ATLAS RPC certification with cosmic rays

Almost one-third of the 1116 resistive plate chamber (RPC) units installed in the ATLAS experiment was tested and certified at the Lecce Cosmic Ray Testing Facility. About half of these units belong to the same chamber typology named barrel outer small (BOS). This large and nearly homogeneous sample allowed to perform an extensive study of the detector behavior and characteristics. The intrinsic spread of the chamber parameters was extracted after correction for known pressure and temperature effects. A residual dependence on pressure and temperature has been found and empirically corrected. The distribution of gas gap and panel efficiencies, cluster sizes (CSs), single rates and dark currents versus the applied threshold and high voltage was measured. An optimal working point was defined for each gas volume and the distribution of all relevant parameters was studied at the average working point for different voltage threshold. This work shows that the single unit BOS ATLAS RPC meets the experiment requirements.