Study of jet properties in lead-lead collisions at $\sqrt{s_{NN}}$=2.76$ TeV using the ATLAS detector at LHC

The centrality dependence has been determined for charged particles and for single jets of different jet sizes in lead-lead collisions in ATLAS at a per-nucleon center of mass energy of 2.76 TeV. In a sample of lead-lead collisions corresponding to an integrated luminosity of ~7 mub−1, jets are reconstructed calorimetrically using the anti-kt algorithm with varying radius parameter values. The underlying event, including elliptic flow modulations, is measured and subtracted event-by-event, yielding measurements of jet energies above the ambient background. The lead-lead collision centrality is characterized using the per-event total transverse energy measured in the ATLAS forward calorimeters which cover the pseudorapidity range 3.2-4.9 for both positive and negative pseudorapidities. The number of nucleon-nucleon collisions, Ncoll, corresponding to the chosen centrality bins, is estimated using standard Glauber Monte Carlo methods. The centrality dependence of the jet yield is characterized by the jet R_cp, the ratio of the jet per-event yields divided by Ncoll in a given centrality bin to the same quantity in a peripheral centrality bin. Using this measure, jet production at transverse momenta, pT > 60 GeV is found to be suppressed by more than a factor of two in the 10% most central collisions. The single jet results complement measurements of the dijet asymmetry and the observed suppression of charged particle spectra, and can be compared to the behavior of other hard probes.