Photons from anisotropic Quark-Gluon-Plasma

TL;DR

This paper investigates how the anisotropic expansion of quark-gluon plasma in heavy ion collisions affects photon production, revealing significant dependencies on isotropization time and initial conditions, with potential enhancement factors.

Contribution

It introduces a phenomenological model to study the impact of time-dependent momentum-space anisotropy on photon yields in QGP, highlighting the importance of early-time anisotropy effects.

Findings

Photon yield depends strongly on isotropization time.

Early anisotropy can enhance photon production by up to a factor of 10.

Enforcing fixed final multiplicity reduces the enhancement effect.

Abstract

We calculate medium photons due to Compton and annihilation processes in an anisotropic media. The effects of time-dependent momentum-space anisotropy of {\em Quark-Gluon-Plasma} (QGP) on the medium photon production are discussed. Such an anisotropy can results from the initial rapid longitudinal expansion of the matter, created in relativistic heavy ion collisions. A phenomenological model for the time-dependence of the parton hard momentum scale, $p_{hard}(\tau)$, and anisotropy parameter, $\xi(\tau)$, has been used to describe the plasma space-time evolution. We find significant dependency of photon yield on the isotropization time ($\tau_{iso}$). It is shown that the introduction of early time momentum-space anisotropy can enhance the photon production by a factor of $10 (1.5)$ (in the central rapidity region) for {\em free streaming} ({\em collisionally-broadened}) {\em interpolating} model if we assume fixed initial condition. On the other hand, enforcing the fixed final multiplicity significantly reduces the enhancement of medium photon production.