Critical line of2+1flavor QCD

Abstract

We determine the curvature of the (pseudo)critical line of QCD with ${n}_{f}\text{ }=\text{ }2\text{ }+\text{ }1$ staggered fermions at nonzero temperature and quark density by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed by adopting the highly improved staggered quarks /tree action discretization, as implemented in the code by the MILC Collaboration, suitably modified to include a nonzero imaginary baryon chemical potential. We work on a line of constant physics, as determined in Ref. [1], adjusting the couplings so as to keep the strange quark mass ${m}_{s}$ fixed at its physical value, with a light to strange mass ratio of ${m}_{l}/{m}_{s}=1/20$. In the present investigation, we set the chemical potential at the same value for the three quark species, ${\ensuremath{\mu}}_{l}={\ensuremath{\mu}}_{s}\ensuremath{\equiv}\ensuremath{\mu}$. We explore lattices of different spatial extensions, ${16}^{3}\ifmmode\times\else\texttimes\fi{}6$ and ${24}^{3}\ifmmode\times\else\texttimes\fi{}6$, to check for finite size effects, and present results on a ${32}^{3}\ifmmode\times\else\texttimes\fi{}8$ lattice, to check for finite cutoff effects. We discuss our results for the curvature $\ensuremath{\kappa}$ of the (pseudo)critical line at $\ensuremath{\mu}=0$, which indicate $\ensuremath{\kappa}=0.018(4)$, and compare them with previous lattice determinations by alternative methods and with experimental determinations of the freeze-out curve.