  We study the gluon radiation spectrum off a hard in-medium produced quark in
the multiple soft rescattering formalism of
Baier-Dokshitzer-Mueller-Peigne-Schiff, and of Zakharov (BDMPS-Z). Its
dependence on the quark and gluon energy, on the gluon transverse momentum, on
the in-medium pathlength and on the rescattering properties of the nuclear
medium is analyzed quantitatively. The two components of gluon radiation, the
hard vacuum radiation associated to the quark production vertex, and the
medium-induced rescattering contribution interfer destructively. For small
spatial extensions of the medium, this destructive interference overcompensates
the hard vacuum radiation, and the total medium-induced radiative energy loss
decreases proportional to L^3. Medium-induced gluon production dominates only
above a finite critical length which varies between 3 and more than 6 fm
depending on the rescattering properties of the medium. Deviations from the
BDMPS-L^2-behaviour persist above the critical length. The medium dependence of
the angular gluon distribution is dominated by Brownian transverse momentum
broadening. This results in a depletion of the low transverse momentum part of
both the hard and the medium-induced contribution. As a consequence, the
medium-induced energy loss outside a finite angular cone size can be more than
a factor two larger than the total medium-induced radiative energy loss. We
discuss implications of these results for the jet quenching signal in
relativistic heavy ion collisions at RHIC and LHC.

High Energy Physics - Phenomenology