Anisotropies in momentum space at finite shear viscosity in ultrarelativistic heavy-ion collisions

Within a parton cascade we investigate the dependence of aniscitropies in momentum space, namely the elliptic flow nu(2) = < cos(2 phi)> and the nu(4) = < cos(4 phi)>, on both the finite shear viscosity eta and the freeze-out (f.o.) dynamics at the RHIC energy of 200 GeV. In particular the impact of the f.o. dynamics is discussed looking at two different procedures: switching-off the collisions when the energy density goes below a fixed value or reducing the cross section according to the increase in eta/s from a QGP phase to a hadronic one. We address the relation between the scaling Of nu(2)(p(T)) with the eccentricity epsilon(x) and with the integrated elliptic flow. We show that the breaking of the nu(2)(p(T))/epsilon(x) Scaling is not coming mainly from the finite eta/s but from the f.o. dynamics and that the nu(2)(p(T)) is weakly dependent on the f.o. scheme. On the other hand the nu(2)(p(T)) is found to be much more sensitive to both the eta/s and the f.o. dynamics and hence is indicated to put better constraintson the properties of the QGP. A first semi-quantitative analysis shows that both nu(2) and nu(2) (with the smooth f.o.) consistently indicate a plasma with 4 pi eta/s similar to 1 - 2. (C) 2009 Elsevier B.V. All rights reserved.