Measurement of electron production from cosmic rays in the ATLAS detector

The special topology of cosmic events traversing all subdetectors offers the unique opportunity to investigate the combined performance of the ATLAS detector in identifying and reconstructing particles before first proton collisions at the LHC. Through interaction with the inner detector material or through decays high-energy electrons can be produced from the traversing cosmic muons. A sample of 3.5 million cosmic ray events with a high-level trigger track candidate in the central part of the inner detector is used as a basis to extract the electrons from the different processes. To separate the electrons from the large background of muon bremsstrahlung among the about 10000 candidates, the characteristic properties of electrons in the detector are exploited accounting for the special nature of cosmic events. The resulting extraction of about 34 electrons mainly originating from ionisations enables an observation and investigation of real electrons in the ATLAS detector for the first time.