Angular Dependence of the Radiative Gluon Spectrum and the Energy Loss of Hard Jets in QCD Media

Abstract

The induced momentum spectrum of soft gluons radiated from a high energy quark propagating through a QCD medium is derived in the BDMPS formalism. A calorimetric measurement for the medium dependent energy lost by a jet with opening angle ${\theta }_{\mathrm{cone}}$ is proposed.The fraction of this energy loss with respect to the integrated one appears to be the relevant observable.It exhibits a universal behaviour in terms of the variable ${\theta }_{\mathrm{cone}}^2{L}^3\hat{q}$ where $L$ is the size of the medium and $\hat{q}$ the transport coefficient. Phenomenological implications for the differences between cold and hot QCD matter are discussed.

Comments: 13 pages and 7 figures, RevTex