spectra from regeneration
  13. Comparison to experimental $p_{\rm T}$ spectra
  14. Conclusions

Figures (19)

  • Figure S1: Charm-quark mass (left panel) and charmonium binding energies (right panel) as a function of temperature.
  • Figure S2: Dissociation rates of charmonia in the medium as a function of momentum at different temperatures (left panel) and temperature at $p$=0 and $3\,{\rm GeV}/c$ (right panel).
  • Figure S3: Gluo-dissociation rates of charmonia in the QGP as a function of momentum (left panel) for three different temperatures and as a function of temperature at $p=0$ (right panel) where they are also compared to the quasifree rates.
  • Figure S4: Our parameterizations of the suppression of the $c\bar{c}$ production cross section due to nuclear shadowing of the parton distribution functions, as a function of $p_{\rm T}$ (left panel) in p-Pb collisions in terms of the product at forward and backward rapidities and compared to ALICE data ALICE:2015sru, and versus $N_{\rm part}$ in Pb-Pb collisions (right panel).
  • Figure S5: Fraction of bottom-hadron decay feeddown to inclusive $J/\psi$ production as measured by ALICE, ATLAS and CMS in pp collisions at the LHC Andronic:2015wma; our functional fit is shown by the solid line.
  • ...and 14 more figures