Gamma-Jet Tomography of Quark-Gluon Plasma in High-Energy Nuclear Collisions

Within the next-to-leading order (NLO) perturbative QCD (pQCD) parton model, suppression of away-side hadron spectra associated with a high pT photon due to parton energy loss is shown to provide a complete tomographic picture of the dense matter formed in high-energy heavy-ion collisions at RHIC. Dictated by the shape of the γ-triggered jet spectrum in NLO pQCD, hadron spectra at large are more susceptible to parton energy loss and therefore are dominated by surface emission of γ-triggered jets, whereas small zT hadrons mainly come from fragmentation of jets with reduced energy from volume emission. These lead to different centrality dependence of the hadron suppression in different regions of zT.