Fluctuations of conserved charges in relativistic heavy ion collisions: An introduction

TL;DR

This paper introduces the study of fluctuations of conserved charges in relativistic heavy ion collisions, emphasizing their significance in understanding the properties of the hot medium and recent experimental and theoretical advances.

Contribution

It provides a pedagogical overview of fluctuation physics in heavy ion collisions, including recent developments and the role of non-Gaussian fluctuations.

Findings

Discussion of cumulants and fluctuation concepts

Analysis of non-Gaussian fluctuation phenomena

Survey of experimental and theoretical progress

Abstract

Bulk fluctuations of conserved charges measured by event-by-event analysis in relativistic heavy ion collisions are observables which are believed to carry significant amount of information on the hot medium created by the collisions. Active studies have been done recently experimentally, theoretically, and on the lattice. In particular, non-Gaussianity of the fluctuations has acquired much attention recently. In this review, we give a pedagogical introduction to these issues, and survey recent developments in this field of research. Starting from the definition of cumulants, basic concepts in fluctuation physics, such as thermal fluctuations in statistical mechanics and time evolution of fluctuations in diffusive systems, are described. Phenomena which are expected to occur in finite temperature and/or density QCD matter and their measurement by event-by-event analyses are also elucidated.