The ATLAS jet trigger

The ATLAS jet trigger system has a 3-level structure, and is based on the concept of Region Of Interest, where only regions of the detector around interesting Level-1 objects are reconstructed at the higher levels. This strategy is not well-suited for multi-jet events since it leads to pathologies and efficiency losses. This philosophy has been changed for the jet trigger during 2011, and we now have the possibility of unpacking the full calorimeter at Event Filter. For 2012, full calorimeter unpacking will also be possible (for a small subset of the events) at an intermediate level between Level-1 and Level-2. We also moved to the use of the calibrated jet energy scale at trigger level, and to the application of noise cuts to reduce rate spikes. We will present the performance of the jet trigger in 2011 and from the first runs of 2012.