Roberge-Weiss endpoint at the physical point of $N_f=2+1$ QCD

Abstract

We study the phase diagram of $N_f=2+1$ QCD in the $T-{\mu }_B$ plane and investigate the critical point corresponding to the onset of the Roberge-Weiss transition, which is found for imaginary values of ${\mu }_B$. We make use of stout improved staggered fermions and of the tree level Symanzik gauge action, and explore four different sets of lattice spacings, corresponding to $N_t=4,6,8,10$, and different spatial sizes, in order to assess the universality class of the critical point. The continuum extrapolated value of the endpoint temperature is found to be $T_{\mathrm{RW}}=208(5)$ MeV, i.e. $T_{\mathrm{RW}}/T_c\sim 1.34(7)$, where $T_c$ is the chiral pseudocritical temperature at zero chemical potential, while our finite size scaling analysis, performed on $N_t=4$ and $N_t=6$ lattices, provides evidence for a critical point in the $3d$ Ising universality class.

Comments: 10 pages, 14 eps figures, 2 tables, final version published in Physical Review D