First results of the cosmic rays test of the RPC of the ATLAS muon spectrometer at LHC

The trigger for the Barrel Muon Spectrometer of the ATLAS experiment at LHC will be given by means of Resistive Plate Chambers working in avalanche mode. Before being mounted on the experimental apparatus each RPC chamber will undergo detailed quality control tests. A dedicated cosmic rays test station with good tracking resolution is operational in Naples University and INFN laboratory. All working parameters of RPCs are monitored and measured. Moreover, the uniformity of the efficiency on the whole surface is measured. A brief description of the test station and results for the first 148 Units will be presented