  Jets physics in heavy ion reactions is an important new area of active
research at the Relativistic Heavy Ion Collider (RHIC) and at the Large Hadron
Collider (LHC) that paves the way for novel tests of QCD multi-parton dynamics
in dense nuclear matter. At present, perturbative QCD calculations of hard
probes in elementary nucleon-nucleon reactions can be consistently combined
with the effects of the nuclear medium up to $ {\cal O}(\alpha_s^3) $. While
such accuracy is desirable but not necessary for leading particle tomography,
it is absolutely essential for the new jet observables. With this motivation,
we present first results and predictions to $ {\cal O}(\alpha_s^3) $ for the
recent LHC lead-lead (Pb+Pb) run at a center-of-mass energy of 2.76 TeV per
nucleon-nucleon pair. Specifically, we focus on the suppression of the single
and double inclusive jet cross sections. Our analysis includes not only
final-state inelastic parton interactions in the QGP, but also initial-state
cold nuclear matter effects and an estimate of the non-perturbative
hadronization corrections. We demonstrate how an enhanced di-jet asymmetry in
central Pb+Pb reactions at the LHC, recently measured by the ATLAS and CMS
experiments, can be derived from these results. We show quantitatively that a
fraction of this enhancement may be related to the ambiguity in the separation
between the jet and the soft background medium and/or the diffusion of the
parton shower energy away from the jet axis through collisional processes. We
point to a suite of measurements that can help build a consistent picture of
parton shower modification in heavy ion collisions at the LHC.
