Curvature of the freeze-out line in heavy ion collisions

Bazavov A, Ding H-T, Hegde P, et al. Curvature of the freeze-out line in heavy ion collisions. Physical Review D. 2016;93(1): 014512.We calculate the mean and variance of net-baryon number and net-electric charge distributions from quantum chromodynamics (QCD) using a next-to-leading order Taylor expansion in terms of temperature and chemical potentials. We compare these expansions with experimental data from STAR and PHENIX, determine the freeze-out temperature in the limit of vanishing baryon chemical potential, and, for the first time, constrain the curvature of the freeze-out line through a direct comparison between experimental data on net-charge fluctuations and a QCD calculation. We obtain a bound on the curvature coefficient, kappa(f)(2) < 0.011, that is compatible with lattice QCD results on the curvature of the QCD transition line