The QCD Equation of State with almost Physical Quark Masses

TL;DR

This study computes the QCD equation of state with near-physical quark masses using lattice simulations, providing detailed thermodynamic data across a wide temperature range and analyzing finite cut-off effects.

Contribution

It offers the first high-precision lattice QCD results for the equation of state with almost physical quark masses at multiple lattice spacings and includes an analysis of cut-off effects at high temperatures.

Findings

Thermodynamic observables are computed for 140-800 MeV temperatures.

Finite cut-off effects are significant above twice the transition temperature.

Zero temperature observables are used to set the temperature scale and study deconfinement and chiral symmetry restoration.

Abstract

We present results on the equation of state in QCD with two light quark flavors and a heavier strange quark. Calculations with improved staggered fermions have been performed on lattices with temporal extent Nt =4 and 6 on a line of constant physics with almost physical quark mass values; the pion mass is about 220 MeV, and the strange quark mass is adjusted to its physical value. High statistics results on large lattices are obtained for bulk thermodynamic observables, i.e. pressure, energy and entropy density, at vanishing quark chemical potential for a wide range of temperatures, 140 MeV < T < 800 MeV. We present a detailed discussion of finite cut-off effects which become particularly significant for temperatures larger than about twice the transition temperature. At these high temperatures we also performed calculations of the trace anomaly on lattices with temporal extent Nt=8. Furthermore, we have performed an extensive analysis of zero temperature observables including the light and strange quark condensates and the static quark potential at zero temperature. These are used to set the temperature scale for thermodynamic observables and to calculate renormalized observables that are sensitive to deconfinement and chiral symmetry restoration and become order parameters in the infinite and zero quark mass limits, respectively.