The QCD transition temperature: results with physical masses in the continuum limit

TL;DR

This study determines the QCD transition temperature using lattice simulations with physical quark masses, revealing that different observables yield varying $T_c$ values due to the crossover nature of the transition.

Contribution

First continuum-extrapolated lattice QCD results for $T_c$ with physical quark masses using improved actions, highlighting observable-dependent $T_c$ values.

Findings

$T_c$ from chiral susceptibility: 151(3)(3) MeV

$T_c$ from strange quark susceptibility: 24(4) MeV higher

$T_c$ from Polyakov loops: 25(4) MeV higher

Abstract

The transition temperature ($T_c$) of QCD is determined by Symanzik improved gauge and stout-link improved staggered fermionic lattice simulations. We use physical masses both for the light quarks ($m_{ud}$) and for the strange quark ($m_s$). Four sets of lattice spacings ($N_t$=4,6,8 and 10) were used to carry out a continuum extrapolation. It turned out that only $N_t$=6,8 and 10 can be used for a controlled extrapolation, $N_t$=4 is out of the scaling region. Since the QCD transition is a non-singular cross-over there is no unique $T_c$. Thus, different observables lead to different numerical $T_c$ values even in the continuum and thermodynamic limit. The peak of the renormalized chiral susceptibility predicts $T_c$=151(3)(3) MeV, wheres $T_c$-s based on the strange quark number susceptibility and Polyakov loops result in 24(4) MeV and 25(4) MeV larger values, respectively. Another consequence of the cross-over is the non-vanishing width of the peaks even in the thermodynamic limit, which we also determine. These numbers are attempted to be the full result for the $T$$\neq$0 transition, though other lattice fermion formulations (e.g. Wilson) are needed to cross-check them.