Dilepton to photon ratio, a viscometer of QGP

TL;DR

This paper investigates how the ratio of photon to dilepton emission can serve as a sensitive measure of the viscosity of quark-gluon plasma (QGP) using viscous hydrodynamics.

Contribution

It introduces the photon to dilepton ratio as a novel viscometer for QGP, analyzing viscous effects on dilepton emission within Israel-Stewart hydrodynamics.

Findings

Large invariant mass dileptons are less affected by viscosity.

The photon to dilepton ratio is sensitive to QGP viscosity.

Viscous effects significantly alter dilepton emission patterns.

Abstract

In the Israel-Stewart's 2nd order hydrodynamics, a viscous effect on dilepton emission from a QGP medium is investigated. Dileptons are strongly affected by QGP viscosity. Large invariant mass dileptons, due to their lower velocity, are less affected by viscosity than the low invariant mass dileptons. We also show that the ratio of photon to dilepton is sensitive to the viscosity and can serve as a viscometer for QGP.