The phase structure of QCD: Fluctuations and Correlations

TL;DR

This paper reviews recent advances in understanding the QCD phase diagram, focusing on fluctuations, correlations, and experimental measurements of the quark-gluon plasma and phase transition in high-energy nuclear collisions.

Contribution

It summarizes recent experimental and theoretical progress in mapping the QCD phase diagram and highlights future research opportunities in high-energy nuclear physics.

Findings

Measurements of particle production and fluctuations align with theoretical predictions.

Recent results provide insights into the QCD phase transition and structure.

Future experiments will further explore the QCD phase diagram.

Abstract

The strong interaction - governed by Quantum Chromodynamics (QCD) - shapes the structure of the visible universe. At about 10 $\mu$s after the big bang, the primordial matter made up of quarks and gluons plus leptons, photons and neutrinos, the quark-gluon plasma (QGP), became cool enough to create, in a phase transition, the protons and neutrons of ordinary matter, along with other strongly interacting unstable hadrons. This phase transition was predicted within the framework of QCD and has been studied in accelerator laboratories world-wide since about 40 years. This review will explore recent breakthroughs in the study of the QCD phase diagram. We will highlight measurements of particle production and fluctuations, and compare them to theoretical predictions. We summarize our current understanding of the QCD structure and outline future experimental opportunities with high energy nuclear collisions at fixed-target and collider facilities world-wide.