The QCD equation of state to $\mathcal{O}(\mu_B^4)$

Abstract

We present results from an ongoing calculation of the QCD equation of state at finite baryon chemical potential $\mu_B$. We use the method of Taylor expansions to circumvent the sign problem and calculate the expansion coefficients to sixth order using HISQ fermions. We work at two lattice spacings, namely $N_\tau=6$ and 8 and, though we do not take the continuum limit, demonstrate that cutoff effects remain under control. We also use our results to construct an equation of state along the freeze-out curve. Using our sixth-order results as a cross-check, we demonstrate that our fourth-order equation of state is suitable for the modeling of dense matter created in heavy ion collisions with center-of-mass energies down to $s_{NN}^{1/2}\sim20$ GeV.