ly Triggering on hadronic Tau Decays in ATLAS : 1 Algorithms and Performance

Hadronic tau decays play a crucial role in Standard Model measurements as well 6 as in the search for physics beyond the Standard Model by the ATLAS experiment at the Large 7 Hadron Collider (LHC). However, hadronic tau decays are difficult to identify and trigger on due 8 to their resemblance to QCD jets. Given the large production cross section of QCD processes, 9 designing and operating a trigger system with the capability to efficiently select hadronic tau 10 decays, while maintaining the rate within the bandwidth limits, is a challenge. This contribution 11 summarizes the algorithms and performance of the ATLAS tau trigger system during the 2011 12 data taking period. The use of resources and implementation of trigger algorithms in the ATLAS 13 trigger architecture is shown in detail. Moreover, comparisons of data and simulation results, 14 studies of the correlation of the variable definitions at different trigger stages as well as efficiency 15 versus rate analyses are the key elements to describe the performance of the tau trigger. Finally, 16 in light of the vast statistics collected in 2011, future prospects for triggering on hadronic tau 17 decays in the 2012 data taking of increased instantaneous luminosity are presented. 18