Baryon number and charge fluctuations from lattice QCD

TL;DR

This study uses lattice QCD to compute electric and baryonic charge fluctuations, revealing universal scaling behavior near the QCD critical point and providing results that can connect theoretical transition temperatures with experimental freeze-out temperatures.

Contribution

It presents lattice QCD calculations of charge fluctuations with improved quark actions, demonstrating universal scaling laws and offering volume-independent ratios for experimental comparison.

Findings

Higher order cumulants show universal scaling behavior.

Cumulant ratios are volume independent and comparable to experiments.

Results differ from hadron resonance gas model predictions.

Abstract

We calculate electric and baryonic charge fluctuations on the lattice. Results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with spacial extent of $N_\tau=6,8,12$. Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which is arising due to a critical point of QCD in the chiral limit. Considering cumulants up to the sixth order, we observe that they generically behave as expected from universal scaling laws, which is quite different from the cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. Such a comparison will unambiguously relate the QCD transition temperature that has been determined on the lattice with the freeze out temperature of heavy ion collision at LHC and RHIC.