Baryon number fluctuations and QCD phase structure

TL;DR

This paper explores the QCD phase structure and baryon number fluctuations using the PNJL model, highlighting the importance of the critical end point and higher moments of conserved charges for understanding phase transitions.

Contribution

It demonstrates how baryon number fluctuations and the coincidence or separation of chiral and deconfinement transitions reveal the QCD phase structure, emphasizing the role of the critical end point.

Findings

The chiral and deconfinement transitions influence baryon number fluctuations.

The existence of a critical end point explains non-monotonic kurtosis behavior.

Higher moments of conserved charges are effective probes of QCD criticality.

Abstract

We investigate the phase structure of strongly interacting matter and baryon number fluctuations in the Polyakov loop improved Nambu--Jona-Lasinio (PNJL) model. The calculation shows that both the chiral and deconfinement transitions, as well as their coincidence and separation determine the basic QCD phase structure. The contour maps and the three-dimensional diagrams of the net-baryon kurtosis and skewness present well the trace of QCD phase structure. Comparing with the experimental data, we find that the existence of a critical end point (CEP) of chiral transition is crucial to explain the non-monotonic energy dependence and the large deviation from Poisson baseline of net-proton kurtosis. In particular, the relation between the chiral and deconfinement transitions in the crossover region is also reflected by the baryon number fluctuations. This study shows that the measurements of higher moments of multiplicity distributions of conserved charges are powerful to investigate the criticality and even the chiral and deconfinement transitions in the crossover region.