Rapidity distribution of photons from an anisotropic Quark-Gluon-Plasma

TL;DR

This paper investigates how pre-equilibrium momentum-space anisotropy in Quark-Gluon Plasma affects photon rapidity distribution, revealing significant modifications depending on the model parameters and initial conditions.

Contribution

It introduces a phenomenological model to study the impact of anisotropy on photon production in QGP, highlighting the effects of different initial conditions and evolution scenarios.

Findings

Anisotropy significantly modifies photon rapidity distribution.

Free-streaming models show enhancement at fixed initial conditions.

Collisionally-broadened models exhibit suppression beyond certain rapidities.

Abstract

We calculate rapidity distribution of photons due to Compton and annihilation processes from {\em Quark Gluon Plasma} (QGP) with pre-equilibrium momentum-space anisotropy. We also include contributions from hadronic matter with late stage transverse expansion. A phenomenological model has been used for the time evolution of hard momentum scale $p_{\rm hard}(\tau)$ and anisotropy parameter $\xi(\tau)$. As a result of pre-equilibrium momentum-space anisotropy, we find significant modification of photons rapidity distribution. For example, with {\em fixed initial condition} (FIC) {\em free-streaming} ($\delta=2$) interpolating model we observe significant enhancement of photon rapidity distribution at fixed $p_T$, where as for FIC {\em collisionally-broadened} ($\delta=2/3$) interpolating model the yield increases till $y \sim 1$. Beyond that suppression is observed. With {\em fixed final multiplicity} (FFM) {\em free-streaming} interpolating model we predict enhancement of photon yield which is less than the case of FIC. Suppression is always observed for FFM {\em collisionally-broadened} interpolating model.