Azimuthal elliptic anisotropy ($v_{_{2}}$) of high-$p_{_{T}}$ direct $\gamma$ in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV

Abstract

Preliminary results from the STAR collaboration for the azimuthal elliptic anisotropy $(v_{_{2}})$ of high transverse momentum ($p_{_{T}}$) direct photons ($\gamma_{_{dir}}$) produced at mid-rapidity ($|\eta^{\gamma_{_{dir}}}|<1$) in Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$~GeV are presented, and compared to the measured $(v_{_{2}})$ of neutral pions ($\pi^{0}$) in the same kinematic range. The electromagnetic transverse shower profile is used to distinguish $\pi^{0}$ from direct photons. The measured $v_{_{2}}^{\gamma_{_{dir}}}(p_{_{T}})$ at high $p_{_{T}}$ ($8< p_{_{T}}^{\gamma_{_{dir}}}<20$~GeV/$c$) is found to be smaller than that of $\pi^{0}$ and consistent with zero when using the forward detectors in determining the event plane.