Angular dependence of the radiative gluon spectrum and the energy loss of hard jets in QCD media

The induced momentum spectrum of soft gluons radiated from a high energy quark propagating through a QCD medium is derived in the Baier-Dokshitzer-Mueller-Peigné-Schiff 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 behavior in terms of the variable ${\theta }_{\mathrm{cone}}^2{L}^3\mathrm{q̂}$ where L is the size of the medium and $\mathrm{q̂}$ the transport coefficient. Phenomenological implications for the differences between cold and hot QCD matter are discussed.