Dilepton production from a viscous QGP

Abstract

This work calculates the first correction to the leading order q\=q 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 Mmax≈(2τ0 T02)/(η/s). 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.