Extracting the shear viscosity of the quark-gluon plasma from flow in ultra-central heavy-ion collisions

We propose a method for extracting the shear viscosity over entropy density ratio (η/s) of the quark-gluon plasma from experimental data. We argue that uncertainty due to poor knowledge of the earliest stages of a heavy-ion collision is smallest for ultra-central events. The most precise value of η/s can thus be obtained from a global fit to pT-integrated Fourier harmonics of azimuthal correlations. We further outline a method for quantifying the overall uncertainty in the extracted value. Only after a comprehensive and systematic accounting of all sources of uncertainty can a reliable measurement be claimed. In these proceedings we report preliminary results; full and final results will be presented in a separate publication.