Equation of State and the Finite Temperature Transition in QCD

TL;DR

This paper summarizes the HotQCD collaboration's findings on the QCD equation of state and crossover transition, highlighting thermodynamic quantities and the simultaneous occurrence of deconfinement and chiral symmetry restoration around 150-160 MeV.

Contribution

First comprehensive lattice QCD study of thermodynamic properties and transition signals using improved staggered fermions at physical quark masses.

Findings

Deconfinement and chiral symmetry restoration occur in a narrow temperature range.

Thermodynamic quantities like energy density and pressure are characterized over 140-540 MeV.

Results are consistent across different lattice sizes and fermion actions.

Abstract

This talk provides a summary of the results obtained by the HotQCD collaboration on the equation of state and the crossover transition in 2+1 flavor QCD. We investigate bulk thermodynamic quantities - energy density, pressure, entropy density, and the speed of sound over the temperature range 140 < T < 540 MeV. These results have been obtained on lattices of temporal size N_tau = 6 and 8 and with two improved staggered fermion actions, asqtad and p4. Our most extensive results are with masses of the two degenerate light quarks set at m_l = 0.1 m_s corresponding to the Goldstone pion mass m_pi between 220-260 MeV. In these simulations, the strange quark mass is tuned to its physical value and constant values of m_l/m_s define lines of constant physics. We also summarize the current state of results on observables sensitive to the chiral and deconfining physics -- the light and strange quark number susceptibilities, the chiral condensate and its susceptibility, and the renormalized Polyakov loop. Our results indicate that the deconfinement and chiral symmetry restoration occur in the same narrow temperature interval.