The isentropic equation of state of 2-flavor QCD

TL;DR

This study calculates the isentropic equation of state for 2-flavor QCD using Taylor expansions, providing insights into dense matter behavior relevant for heavy ion collisions across different temperature regimes.

Contribution

It introduces higher-order expansion coefficients for energy and entropy densities in 2-flavor QCD and analyzes lines of constant entropy per baryon in various temperature regimes.

Findings

Lines of constant S/N_B are well approximated by constant μ_q/T at high T.

In the low T phase, μ_q increases as T decreases, aligning with resonance gas models.

The ratio p/ε and the softest point show minimal dependence on S/N_B.

Abstract

Using Taylor expansions of the pressure obtained previously in studies of 2-flavor QCD at non-zero chemical potential we calculate expansion coefficients for the energy and entropy densities up to ${\cal O}(\mu_q^6)$ in the quark chemical potential. We use these series in $\mu_q/T$ to determine lines of constant entropy per baryon number ($S/N_B$) that characterize the expansion of dense matter created in heavy ion collisions. In the high temperature regime these lines are found to be well approximated by lines of constant $\mu_q/T$. In the low temperature phase, however, the quark chemical potential is found to increase with decreasing temperature. This is in accordance with resonance gas model calculations. Along the lines of constant $S/N_B$ we calculate the energy density and pressure. Within the accuracy of our present analysis we find that the ratio $p/\epsilon$ for $T>T_0$ as well as the softest point of the equation of state, $(p/\epsilon)_{min}\simeq 0.075$, show no significant dependence on $S/N_B$.