Building a testable shear viscosity across the QCD phase diagram

Abstract

Current experiments at the Relativistic Heavy Ion Collider (RHIC) are probing finite baryon densities where the shear viscosity to enthalpy ratio $\hat{I}\cdot T/w$ of the Quark Gluon Plasma remains unknown. We use the Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $\hat{I}\cdot T/w$ at low temperatures and at finite baryon densities $\ddot{I}{}_B$. We then match $\hat{I}\cdot T/w$ to a QCD-based shear viscosity calculation within the deconfined phase to create a table across $\left\{T,\hat{I}{¼}_B\right\}$ for different cross-over and critical point scenarios at a specified location. We find that these new $\hat{I}\cdot T/w(T,\hat{I}{¼}_B)$ values would require initial conditions at significantly larger $\ddot{I}{}_B$, compared to ideal hydrodynamic trajectories, in order to reach the same freeze-out point.