Exploring the QCD phase diagram through correlations and fluctuations

TL;DR

This review discusses how fluctuations and correlations serve as key probes to explore the QCD phase diagram, emphasizing recent experimental and theoretical advances, especially at high baryon density, and outlining future research directions.

Contribution

It provides a comprehensive overview of fluctuation and correlation measurements as tools to identify phase transitions and the critical point in the QCD phase diagram, integrating recent experimental data and theoretical insights.

Findings

Cumulants of conserved charges are promising signatures of phase transitions.

Experimental results from STAR at RHIC support theoretical predictions.

Future experiments like CBM will further explore the QCD phase structure.

Abstract

The exploration of the Quantum Chromodynamics (QCD) phase diagram is a central goal of relativistic heavy-ion collision experiments. This review focuses on the role of fluctuations and correlations as sensitive probes of the phase structure. We discuss theoretical advancements and experimental methodologies employed to map the QCD phase diagram, highlighting constraints derived from both lattice QCD calculations and existing experimental data. Key observables such as cumulants and factorial cumulants of conserved charges (e.g., net-proton, net-charge) are explored as promising signatures of phase transitions and the QCD critical point. We discuss how these quantities are measured experimentally and compared with theoretical predictions, addressing challenges and best practices for meaningful comparisons. Special attention is given to predictions and current experimental results at high baryon density, including recent findings from the STAR collaboration at RHIC. Finally, we identify open issues and future directions for fluctuation and correlation studies at lower collision energies, relevant for future measurements, for example by the CBM experiment.