Back-to-back pair suppression at large transverse momentum in Au + Au collisions at PHENIX

Suppression of jet fragments due to parton energy loss is a well known phenomena from high pT measurements of single particles (RAA) and back-to-back pairs (IAA) in central and mid-central heavy ion collisions. However the nature of the parton-medium interaction is still not well-understood and an outstanding issue to be fully resolved is the characterization of the path-length dependence of energy loss. A recent study of pair correlations between large transverse momentum neutral pion triggers () and charged hadron partners () in mid-central (20-60%) Au+Au collisions as a function of trigger orientation with respect to the reaction plane is discussed. The dependence found in the suppression of (di-)jet pairs is qualitatively consistent with a picture of little near-side parton energy loss either due to surface bias or fluctuations and increased away-side parton energy loss due to a long path through the medium.