Equation of state and QCD transition at finite temperature

TL;DR

This study computes the QCD equation of state at finite temperature using improved lattice techniques, confirming the simultaneous occurrence of deconfinement and chiral symmetry restoration, and provides a parametrization for hydrodynamic models.

Contribution

It presents new lattice QCD calculations of the equation of state with physical quark masses and improved actions, including a parametrization with uncertainty estimates.

Findings

Deconfinement and chiral restoration occur in a narrow temperature range.

Good agreement between different improved staggered fermion actions.

Systematic errors estimated at about 10 MeV.

Abstract

We calculate the equation of state in 2+1 flavor QCD at finite temperature with physical strange quark mass and almost physical light quark masses using lattices with temporal extent Nt=8. Calculations have been performed with two different improved staggered fermion actions, the asqtad and p4 actions. Overall, we find good agreement between results obtained with these two O(a^2) improved staggered fermion discretization schemes. A comparison with earlier calculations on coarser lattices is performed to quantify systematic errors in current studies of the equation of state. We also present results for observables that are sensitive to deconfining and chiral aspects of the QCD transition on Nt=6 and 8 lattices. We find that deconfinement and chiral symmetry restoration happen in the same narrow temperature interval. In an Appendix we present a simple parametrization of the equation of state that can easily be used in hydrodynamic model calculations. In this parametrization we also incorporated an estimate of current uncertainties in the lattice calculations which arise from cutoff and quark mass effects. We estimate these systematic effects to be about 10 MeV