Performance of the ATLAS calorimeter trigger in the LHC Run 1 data taking period

Abstract

The ATLAS detector operated very successfully at the LHC Run 1 data taking period collecting a large number of events used for different physics analyses, such as the ones leading to the discovery of the Higgs boson as well as for the search for beyond the Standard Model physics. In the main search channels related to the finding of the Higgs, the ATLAS calorimeter system played a major role by measuring the energy of photons, electrons, jets, taus and neutrinos, via missing transverse energy measurement. The ATLAS trigger system selects from the huge amount of events produced every second, those few that are recorded for physics analyses (less than one out of 40 thousand can be kept). The selection process is performed in three levels with increasing complexity and resolution. The first level is hardware based, seeding the two other software levels called together the HighLevel Trigger (HLT). The paper will describe details of the calorimeter based HLT algorithms with special emphasis on the algorithms used for missing transverse energy reconstruction and jet detection performance which was improved in 2012 with respect to the 2011 data taking despite the higher luminosity levels.