High-$p_{{}_T}$ Direct Photon Azimuthal Correlation Measurements

Abstract

The azimuthal correlations of direct photons (${\gamma }_{{}_{dir}}$) with high transverse momentum ($p_{{}_T}$), produced at mid-rapidity ($|{\eta }^{{\gamma }_{{}_{dir}}}|<1$) in Au+Au collisions at center-of-mass energy $\sqrt{s_{{}_{NN}}}=200$~GeV, are measured and compared to those of neutral pions (${\pi }^0$) in the same kinematic range. The measured azimuthal elliptic anisotropy of direct photon, $v_{{}_2}^{{\gamma }_{{}_{dir}}}(p_{{}_T})$, 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 ($2.4<|\eta |<4.0$) in reconstructing the event plane. The associated charged hadron spectra recoiled from ${\gamma }_{{}_{dir}}$ show more suppression than those recoiled from ${\pi }^0$ $(I_{AA}^{{\gamma }_{{}_{dir}}-h^{\pm }}<I_{AA}^{{\pi }^0-h^{\pm }})$ in the new measured kinematic range $12<p_{{}_T}^{{\gamma }_{{}_{dir}},{\pi }^0}<24$~GeV/$c$ and $3<p_{{}_T}^{assoc}<24$~GeV/$c$.

arXiv commentXXIV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions. arXiv admin note: text overlap with arXiv:1408.0576

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