Electron Trigger Studies for the Event Filter of the ATLAS Detector at the Large Hadron Collider

In 2006 the Large Hadron Collider (LHC) with a center-of-mass energy of $14\TEV$ will be operational at CERN near Geneva. It will offer new experimental insights at the TeV-energy scale. The long awaited Higgs particle might be found, filling the last gap in the Standard Model. New theories like the Supersymmetry or Supergravity can be testified. The unprecedented luminosity of $10^{34}\LUM$ and the large QCD background will pose stringent requirements to the detectors at LHC. The online selection of rare interesting events within the tremendous amount of particles crossing the detectors is challenging. In this thesis, a first study of the high-Pt single electron trigger at the event filter of ATLAS - the third and last online selection step - is presented. An overall trigger efficiency of 70%(66%) for single electrons with Pt=30(20)GeV at design (low) luminosity within the stringent time constraints of the online system can be achieved. The single electron trigger rate is about 80(25)Hz of which 65%(50%) are due to irreducible processes like W -> e nu. The high trigger rate for single electrons compared to the total target rate of 100Hz is of big concern. Therefore it might be necessary to raise the threshold for single object triggers and to pre-scale the lower threshold trigger items. A case study using the physics channels W -> e nu, Z -> e e, and H -> 4e will give an indication how double object trigger items or the missing transverse energy can be used to save the trigger efficiency while reducing the trigger rate.