A. Bressan

University of Trieste and Sezione INFN di Trieste, Trieste, Italy
on behalf of the COMPASS RICH group


     COMPASS RICH-1 is a large acceptance gaseous RICH using 3 m of C4F10 as radiator and MWPCs with CsI photocathodes as VUV Photon Detectors, for a total active surface of about 5.5 m2. The 83 thousand channels equipped with analog read-out electronics are read via large front-end boards with local intelligence able to stand high band width. The image focalisation is provided by a large UV mirror wall ( 20 m2). π /K separation up to 60 GeV/c is foreseen.
     The main characteristics of the detector are the large acceptance resulting in very large transversal dimensions, the use of far UV Photon Detectors, which implies UV transparencies of the radiator gas, namely high gas purity, UV transparency of the windows between the radiator volume and the photon detectors, good UV mirror reflectance and high rate capabilities, made possible by the clever design of the read-out system.
    RICH-1 is one of the key detectors of the COMPASS experiment at CERN. COMPASS Physics program includes the study of the spin structure of the nucleon with polarised semi-inclusive DIS measurements using the SPS muon beam and the study of hadron spectroscopy, in particular in the charm sector, using hadron beams. Both Physics goals require PID in a wide momentum range, in crowded environments and large luminosities. The detector, as well as the whole COMPASS spectrometer, has been commissioned during year 2001.
     We give a description of the detector and first hints about its performances as well as a report about various technological achievements required by this challenging project.