Heavy Ion Physics with the ATLAS Detector at the LHC

First results on jet, $Jpsi$ and $Z$ production are presented from the first lead-lead run at the LHC, using the ATLAS detector. The transverse energies of dijets in opposite hemispheres is observed to become systematically more unbalanced with increasing event centrality, leading to a large number of events which contain highly asymmetric dijets. This was the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium. Also, using the ATLAS muon spectrometer, a centrality-dependent suppression has been observed in the yield of $J/psi$ mesons. It is found to be qualitatively similar to the trends observed at previous, lower energy experiments. The relative yields of $Z$ bosons as a function of centrality are also presented, although the low statistics precludes any strong conclusions. These results provide a first look at the modification of high $p_T$ processes in heavy ion collisions at the highest-available beam energy.