High-energy dileptons from an anisotropic quark-gluon plasma

TL;DR

This paper models dilepton production from an anisotropic quark-gluon plasma, showing that early-stage anisotropies can significantly enhance high-energy dilepton yields, which could help determine plasma isotropization times experimentally.

Contribution

It introduces a phenomenological model for the time evolution of anisotropy and energy scale in a quark-gluon plasma, linking early anisotropic stages to dilepton production.

Findings

High-energy dilepton yield increases by up to 50% due to pre-equilibrium emission.

The model connects dilepton enhancement to plasma isotropization time.

Sufficiently precise data could measure the plasma's isotropization time.

Abstract

We calculate leading-order dilepton yields from a quark-gluon plasma which has a time-dependent anisotropy in momentum space. Such anisotropies can arise during the earliest stages of quark-gluon plasma evolution due to the rapid longitudinal expansion of the created matter. A phenomenological model for the proper time dependence of the parton hard momentum scale, p_hard, and the plasma anisotropy parameter, xi, is proposed. The model describes the transition of the plasma from a 0+1 dimensional collisionally-broadened expansion at early times to a 0+1 dimensional ideal hydrodynamic expansion at late times. We find that high-energy dilepton production is enhanced by pre-equilibrium emission up to 50% at LHC energies, if one assumes an isotropization/thermalization time of 2 fm/c. Given sufficiently precise experimental data this enhancement could be used to determine the plasma isotropization time experimentally.