Direct-photon+hadron correlations to study parton energy loss with the STAR experiment

Abstract

We report new results of $\gamma_{dir}$+hadron and $\pi^{0}$+hadron azimuthal correlations as a measure of the away-side jet-like correlated yields in central Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment from years 2011 and 2009 of data taking, respectively. The charged-hadron per-trigger yields at mid-rapidity $(|\eta| < 1)$ and for transverse momenta $p_{T}^{assoc} > 1.2$ ~GeV/$c$ associated with $\gamma_{dir}$~ and $\pi^{0}$~(for triggers $|\eta| < $0.9, 12 $< p_{T}^{trig} <$ 20 GeV/$c$) in central Au+Au collisions are compared with p+p collisions. The $z_{T}$ ($= \frac{p_{T}^{assoc}}{p_{T}^{trig}}$) dependence, now extending down to $z_{T}$=0.1, of the suppression of the away-side associated yields is presented. We observed that the suppression of away-side associated yields tends to vanish at lower \zT. The dependence of the suppression on both $p_{T}^{assoc}$ and $p_{T}^{trig}$ is also discussed. Finally, these results are compared with various model predictions.