Operations and performance of the Resistive Plate Chambers detector supplying the first Level trigger in the barrel muon spectrometer of the ATLAS Experiment.

On Friday September 18th, the access mode in the ATLAS pit and galleries changed to “controlled” mode: the operations in view of the LHC switch on and incoming runs of the experiment are starting. In the meanwhile data taking in the experiment is going on in order to test and debug the whole systems, from detectors to the data acquisition chain, using cosmic rays as physical events. The Level-1 Muon Trigger in the barrel section of the muon spectrometer is, consequently, in a “warm” phase: its response and performance must be verified. The principles of operation of the trigger based on fast tracking with Resistive Plate Chambers is presented together with performance studies of the detectors made with cosmic ray muons traversing the ATLAS spectrometer.