Anisotropic flow of thermal photons as a quark-gluon plasma viscometer

Understand

We present state-of-the-art calculations of viscous photon emission from nuclear collisions at RHIC and LHC.

• Fluctuating initial density profiles are evolved with event-by-event viscous hydrodynamics.
• Momentum spectra of thermal photons radiated by these explosively expanding fireballs and their $p_T$-differential anisotropic flow coefficients $v_n(p_T)$ are computed, both with and without accounting for viscous corrections to the standard thermal emission rates.
• Viscous corrections to the rates are found to have a larger effect on the $v_n$ coefficients than the viscous suppression of hydrodynamic flow anisotropies.