Selection of high-pT electromagnetic clusters by the Second Level Trigger of ATLAS

In a scheme being considered for the Atlas Second Level (LVL2) trigger, the electron and photon triggers share the selection of electromagnetic clusters. This selection takes as an input the Region-of-Interest information passed from the LVL1 trigger and refines it using the full granularity information of the calorimeter. This information is in turn used to calculate shower-shape quantities, which together with the cluster transverse energy information, discriminate electromagnetic clusters from jets. This note summarizes the performance, in terms of rates and efficiencies, of the LVL2 trigger electromagnetic Feature-Extraction algorithm. Both low and design luminosity results are presented. Particular emphasis is given to the optimization of the trigger selection cuts and to the sequence of trigger selection steps.