First cosmic ray results of the RPC commissioning in the ATLAS cavern

The first commissioning test of three muon towers of the ATLAS Muon Spectrometer, installed in the cavern, was carried out. The stations under test belong to the barrel sector 13, which is a large sector. A muon tower consists of three stations: the Inner, the Middle and the Outer, starting from the interaction point. The Barrel Inner Large (BIL) stations are constituted by MDT chambers; the Barrel Middle Large (BML) stations by MDTs assembled between two RPC chambers; and the Barrel Outer Large (BOL) stations by MDTs with only one RPC mounted downstream. Specific Level-1 trigger algorithms have been studied to trigger on cosmic rays and implemented to commission the muon stations. Comparison between the measured trigger rate and the simulated results will be presented. Moreover, the RPC performances have been studied by comparing the MDT track extrapolations with the firing RPC readout strips. The RPC detection efficiency is evaluated in the eta measuring view, resulting as a combination of gas volume efficiency and Front-End efficiency.