Hard Probes of the Quark Gluon Plasma in Heavy Ion Collisions

TL;DR

This paper reviews how high-energy nuclear collision experiments at RHIC and LHC have advanced understanding of the quark-gluon plasma through phenomena like jet quenching and quarkonia melting, highlighting new insights and theoretical challenges.

Contribution

It synthesizes recent experimental results from RHIC and LHC, emphasizing the need for new theoretical models of jets in a medium and updating concepts of hot QCD matter.

Findings

Jet quenching confirmed at RHIC and LHC

Quarkonia melting provides temperature estimates

New data challenges existing jet theories

Abstract

The medium-modifications of processes characterized by the presence of a hard scale provide the most diverse tools to characterize the properties of the matter created in high-energy nuclear collisions. Indeed, jet quenching, the suppression of particles produced at high transverse momentum, has been established at RHIC almost a decade ago as one of the main tools in heavy-ion collisions. The melting of quarkonia is expected to provide also information about the temperature and the properties of the produced medium. The beginning of the LHC era for hot QCD studies starts with the first nuclear beams in 2010. The amount of information produced by this first run is overwhelming: The three experiments with nuclear program (ALICE, ATLAS and CMS) have provide new results in basically all subjects considered in previous experiments and have also shown the potential to make nuclear collisions at the TeV scale for the first time. I will review what the results from both RHIC and LHC imply for our understanding of hot and dense QCD matter from a theorists' perspective and how these new results change some of the concepts we developed in the last years. Particular attention is devoted to the case of jets, as the first data recently published from the LHC and the limitations of previous approaches call for a new theory of jets in a medium.