The QCD crossover at zero and non-zero baryon densities from Lattice QCD

Abstract

We map out the QCD crossover line Tc(μB)Tc(0)=1−κ2(μBTc(0))2−κ4(μBTc(0))+O(μB6) for the first time up to O(μB4) for a strangeness neutral system by performing a Taylor expansion of chiral observables in temperature T and chemical potentials μ. At vanishing chemical potential, we report a crossover temperature Tc(0)=(156.5±1.5)MeV defined by the average of several second-order chiral susceptibilities. For a system with thermal conditions appropriate for a heavy-ion collision, we determined a curvature from the subtracted condensate as κ2=0.0120(20) and from the disconnected susceptibility as κ2=0.0123(30). The next order κ4 is significantly smaller. We also report the crossover temperature as a function of the chemical potentials for: baryon-number, electric charge, strangeness and isospin. Additionally, we find that Tc(μB) is in agreement with lines of constant energy density and constant entropy density. Along this crossover line, we study net baryon-number fluctuations and show that their increase is substantially smaller compared to that obtained in HRG model calculations. Similarly, we analyze chiral susceptibility fluctuations along the crossover line and show that these are constant. We conclude that no signs for a narrowing of the crossover region can be found for baryon chemical potential μB<250MeV.