Suppression of forward dilepton production from an anisotropic quark-gluon plasma

TL;DR

This paper models the rapidity-dependent dilepton yields from an anisotropic quark-gluon plasma, showing potential suppression at LHC energies that could help determine the plasma's isotropization time.

Contribution

It introduces a phenomenological model that interpolates between early anisotropic and late isotropic plasma expansion, linking dilepton suppression to plasma thermalization.

Findings

Forward dilepton production is suppressed by up to a factor of 3 at LHC energies.

Suppression depends on the assumed isotropization time of 2 fm/c.

Model suggests dilepton yields can probe plasma isotropization timing.

Abstract

We calculate the rapidity dependence of leading-order medium dilepton yields resulting from a quark-gluon plasma which has a local time-dependent anisotropy in momentum space. We present a phenomenological model which includes temporal evolution of the plasma anisotropy parameter, xi, and the hard momentum scale, p_hard. Our model interpolates between 1+1 dimensional collisionally-broadened expansion at early times and 1+1 dimensional ideal hydrodynamic expansion at late times. Using our model, we find that at LHC energies, forward high-energy medium dilepton production would be suppressed by up to a factor of 3 if one assumes an isotropization/thermalization time of 2 fm/c. Therefore, it may be possible to use forward dilepton yields to experimentally determine the time of onset of locally isotropic hydrodynamic expansion of the quark-gluon plasma as produced in ultrarelativistic heavy-ion collisions.