High p_T Direct Photon-Hadron Correlations Using the PHENIX Detector

TL;DR

This paper presents measurements of direct photon-hadron correlations in p+p and Au+Au collisions at 200 GeV, using a statistical background subtraction method, to study jet quenching and medium effects in heavy-ion collisions.

Contribution

It introduces a novel statistical method for subtracting decay photon backgrounds in direct photon-hadron correlation measurements.

Findings

Photon-hadron correlations in p+p serve as a baseline for jet fragmentation.

Au+Au collisions show modifications indicative of medium-induced energy loss.

Results help constrain models of jet quenching and medium response.

Abstract

Jet tomography, the study of differential energy loss of hard scattered partons to infer the density profile of the medium, is greatly improved by precise knowledge of the initial energy of the hard probe. As photons are not strongly interacting, the momentum of the recoil jet from a direct photon trigger is balanced, to a good approximation, by the momentum of the photon. The energy loss of the away-side jet may be viewed as an effective modification of the fragmentation function. Direct photon-hadron correlations in A+A collisions should be sensitive to modified jet fragmentation as well as to medium response effects. Complementary measurements from p+p collisions are necessary to benchmark jet fragmentation expectations at \sqrt{s_NN} = 200 GeV as well as to constrain perturbative calculations in the \gamma+jet channel. Here we present new results from p+p and Au+Au collisions which use a statistical method to subtract the background from decay photons.