Electron/photon Identification and Standard Model Higgs Process Studies at the High Level Trigger for the ATLAS experiment

The ATLAS experiment, one of the four detectors at the Large Hadron Collider currently under construction at CERN with start–up date in 2007, will search for Standard Model Higgs Bosons and for new physics beyond the Standard Model up to the TeV scale. The LHC will collide proton beams at a center–of–mass energy of 14 TeV with an interaction rate of 10^9 Hz. The ATLAS online selection will face the challenge of efficiently selecting interesting candidate events whilst rejecting the enormous number of minimum bias and QCD–jet background events reducing the bunch crossing rate of 40 MHz to around 200 Hz for permanent storage. The ATLAS trigger is performed in a three level selection: Level1, Level2 and the Event Filter; the last two are viewed as the High Level Trigger. In this thesis the High Level Trigger strategy and physics performance for the electron and photon selection and the potential to trigger on a Standard Model Higgs with electron and photon decays in the low mass region mH < 2mZ has been evaluated. In addition, to validate the electron trigger selection the electron/pion separation capability with the High Level Trigger has been studied with real data from the ATLAS Combined Test Beam 2004.