QGP formation time and the large photon v2 puzzle in heavy ion collisions

TL;DR

This paper explores how the formation time of quark-gluon plasma influences the large photon elliptic flow in heavy ion collisions, proposing a two-time-scale model that aligns with hadron data and suggests a gluon-dominant state.

Contribution

It introduces a two-time-scale framework for understanding photon production and flow, linking thermal and chemical equilibrium times to experimental observations.

Findings

The two-time-scale model explains the photon v2 puzzle.

A gluon-dominant matter state is proposed in heavy ion collisions.

The model aligns photon spectra and flow with hadron data.

Abstract

We investigate the large photon v2 puzzle and the two time scales of thermal and chemical equilibrium in heavy ion collisions. The two-time-scale picture has a weak effect on the transverse moemntum spectrum of direct photons, but a strong effect on the elliptic flow of direct photons. Thus both the spectrum and the elliptic flow of direct photons may be explained with hydro evolution constrained with hadron data. In such a picture, a gluon dominant matter appears in heavy ion collisions. This new matter may impact strongly to other fields such as astrophysics and cosmology.