Determination of electron trigger efficiencies using Z ---> e e events at the LHC

The ATLAS experiment has designed a three-level trigger system in order to reduce the LHC bunch crossing frequency of 40 MHz to O(100 Hz ) which can be recorded. For several key measurements a good understanding of the performance of the trigger system is needed. In this thesis a method for the determination of electron trigger efficiencies from Z 0 → e +e − events, called Tag&Probe; , is presented. Results obtained by this method from simulated events are presented, including a detailed study of the electron trigger performance and a discussion of possible error sources of the method. It is demonstrated that the efficiencies as obtained from the Tag&Probe; method can be used to correct corresponding inefficiencies in other physics processes using the example of leptonic tt decays.