The QCD phase diagram from analytic continuation

TL;DR

This paper uses lattice QCD simulations with analytic continuation from imaginary to real chemical potential to map the QCD phase diagram, accurately determining the curvature of the transition line with controlled systematic errors.

Contribution

It introduces a method to determine the QCD transition line at small chemical potentials via analytic continuation, with consistent results across multiple observables and systematic error control.

Findings

The transition line curvature is $oxed{ ext{0.0149} ext{ with } ext{error} ext{ of } ext{0.0021}}$.

Systematic errors are controlled up to $oxed{ ext{300 MeV}}$ in baryon chemical potential.

Consistent results obtained from three different observables.

Abstract

We present the crossover line between the quark gluon plasma and the hadron gas phases for small real chemical potentials. First we determine the effect of imaginary values of the chemical potential on the transition temperature using lattice QCD simulations. Then we use various formulas to perform an analytic continuation to real values of the baryo-chemical potential. Our data set maintains strangeness neutrality to match the conditions of heavy ion physics. The systematic errors are under control up to $\mu_B\approx 300$ MeV. For the curvature of the transition line we find that there is an approximate agreement between values from three different observables: the chiral susceptibility, chiral condensate and strange quark susceptibility. The continuum extrapolation is based on $N_t=$ 10, 12 and 16 lattices. By combining the analysis for these three observables we find, for the curvature, the value $\kappa = 0.0149 \pm 0.0021$.