Measuring Quark-Gluon-Plasma Thermalization Time with Dileptons

TL;DR

This paper proposes a method to determine the thermalization time of quark-gluon plasma by analyzing dilepton yields, which are sensitive to plasma anisotropy and isotropization time.

Contribution

It introduces a phenomenological model linking dilepton production to plasma anisotropy, enabling experimental estimation of the plasma's thermalization time.

Findings

High-energy dilepton yields depend on isotropization time.

Dilepton measurements can reveal early-time plasma anisotropies.

Model interpolates between free streaming and hydrodynamic behavior.

Abstract

We calculate the medium dilepton yield from a quark-gluon plasma which has a time-dependent local momentum-space anisotropy. A phenomenological model for the hard momentum scale, p_hard(tau), and plasma anisotropy parameter, xi(tau), is constructed which interpolates between free streaming behavior at early times (tau << tau_iso) and ideal hydrodynamic behavior at late times (tau >> tau_iso). We show that high-energy dilepton production is sensitive to the assumed plasma isotropization time, tau_iso, and can therefore be used to experimentally determine the time of onset for hydrodynamic expansion of a quark-gluon plasma and the magnitude of expected early-time momentum-space anisotropies.