Estimation of isotropization time ($\tau_{\rm iso}$) of QGP from direct photons

TL;DR

This paper estimates the isotropization time of quark-gluon plasma by analyzing direct photon spectra, demonstrating that initial momentum anisotropy improves data agreement and providing a range for $ au_{iso}$ between 0.5 and 1.5 fm/c.

Contribution

It introduces a method to extract the QGP isotropization time using photon spectra considering initial anisotropy, improving upon isotropic models.

Findings

Anisotropic models fit photon data better than isotropic ones.

Estimated isotropization time range is 0.5 to 1.5 fm/c.

Initial anisotropy significantly affects photon yield predictions.

Abstract

We calculate transverse momentum distribution of direct photons from various sources by taking into account the initial state momentum anisotropy of quark gluon plasma (QGP). The total photon yield is then compared with the recent measurement of photon transverse momentum distribution by the PHENIX collaboration. It is also demonstrated that the presence of such an anisotropy can describe the PHENIX photon data better than the isotropic case in the present model. We show that the isotropization time thus extracted lies within the range $1.5 \geq\tau_{\rm iso} \geq 0.5$ fm/c for the initial condition used here.