Triggering Top Quark Events

Collisions at the LHC occur at a rate of up to 40 MHz, much larger than the 200 Hz storage capacity of the ATLAS experiment. The ATLAS trigger system has the challenging task of rejecting 99.9995 % of the events produced in collisions, while keeping those needed to achieve the physics goals of the experiment. This note evaluates the expected performance of the trigger system in top quark events by investigating the response of the trigger system to single objects such as a muon, an electron or a jet originating from top quark decays. In addition, the methodology needed to efficiently select top quark events in the online trigger system is discussed including methods to determine trigger efficiencies from data.