Critical line of 2+1 flavor QCD: Toward the continuum limit

We determine the continuum limit of the curvature of the pseudocritical line of QCD with nf=2+1 staggered fermions at nonzero temperature and quark density. We perform Monte Carlo simulations atimaginary baryon chemical potentials with Highly Improved Staggered Quarks (HISQ), adopting theHISQ/tree action discretization as implemented in the code by the MILC Collaboration. Couplings areadjusted so as to move on a line of constant physics, as determined in Ref. [1], with the strange quark massms fixed at its physical value and a light-to-strange mass ratio ml=ms/20. The chemical potential is setat the same value for the three quark species, μl=μs ≡ μ. We attempt an extrapolation to the continuumusing the results on lattices with temporal size up to Lt = 12. Our estimate for the continuum value of thecurvature κ at zero baryon density, κ = 0.020(4).