Charmed signatures for phase transitions in heavy-ion collisions

TL;DR

This paper investigates charmonium production and suppression in heavy-ion collisions at different energies, comparing models to experimental data, and finds evidence for a deconfined quark-gluon plasma at RHIC energies.

Contribution

It compares hadronic and QGP melting models for charmonium suppression across energies, highlighting the need for a theory with strongly interacting quarks and gluons at RHIC.

Findings

Comover absorption model better at 158 AGeV

Neither model fully explains 200 GeV data

Deconfined phase reached at RHIC

Abstract

The interplay of charmonium production and suppression in In+In and Pb+Pb reactions at 158 AGeV and in Au+Au reactions at sqrt(s)=200 GeV is investigated with the HSD transport approach within the `hadronic comover model' and the `QGP melting scenario'. The results for the J/Psi suppression and the Psi' to J/Psi ratio are compared to the recent data of the NA50, NA60, and PHENIX Collaborations. We find that, at 158 AGeV, the comover absorption model performs better than the scenario of abrupt threshold melting. However, neither interaction with hadrons alone nor simple color screening satisfactory describes the data at sqrt(s)=200 GeV. A deconfined phase is clearly reached at RHIC, but a theory having the relevant degrees of freedom in this regime (strongly interacting quarks/gluons) is needed to study its transport properties.