Baryon density dependence of viscosities of the quark-gluon plasma at hadronization

Abstract

The $ϕ$ meson and $Ω$ baryon provide unique probes of the properties of the quark-gluon plasma (QGP) at hadronization in relativistic heavy-ion collisions. Using the quark recombination model with the quark phase-space information parameterized in a viscous blastwave, we perform Bayesian inference of the shear and bulk viscosities of the QGP at hadronization with a temperature of $T\sim 160$ MeV by analyzing the $ϕ$ and $Ω$ data in Au+Au collisions at $\sqrt{s_{\rm NN}}=$ 19.6-200 GeV and Pb+Pb collisions at $\sqrt{s_{\rm NN}}=$ 2.76 TeV, corresponding to a baryon chemical potential variation from $μ_B\approx 0$ (at $\sqrt{s_{\rm NN}}= 2.76$ TeV) to $200$ MeV (at $\sqrt{s_{\rm NN}}= 19.6$ GeV). We find that the shear viscosity to enthalpy ratio $ηT/(ε+P)$ of the QGP at hadronization decreases as $μ_B$ increases, with $ηT/(ε+P)\approx 0.18$ at $μ_B=0$ and $ηT/(ε+P)\approx 0.08$ at $μ_B=200$ MeV, while the corresponding specific bulk viscosity is essentially constant with $ζT/(ε+ P)=0.02\sim 0.04$ for $μ_B<200$ MeV. Our results suggest that the QGP at hadronization ($T\sim 160$ MeV) with finite baryon density is more close to perfect fluid than that with zero baryon density.

9 pages, 3 figures, 2 tables. Some details and discussions added. Accepted version to appear in PRC