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

Abstract

We determine the continuum limit of the curvature of the pseudocritical line of QCD with $n_f$=2+1 staggered fermions at nonzero temperature and quark density. We perform Monte Carlo simulations at imaginary baryon chemical potentials, adopting the HISQ/tree action discretization, as implemented in the code by the MILC collaboration. Couplings are adjusted so as to move on a line of constant physics, as determined in Ref.~\cite{Bazavov:2011nk}, with the strange quark mass $m_s$ fixed at its physical value and a light-to-strange mass ratio $m_l/m_s=1/20$. The chemical potential is set at the same value for the three quark species, $\hat{I}{¼}_l=\hat{I}{¼}_s\equiv \hat{I}¼$. We attempt an extrapolation to the continuum using the results on lattices with temporal size up to $L_t=12$. Our estimate for the continuum value of the curvature $\hat{I}º$ at zero baryon density, $\hat{I}º=0.020(4)$, is compared with recent lattice results and with experimental determinations of the freeze-out curve.

10 pages, 4 figures, 16 tables; modified title and abstract, added two tables and a few comments in the text, added appendix with 13 tables; version to appear on Phys. Rev. D