A fast hardware tracker for the ATLAS trigger system (original) (raw)

Selecting interesting events online is a very challenging task in LHC experiments. By the end of 2014, the LHC will run with an energy of 13 or 14 TeV and instantaneous luminosities which could exceed 10 34 interactions per cm 2 and per second. The triggering in the ATLAS detector is realized using a three level trigger approach, in which the first level is hardware based and the second and third stage are realized using large computing farms. It is a crucial and non-trivial task for triggering to maintain a high efficiency for events of interest while suppressing effectively the very high rates of inclusive QCD processes, which constitute mainly background. At the same time the trigger system has to be robust and provide sufficient operational margins to adapt to changes in the running environment. In the current design track reconstruction can be performed only in limited regions of interest at second stage trigger and the CPU requirements may limit this even further at the highest instantaneous luminosities. Providing high quality track reconstruction over the entire detector volume for the second stage trigger decision would allow gains in efficiency and background rejection for triggers on tau leptons, b-hadrons and help reduce the luminosity dependence of isolation requirements for electrons and muons. The Fast Track Trigger (FTK) is an ongoing upgrade project aimed at providing track reconstruction using the silicon microstrip and pixel detectors. Pattern recognition and track fitting are executed in a hardware system utilizing massive parallel processing and achieve a tracking performance close to that of the global track reconstruction. The FTK systems design, based on a mixture of advanced technologies and expected physics performance will be presented.