The Tau Trigger at the Atlas Experiment

The tau trigger system is a component of the Atlas trigger system. Its purpose is to select events of interest containing hadronically decaying taus, which are signatures for discovery physics events such as Higgs decays, while rejecting background events such as those due to QCD jets. It is composed of three levels, the lowest being hardware based and the higher levels software based. The tau trigger uses cuts on calorimeter and tracking information to determine trigger activation, the stringency of which cuts vary with luminosity. Tau trigger efficiency will be measured through several methods including using the QCD tau fake rate, a tag and probe analysis with Z boson decays, and semi-leptonically decaying ttbar events triggered by a 4-jet trigger.