QCD under extreme conditions

TL;DR

This paper reviews the properties and experimental signatures of the Quark-Gluon Plasma created in high-energy nucleus collisions, discussing phase transitions, fluctuations, transport properties, and probes of deconfinement.

Contribution

It provides a comprehensive overview of the current understanding of QGP properties, connecting experimental data with theoretical models and lattice QCD results.

Findings

QGP behaves as a nearly ideal fluid with measurable viscosities.

Fluctuations of conserved charges relate to the chiral phase transition.

Parton energy loss and quarkonia serve as probes of deconfinement.

Abstract

In nucleus-nucleus collisions at relativistic energies a new kind of matter is created, the Quark-Gluon Plasma (QGP). The phase diagram of such matter and the chemical freeze-out points will be presented in connection to the pseudo-critical temperature for the chiral cross over transition. The role of conserved charge fluctuations to give experimental access to the nature of the chiral phase transition will be summarized in terms of the relation to lattice QCD and the current experimental data. The QGP can be characterized as a nearly ideal liquid expanding hydrodynamically and the experimental data allow to extract transport parameters such as the bulk and shear viscosities. The energy loss of partons in the QGP probes the high parton density of the medium. The role of quarkonia and open charm hadrons as a probe of deconfinement and hadronization form the final topic.