Dilepton production from a viscous QGP

This work calculates the first correction to the leading order dilepton production rates due to shear viscosity in an expanding gas. The modified rates are integrated over the space–time history of a viscous hydrodynamic simulation of RHIC collisions. The net result is a hardening of q⊥ spectrum with the magnitude of the correction increasing with invariant mass. We argue that a thermal description is reliable for invariant masses less than . For reasonable values of the shear viscosity and thermalization time Mmax≈4.5 GeV. Finally, the early emission from a viscous medium is compared to emission from a longitudinally free streaming plasma. Qualitative differences in q⊥ spectrum are seen which could be used to extract information on the thermalization time, viscosity to entropy ratio and possibly the thermalization mechanism in heavy-ion collisions.