New Results on Hard Probes in Heavy-Ion Collisions with ALICE

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