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We present a lattice-QCD-based determination of the chiral phase transition temperature in QCD with two degenerate, massless quarks and a physical strange quark mass using lattice QCD calculations with the highly improved staggered quarks action. We propose and calculate two novel estimators for the chiral transition temperature for several values of the light quark masses, corresponding to Goldstone pion masses in the range of 58MeV ≲ m π ≲ 163MeV. The chiral phase transition temperature is determined by extrapolating to vanishing pion mass using universal scaling analysis. Finite-volume effects are controlled by extrapolating to the thermodynamic limit using spatial lattice extents in the range of 2.8-4.5 times the inverse of the pion mass. Continuum extrapolations are carried out by using three different values of the lattice cutoff, corresponding to lattices with temporal extents Nτ = 6, 8, and 12. After thermodynamic, continuum, and chiral extrapolations, we find the chiral phase transition temperature T0c = 132+3-6MeV. [ABSTRACT FROM AUTHOR]

We report on the first lattice calculation of the QCD phase transition using chiral fermions with physical quark masses. This calculation uses 2 + 1 quark flavors, spatial volumes between (4 fm)3 and (11 fm)3 and temperatures between 139 and 196 MeV. Each temperature is calculated at a single lattice spacing corresponding to a temporal Euclidean extent of Nt = 8. The disconnected chiral susceptibility, χdisc shows a pronounced peak whose position and height depend sensitively on the quark mass. We find no metastability near the peak and a peak height which does not change when a 5 fm spatial extent is increased to 10 fm. Each result is strong evidence that the QCD "phase transition" is not first order but a continuous crossover for w t= 135 MeV. The peak location determines a pseudocritical temperature Tc = 155(1)(8) MeV, in agreement with earlier staggered fermion results. However, the peak height is 50% greater than that suggested by previous staggered results. Chiral SU(2)L × SU(2)R symmetry is fully restored above 164 MeV, but anomalous U(l)A symmetry breaking is nonzero above Tc and vanishes as T is increased to 196 MeV. [ABSTRACT FROM AUTHOR]