Knudsen number, ideal hydrodynamic limit for elliptic flow, and QGP viscosity in √(sNN)=62 and 200 GeV Cu+Cu/Au+Au collisions

Taking into account entropy generation during evolution of a viscous fluid, we have estimated the inverse Knudsen number, the ideal hydrodynamic limit for elliptic flow, and the quark-gluon plasma viscosity to entropy ratio in √(sNN)=62 and 200 GeV Cu+Cu/Au+Au collisions. The viscosity to entropy ratio is estimated as η/s=0.17±0.10±0.20, where the first error is statistical, the second one is systematic. In a central Au+Au collision, the inverse Knudsen number is ≅2.80±1.63, which is presumably too small for complete equilibration. In peripheral collisions it is even less. The ideal hydrodynamic limit for elliptic flow is ∼40% more than the experimental flow in a central collision.