  Hard partons propagating through hot and dense matter lose energy, leading to
the observed depletion of hard hadron spectra in nucleus nucleus collision as
compared to scaled proton proton collisions. This lost energy has to be
redistributed in the medium due to the conservation of energy, which is
manifest in the p_T dependence of the angular correlation pattern of hadrons
associate with a (semi-) hard trigger. While at low p_T a splitting of a broad
peak is observed, at high p_T the structure shows vacuum width, albeit with
reduced yield. This sugests a transfer of energy from hard partons to a
collectively recoiling medium. We present a systematic study of these phenomena
using a realistic medium evolution and a Monte-Carlo simulation of the
experimental trigger and show what information about the medium can be derived
from multiparticle correlations.
