Hard Probes in Heavy-Ion Physics

TL;DR

This paper reviews how high transverse momentum processes, or 'hard probes', are modified by the quark-gluon plasma in ultrarelativistic heavy-ion collisions, providing insights into the properties of hot, dense QCD matter.

Contribution

It summarizes recent developments in understanding the interaction of hard probes with the quark-gluon plasma in heavy-ion physics.

Findings

Evidence of thermalized bulk medium in heavy-ion collisions

Modification patterns of high-$P_T$ particles observed

Progress in modeling hard probe interactions with QCD matter

Abstract

The aim of ultrarelativistic heavy ion physics is to study collectivity and thermodynamics of Quantum Chromodynamics (QCD) by creating a transient small volume of matter with extreme density and temperature. There is experimental evidence that most of the particles created in such a collision form indeed a thermalized system characterized by collective response to pressure gradients. However, a numerically small subset of high transverse momentum ($P_T$) processes takes place independent of the bulk, with the outgoing partons subsequently propagating through the bulk medium. Understanding the modification of such 'hard probes' by the bulk medium is an important part of the efforts to determine the properties of hot and dense QCD matter. In this paper, current developments are reviewed.