Virtual photon polarization and dilepton anisotropy in relativistic nucleus-nucleus collisions

TL;DR

This paper investigates how virtual photon polarization and dilepton angular anisotropy in relativistic nucleus-nucleus collisions reveal information about the medium's conditions, flow, and phases through hydrodynamic modeling.

Contribution

It introduces a hydrodynamic framework to analyze dilepton anisotropy, considering both QGP and hadronic phases, highlighting the effects of flow, momentum, and invariant mass.

Findings

Dilepton anisotropy depends on flow, momentum, and mass.

Angular anisotropy varies between QGP and hadronic phases.

Hydrodynamic effects influence virtual photon polarization signals.

Abstract

The polarization of virtual photons produced in relativistic nucleus-nucleus collisions provides information on the conditions in the emitting medium. In a hydrodynamic framework, the resulting angular anisotropy of the dilepton final state depends on the flow as well as on the transverse momentum and invariant mass of the photon. We illustrate these effects in dilepton production from quark-antiquark annihilation in the QGP phase and $\pi^+\pi^-$ annihilation in the hadronic phase for a static medium in global equilibrium and for a longitudinally expanding system.