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

Abstract

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 µ 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 (0)) 4 , we determined κ X 2 and κ X 4 from Taylor expansions of chiral observables in µ 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., µ S (T, µ B ) and µ Q (T, µ B ) fixed from strangeness-neutrality and isospin-imbalance, we found κ B 2 =0.012(4) and κ B 4 =0.000(4). For µ B 300 MeV, the chemical freeze-out takes place in the vicinity of the QCD phase 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 .

Finite-density QCD transition in a magnetic background field

“…In the zero-field limit, our data converge well to the known result T ch c = 156.5(1.5) MeV of Ref. [4], shown by the red square in Fig. 5(a).…”

Baryon number fluctuations in the QCD phase diagram from Dyson-Schwinger equations

“…We find T (χ2) c = 153 MeV, which is only slightly lower than the value from the inflection point of the subtracted condensate determined in the previous section to 156 MeV. Note again that there is no unique definition of the critical temperature due to the crossover nature of the transition and both values are in agreement with lattice QCD [6,7,10,11,89].…”

“…At zero chemical potential, there is firm evidence from lattice QCD for an analytic crossover from a low-temperature phase characterized by chiral symmetry breaking to a high-temperature (partially) chirally restored phase [4][5][6][7][8][9]. The corresponding pseudocritical temperature has been localized at T c ≈ 156 MeV within a definition-dependent range of several MeV [6,7,10,11]. However, the situation is much less clear at (real) chemical potential, where lattice calculations are hampered by the notorious fermion sign problem.…”

A Study of the Properties of the QCD Phase Diagram in High-Energy Nuclear Collisions

“…Figure 1 summarizes the current status of the studies. At the zero baryonic density, the transition from QGP to hadronic matter is a smooth-crossover at T = 150 − 160 MeV [5][6][7][8][9], see dashed-line in the figure. These results are extracted from the state of the art Lattice gauge theory calculations.…”

“…[12]. The dashed-line near µ B = 0 indicates the crossover transition from the Quark-Gluon-Plasma to Hadron Gas [5][6][7][8][9]. The solid-line and the square show the expected 1st-order phase boundary and its end point: critical point.…”