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

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.