Charmonium dissociation and recombination at RHIC and LHC

TL;DR

The paper extends the comovers interaction model to include recombination of charm quarks into J/psi, with no new free parameters, and provides a comprehensive treatment of initial-state effects (shadowing, nuclear absorption, energy-momentum conservation) and final-state interactions with comovers. At RHIC energies, recombination is essential to reproduce the centrality and rapidity dependence of J/psi suppression in Au+Au and Cu+Cu collisions; open-charm yields from pp data set the recombination strength. Predictions for Pb+Pb at the LHC show that, even with enhanced charm production, suppression remains substantial due to strong shadowing and comovers effects, though the magnitude of recombination depends on the uncertain charm cross section. The work highlights the importance of pp charm measurements for constraining heavy-ion predictions and provides a framework that avoids assuming thermal equilibrium. Overall, the CIM with recombination offers a cohesive, parameter-light description of charmonium dynamics from RHIC to LHC.

Abstract

Charmonium production at heavy-ion colliders is considered within the comovers interaction model. The formalism is extended by including possible secondary J/psi production through recombination and an estimate of recombination effects is made with no free parameters involved. The comovers interaction model also includes a comprehensive treatment of initial-state nuclear effects, which are discussed in the context of such high energies. With these tools, the model properly describes the centrality and the rapidity dependence of experimental data at RHIC energy, $\sqrt{s}$ = 200 GeV, for both Au+Au and Cu+Cu collisions. Predictions for LHC, $\sqrt{s}$ = 5.5 TeV, are presented and the assumptions and extrapolations involved are discussed.

Figures (3)

• Figure 1: Results for $J/\psi$ suppression in Au+Au at RHIC ($\sqrt{s} = 200$ GeV) at mid- (left figure), and at forward rapidities (right figure). Data are from PHENIX07. The solid curves are the final results. The dashed-dotted ones are the results without recombination ($C = 0$). The dashed line is the total initial-state effect. The dotted line in the right figure is the result of shadowing. In the left figure the last two lines coincide (see main text).
• Figure 2: Results for $J/\psi$ suppression in Cu+Cu at RHIC ($\sqrt{s} = 200$ GeV), at mid- (left) and at forward rapidities (right). For details, see caption of Fig. \ref{['fig:JPSIresultsRHICAuAu']}. Data are from Cianciolo05.
• Figure 3: Results for $J/\psi$ suppression in Pb+Pb at LHC ($\sqrt{s} = 5.5$ TeV) at mid-rapidities for different values of the parameter $C$. The upper line is the suppression due to initial-state effects (shadowing).