On the critical line of 2+1 flavor QCD

Abstract

We determine the curvature of the (pseudo)critical line of QCD with $n_f$=2+1 staggered fermions at nonzero temperature and quark density, by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed adopting the HISQ/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.\cite{Bazavov:2011nk}, 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 $m_l/m_s=1/20$. In the present investigation we set the chemical potential at the same value for the three quark species, $\hat{I}{¼}_l=\hat{I}{¼}_s\equiv \hat{I}¼$. We explore lattices of different spatial extensions, $16^3\times 6$ and $24^3\times 6$, to check for finite size effects, and present results on a $32^3\times 8$ lattice, to check for finite cut-off effects. We discuss our results for the curvature $\hat{I}º$ of the critical line at $\hat{I}¼=0$, which indicate $\hat{I}º=0.018(4)$, and compare them with previous lattice determinations by alternative methods and with experimental determinations of the freeze-out curve.

6 pages, 4 figures, 1 table