QCD deconfinement transition line up to $\mu_B=400$ MeV from finite volume lattice simulations

TL;DR

This study uses lattice QCD simulations to map the deconfinement transition line up to $rac{400}{MeV}$ in baryon chemical potential, revealing a broadening of the transition and no critical endpoint within this range.

Contribution

It provides the first high-precision lattice determination of the deconfinement transition line at finite density using a Taylor expansion up to eighth order.

Findings

Deconfinement temperature aligns with heavy ion collision freeze-out estimates.

The transition broadens with increasing chemical potential up to 400 MeV.

No evidence of a critical endpoint within the studied range.

Abstract

The QCD cross-over line in the temperature ($T$) -- baryo-chemical potential ($\mu_B$) plane has been computed by several lattice groups by calculating the chiral order parameter and its susceptibility at finite values of $\mu_B$. In this work we focus on the deconfinement aspect of the transition between hadronic and Quark Gluon Plasma (QGP) phases. We define the deconfinement temperature as the peak position of the static quark entropy ($S_Q(T,\mu_B)$) in $T$, which is based on the renormalized Polyakov loop. We extrapolate $S_Q(T,\mu_B)$ based on high statistics finite temperature ensembles on a $16^3\times 8$ lattice to finite density by means of a Taylor expansion to eighth order in $\mu_B$ (NNNLO) along the strangeness neutral line. For the simulations the 4HEX staggered action was used with 2+1 flavors at physical quark masses. In this setup the phase diagram can be drawn up to unprecedentedly high chemical potentials. Our results for the deconfinement temperature are in rough agreement with phenomenological estimates of the freeze-out curve in relativistic heavy ion collisions. In addition, we study the width of the deconfinement crossover. We show that up to $\mu_B \approx 400$ MeV, the deconfinement transition gets broader at higher densities, disfavoring the existence of a deconfinement critical endpoint in this range. Finally, we examine the transition line without the strangeness neutrality condition and observe a hint for the narrowing of the crossover towards large $\mu_B$.