Performance of the ATLAS Tau Trigger system with 7 TeV pp collisions at the LHC

Abstract

The LHC has started operation and provided roughly 60 nb − 1 of 7 TeV proton-proton collisions in the period March–June 2010. These data have been used to understand the performance of the ATLAS experiment, and in particular, of the tau trigger system. The tau trigger is a key element in the discovery of new physics, where tau lepton final states play a crucial role. It allows efficient collection of the physics signal, while keeping the rate of background events within the allowed bandwidth. During 2010 it has been commissioned in various stages. At first, the hardware-based first level trigger (L1) was used to select interesting high p T physics samples. During this period the High Level Trigger (HLT) was running online, but not rejecting any events. This stage has allowed for a detailed study of the HLT performance before activation. At a later time, when the luminosity was high enough that the rejection offered by the L1 trigger alone was not sufficient without compromising the collection of interesting physics events, the active selection at the HLT was turned on. This contribution will summarize the status of the tau trigger system at the different stages of data taking, emphasizing the key elements of the online selection and their performance. Methods for obtaining trigger efficiency curves from data will be shown and first results presented. The strategy for ensuring measurements of Standard Model and new physics will be outlined, in light of the recent real data results.