Abstract
Charged-particle spectra associated with direct photon (γ dir) and π0 are measured in p+p and Au+Au collisions at center-of-mass energy √sNN=200 GeV with the STAR detector at the Relativistic Heavy Ion Collider. A shower-shape analysis is used to partially discriminate between γdir and π0. Assuming no associated charged particles in the γdir direction (near side) and small contribution from fragmentation photons (γfrag), the associated charged-particle yields opposite to γdir (away side) are extracted. In central Au+Au collisions, the charged-particle yields at midrapidity (|η|dir and π0 (ηdir and π0 and independent of the γdir energy within uncertainties. These measurements indicate that, in the kinematic range covered and within our current experimental uncertainties, the parton energy loss shows no sensitivity to the parton initial energy, path length, or color charge.