Higher cumulants of baryon number in critical QCD

TL;DR

This paper investigates higher moments of baryon number near the QCD critical point, showing that kurtosis exhibits a sharp minimum close to the critical point, but the broad minimum observed experimentally is only a precursor, not a signature.

Contribution

It demonstrates that the kurtosis minimum's sharpness is due to the narrow critical region, providing insight into experimental signatures of the QCD critical point.

Findings

Kurtosis attains a sharp minimum near the critical point.

Broad minimum of kurtosis in experiments is a precursor, not a direct signature.

Critical region in chemical potential is very narrow.

Abstract

We study the higher moments of the baryon number in the immediate neighbourhood of the QCD critical endpoint within the framework of Ising-QCD thermodynamics (N.~G. Antoniou {\it et al}, arXiv:1705.09124 [hep-ph]). We show that the kurtosis, as a function of the freeze-out baryon chemical potential, attains a sharp minimum very close to the critical point. We argue that the sharpness of this minimum is due to the narrowness of the critical region in the chemical potential direction. Our analysis reveals that the broad minimum of the kurtosis observed in Au+Au central collisions at STAR (in RHIC-BES I) in the colliding energy region $17$ GeV $< ~\sqrt{s}~<$ $39$ GeV is apparently only a precursor of the critical point and not a signature of its location.