On angular ordering in medium-induced radiation

Abstract

Medium-induced gluon radiation gives rise to the strong energy loss observed in single hadron spectra in heavy ion collisions. Its angular structure, leading e.g. to intra-jet correlations, is only known for the one-gluon inclusive case. In the vacuum, properties such as angular ordering appear when considering less inclusive distributions due to destructive interference effects. We present a calculation which takes into account interference effects in a medium for a setup in which we consider gluon radiation off a quark-antiquark pair with a given opening angle. Surprisingly, computing the spectrum at leading-log accuracy we find that an ordering exists which is exactly opposite from that in the vacuum. We estimate the magnitude of the effect along with a discussion of the implications of such “anti-angular ordering” on jet physics in heavy ion collisions.