Scalings of elliptic flow for a fluid at finite shear viscosity

Within a parton cascade approach we investigate the scaling of the differential elliptic flow nu(2)(p(T)) With eccentricity is an element of(x) and system size and its sensitivity to finite shear viscosity. We present calculations for shear viscosity to entropy density ratio eta/s in the range from 1/4 pi up to 1/pi, finding that the nu(2) saturation value varies by about a factor 2. Scaling of nu(2)(p(T))/is an element of(x) is seen also for finite eta/s which indicates that it does not prove a perfect hydrodynamical behavior, but is compatible with a plasma at finite eta/s. Introducing a suitable freeze-out condition. we see a significant reduction of nu(2)(p(T)) especially at intermediate p(T) and for more peripheral collisions. This causes a breaking of the scaling for both nu(2)(p(T)) and the p(T)-averaged nu(2), while keeping the scaling Of nu(2)(p(T))/(nu(2)). This is in better agreement with the experimental observations and shows as a first indication that the ills should be significantly lower than the pQCD estimates. We finally point out the necessity to include the hadronization via coalescence for a definite evaluation of eta/s front intermediate p(T) data. (C) 2008 Elsevier B.V. All rights reserved.