  Hard probes in the context of ultrarelativistic heavy ion collisions
represent a key class of observables studied to gain informations about the QCD
medium created in such collisions. However, in practice the so-called jet
tomography has turned out to be more difficult than expected initially. One of
the major obstacles in extracting reliable tomographic information from the
data is that neither the parton-medium interaction nor the medium geometry are
known with great precision, and thus a difference in model assumptions in the
hard perturbative Quantum Choromdynamics (pQCD) modelling can usually be
compensated by a corresponding change of assumptions in the soft bulk medium
sector and vice versa. The only way to overcome this problem is to study the
full systematics of combinations of parton-medium interaction and bulk medium
evolution models. This work presents a meta-analysis summarizing results from a
number of such systematical studies and discusses in detail how certain data
sets provide specific constraints for models. Combining all available
information, only a small group of models exhibiting certain characteristic
features consistent with a pQCD picture of parton-medium interaction is found
to be viable given the data. In this picture, the dominant mechanism is
medium-induced radiation combined with a surprisingly small component of
elastic energy transfer into the medium.
