Bulk thermodynamics and charge fluctuations at non-vanishing baryon density

TL;DR

This study uses lattice QCD calculations to analyze bulk thermodynamics and charge fluctuations at non-zero baryon density, revealing significant fluctuations near the transition temperature and effects of strangeness constraints.

Contribution

First lattice QCD analysis with improved actions to control cut-off effects at non-zero density, providing insights into fluctuations relevant for heavy ion collisions.

Findings

Large net baryon number and strangeness fluctuations near transition temperature.

Strangeness fluctuations are enhanced at finite baryon density.

Strangeness fluctuations decrease when strangeness is constrained to vanish.

Abstract

We present results on bulk thermodynamic quantities as well as net baryon number, strangeness and electric charge fluctuations in QCD at non-zero density and temperature obtained from lattice calculations with almost physical quark masses for two values of the lattice cut-off $aT=1/4$ and 1/6 . We show that with our improved p4fa3-action the cut-off effects are under control when using lattices with a temporal extent of 6 or larger and that the contribution to the equation of state, which is due to a finite chemical potential is small for $\mu_q/T<1$. Moreover, at vanishing chemical potential, i.e. under conditions almost realized at RHIC and the LHC, quartic fluctuations of net baryon number and strangeness are large in a narrow temperature interval characterizing the transition region from the low to high temperature phase. At non-zero baryon number density, strangeness fluctuations are enhanced and correlated to fluctuations of the net baryon number. If strangeness is furthermore forced to vanish, as it may be the case in systems created in heavy ion collisions, strangeness fluctuations are significantly smaller than baryon number fluctuations.