Medium-induced gluon radiation off massive quarks fills the dead cone

We calculate the transverse momentum dependence of the medium-induced gluonenergy distribution radiated off massive quarks in spatially extended QCDmatter. In the absence of a medium, the distribution shows a characteristicmass-dependent depletion of the gluon radiation for angles smaller than m/E,the so-called dead cone effect. Medium-modifications of this spectrum arecalculated as a function of quark mass, initial quark energy, in-mediumpathlength and density. Generically, medium-induced gluon radiation is found tofill the dead cone, but it is reduced at large gluon energies compared to theradiation off light quarks. We quantify the resulting mass-dependence formomentum-averaged quantities (gluon energy distribution and average partonenergy loss), compare it to simple approximation schemes and discuss itsobservable consequences for nucleus-nucleus collisions at RHIC and LHC. Inparticular, our analysis does not favor the complete disappearance of energyloss effects from leading open charm spectra at RHIC.Comment: 27 pages LaTeX, 15 eps-figure