QCD deconfinement transition line up to μ_B = 400 MeV from finite volume lattice simulations

¹ Department of Physics, Wuppertal University, Gaussstr. 20, D-42119, Wuppertal, Germany
² Pennsylvania State University, Department of Physics, State College, PA 16801, USA
³ Institute for Theoretical Physics, ELTE Eötvös Loránd University, Pázmány P. sétány 1/A, H-1117 Budapest, Hungary
⁴ Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52425 Jülich, Germany
⁵ Dipartimento di Fisica, Università di Torino and INFN Torino, Via P. Giuria 1, I-10125 Torino, Italy

Published online: 17 April 2026

Abstract

The QCD cross-over line in the temperature (T) - baryo-chemical potential (μ_B) plane has been computed by several lattice groups by calculating the chiral order parameter and its susceptibility at finite values of μ_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,μ_B)) in T, which is based on the renormalized Polyakov loop. We extrapolate S_Q(T,μ_B) based on high statistics finite temperature ensembles on a 16³ × 8 lattice to finite density by means of a Taylor expansion to eighth order in μ_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 phenomeno-logical 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 μ_B ≈ 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 μ_B. This work is based on Ref. [1].