Formation Time of QGP from Thermal Photon Elliptic Flow

TL;DR

This paper demonstrates that the elliptic flow of thermal photons is highly sensitive to the initial formation time of the QGP, providing a potential method to estimate QGP formation time in heavy-ion collisions.

Contribution

It introduces the sensitivity of thermal photon elliptic flow to the QGP formation time and highlights its potential as a probe for early-stage QGP properties.

Findings

Smaller formation time increases thermal photon yield.

Photon elliptic flow decreases with smaller formation time at high pT.

Hadron elliptic flow is less affected by formation time.

Abstract

We show that the transverse momentum dependent elliptic flow $v_2(p_T)$ of thermal photons is quite sensitive to the initial formation time ($\tau_0$) of Quark Gluon Plasma (QGP) for semi-central collision of gold nuclei at RHIC \cite{tau}. A smaller value of the formation time or a larger initial temperature leads to a significant increase in the thermal photon radiation from QGP phase, which has a smaller $v_2$. The elliptic flow of thermal photon is dominated by the contribution from the quark matter at intermediate and high $p_T$ range and as a result sum $v_2$ decreases with smaller $\tau_0$ for $p_T \ge 1.5$ GeV. On the other hand we find that the elliptic flow parameter for hadrons depends only marginally on the value of $\tau_0$.