Overview on production and first results of the tests on the RPCs for the ALICE dimuon trigger

The trigger for the ALICE muon spectrometer will be issued by single-gap, low-resistivity bakelite RPCs. The trigger detector will be made of four 6×6 m2 RPC planes arranged in two stations, for a total of 72 chambers. Strip planes, stiffener planes and mechanical supports are realized and assembled in the INFN Technological Laboratory in Torino (Italy). All the produced volumes are tested before installation in ALICE: gas tightness and spacer gluing are checked at INFN-LNGS, while INFN-Torino Laboratory houses the cosmic rays test station. The tests are made with the ALICE streamer mixture (50.5% Ar, 41.3% C2H2F4, 7.2% i-C4H10, 1% SF6) and include measure of the electrodes resistivity, together with noise and efficiency mapping. These tests provide a complete characterization of the detectors (efficiency, cluster size, absorbed current, noise rates).