Exploration of jet energy loss via direct $\gamma$-charged particle azimuthal correlation measurements

Abstract

The multiplicities of charged particles azimuthally associated with direct photons and $\pi^{0}$ have been measured for Au+Au, p+p, and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment. Charged particles with transverse momentum 0.5 $<$ $p_T^{h^{\pm}}$ $<$ 16 GeV/c for p+p and d+Au, and 3 $<$ $p_T^{h^{\pm}}$ $<$ 16 GeV/c for Au+Au and pseudorapidity $\mid\eta\mid$ $\leq$ 1.5 in coincidence with direct photons and $\pi^{0}$ of high transverse momentum 8 $<$ $p_T^{\gamma,\pi^{0}}$ $<$ 16 GeV/c at $\mid\eta\mid$ $\leq$ 0.9 have been used for this analysis. Within the considered range of kinematics, the observed suppressions of the associated yields per direct $\gamma$ in central Au+Au relative to p+p and d+Au are similar and constant with direct photon fractional energy $z_{T}$ ($z_{T}=p_{T}^{h^{\pm}}/p_{T}^{\gamma}$). The measured suppressions of the associated yields with direct $\gamma$ are comparable to those with $\pi^{0}$. The data are compared to theoretical predictions.