The shear viscosity to entropy ratio ($\eta /s$) is estimated for the hot and dense QCD matter created in $\mathrm{Au}+\mathrm{Au}$ collisions at BNL Relativistic Heavy Ion Collider ($\sqrt{s_{NN}}=200\mathrm{GeV}$). A very low value is found; $\eta /s\sim 0.1$, which is close to the conjectured lower bound ($1/4\pi$). It is argued that such a low value is indicative of thermodynamic trajectories for the decaying matter which lie close to the QCD critical end point.

• Received 26 September 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.092301