Tomography of High-Energy Nuclear Collisions with Photon-Hadron Correlations

Within the next-to-leading order (NLO) perturbative QCD (PQCD) parton model, suppression of away-side hadron spectra associated with a high p(T) photon due to parton energy loss is studied in high-energy heavy-ion collisions. Because of the sharp falloff of the gamma-jet spectrum in momentum imbalance p(T)(jet)-p(T)(gamma)> 0 in NLO PQCD, hadron spectra at large z(T)=p(T)(h)/p(T)(gamma)greater than or similar to 1 are more susceptible to parton energy loss and therefore are dominated by surface emission of gamma-associated jets with almost no energy loss, whereas small z(T) hadrons mainly come from the volume emission of jets with reduced energy. These lead to different centrality dependence of the gamma-hadron suppression for different values of z(T). Therefore, a complete measurement of the suppression of gamma-triggered hadron spectra allows a true tomographic study of the quark-gluon plasma in high-energy heavy-ion collisions.