X. Workshop on Resistive Plate Chambers and Related Detectors

OPERA is an experiment dedicated to the observation of numu into nutau oscillations through tau appearance on the CNGS beam. The experiment is composed by two identical super-modules, each with a target section (made of emulsion/lead bricks alternated to a scintillator Target Tracker) and a muon spectrometer (instrumented with bakelite RPCs and drift tubes). The RPCs are operated in streamer mode with the gas mixture Ar/C2H2F4/isoC4H10/SF6=75.4/20/4/0.6. The performances of the RPC system are presented. The sample of events induced by the CNGS neutrino beams as well as a large sample of cosmic rays have been used to study general properties of streamer-operated RPCs. The aging status of the detector, after four years of operation, is also described.