Viscosity from elliptic flow: Clearing the path towards precision

Using viscous relativistic hydrodynamics we show that systematic studies of the impact parameter dependence of the eccentricity-scaled elliptic flow v₂/ε can distinguish between different models for the calculation of the initial source eccentricity ε. This removes the largest present uncertainty in the extraction of the specific viscosity of the matter created in relativistic heavy-ion collisions from precise elliptic-flow measurements.