Chiral crossover in QCD at zero and non-zero chemical potentials HotQCD Collaboration

We present results for pseudo-critical temperatures of QCD chiral crossovers at zero and non-zero values of baryon (B), strangeness (S), electric charge (Q), and isospin (I) chemical potentials mu(X=B,Q,S,I). The results were obtained using lattice QCD calculations carried out with two degenerate up and down dynamical quarks and a dynamical strange quark, with quark masses corresponding to physical values of pion and kaon masses in the continuum limit. By parameterizing pseudo-critical temperatures as T-c(mu(x)) = T-c(0)[1-kappa(X)(2)(mu(X)/T-c(0))(2) - kappa(X)(4)(mu(X)/T-c(0))(4)], we determined kappa(X)(2) and kappa(X)(4) from Taylor expansions of chiral observables in mu(X). We obtained a precise result for T-c(0) = (156.5 +/- 1.5) MeV. For analogous thermal conditions at the chemical freeze-out of relativistic heavy-ion collisions, i.e., mu(S)(T, mu(B)) and mu(Q)(T, mu(B)) fixed from strangeness-neutrality and isospin-imbalance, we found kappa(B)(2) = 0.012(4) and kappa(B)(4) = 0.000(4). For mu(B) less than or similar to 300 MeV, the chemical freeze-out takes place in the vicinity of the QCD phase 4 boundary, which coincides with the lines of constant energy density of 0.42(6) GeV/fm(3) and constant entropy density of 3.7(5) fm(-3). (C) 2019 The Author(s). Published by Elsevier B.V.