The QGP shear viscosity - elusive goal or just around the corner?

With the new viscous hydrodynamic + hadron cascade hybrid code VISHNU, a rather precise (O(25%)) extraction of the quark gluon plasma (QGP) shear viscosity (eta/s)(QGP) from heavy-ion elliptic flow data is possible if the initial eccentricity of the collision fireball is known with <5% accuracy. At this point, eccentricities from initial state models differ by up to 20%, leading to an O(100%) uncertainty for (eta/s)(QGP). It is shown that a simultaneous comparison of elliptic and triangular flow, upsilon(2) and upsilon(3), puts strong constraints on initial state models and can largely eliminate the present uncertainty in (eta/s)(QGP). The variation of the differential elliptic flow upsilon(2)(p(T)) for identified hadrons between RHIC and LHC energies provides additional tests of the evolution model.