Knudsen number, ideal hydrodynamic limit for elliptic flow, and QGP viscosityin S_(NN)~(1/2) = 62 and 200 GeV Cu+Cu/Au+Au collisions

摘要

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 S_(NN)~(1/2) = 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.