  Hard probes - final state particles related to an interaction with large
momentum transfer or mass scale - play a distinguished role in the discovery
and the study of the Quark-Gluon Plasma (QGP), a phase of deconfined quarks and
gluons reached at high temperatures in heavy ion collisions. In heavy ion
collisions, parton scatterings with a large momentum transfer ($1/Q \ll 1$
fm/$c$) occur prior to QGP formation and thus provide a source of coloured
probe particles for the QGP created in the later stage of the reaction. The
hard scattered partons and the subsequent parton shower interact strongly with
the QGP and its constituents via elastic and radiative processes before
hadronization into jets of observable particles. Thus, the comparison to jet
and high-$p_T$ observables in pp (vacuum) potentially probes their modification
due to medium effects. One of the key observables in the discovery and
investigation of these jet modifications has been the nuclear modification
factor $R_{AA}$, for which new results on charged particle production in
different colliding systems are presented and the question of apparant
suppression in peripheral Pb-Pb collisions is addressed. Fore more differential
studies of the jet sub-structure and hence the parton shower evolution in the
medium, recent results on jet grooming in heavy ion colisions are presented.
