Fluidity and supercriticality of the QCD matter created in relativistic heavy ion collisions

TL;DR

This paper explores the fluidity and potential supercritical state of QCD matter in heavy ion collisions, proposing a new measure of fluidity, and predicts enhanced fluidity at higher energies like LHC, with implications for hydrodynamic modeling.

Contribution

It introduces a universal fluidity measure for critical fluids, suggests QCD matter may be supercritical, and links supercriticality to observed fluidity in heavy ion collisions.

Findings

Supercritical QCD matter has enhanced fluidity.

Predicted better fluidity at LHC energies.

Fluidity decreases at lower beam energies.

Abstract

In this paper we discuss the fluidity of the hot and dense QCD matter created in ultrarelativistic heavy ion collisions in comparison with various other fluids, and in particular suggest its possible supercriticality. After examining the proper way to compare non-relativistic and relativistic fluids from both thermodynamic and hydrodynamic perspectives, we propose a new fluidity measure which shows certain universality for a remarkable diversity of critical fluids. We then demonstrate that a fluid in its supercritical regime has its fluidity considerably enhanced. This may suggest a possible relationship between the seemingly good fluidity of the QCD matter produced in heavy ion collisions at center of mass energy of $\sqrt{s}=200 \rm AGeV$ and the supercriticality of this matter with respect to the Critical-End-Point on the QCD phase diagram. Based on such observation, we predict an even better fluidity of the matter to be created in heavy ion collisions at LHC energy and the loss of good fluidity at certain lower beam energy. Finally based on our criteria, we analyze the suitability of a hydrodynamic description for the fireball evolution in heavy ion collisions at various energies.