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

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 blast wave, we perform Bayesian inference of the shear and bulk viscosities of the QGP at hadronization with a temperature of T≈160 MeV by analyzing the φ and Ω data in Au+Au collisions at √sNN=19.6--200 GeV and Pb+Pb collisions at √sNN=2.76 TeV, corresponding to a baryon chemical potential variation from μB≈0 (at √sNN=2.76 TeV) to 200 MeV (at √sNN=19.6 GeV). We find that the shear viscosity to enthalpy ratio ηT/(ε+P) of the QGP at hadronization decreases as μB increases, with ηT/(ε+P)≈0.18 at μB=0 and ηT/(ε+P)≈0.08 at μB=200 MeV, while the corresponding specific bulk viscosity is essentially constant with ζT/(ε+P)=0.02--0.04 for μB<200 MeV. Our results suggest that the QGP at hadronization (T≈160 MeV) with finite baryon density is more close to perfect fluid than that with zero baryon density.