PERFORMANCE OF A PROTOTYPE RICH DETECTOR USING A CSI PHOTOCATHODE READOUT WITH LOW-PRESSURE AVALANCHE

A UV-sensitive wire chamber with a CsI photocathode was tested to exam ine the overall performance, and the quantum efficiency of the cathode . The chamber is operated as a parallel plate avalanche counter (PPAC) at low pressure (35 Ton ethane). A detailed discussion of our ''imple mentation-ready'' design is followed by a description of the CsI-coati ng procedure. We measured, on the bench, a quantum efficiency of 23 +/ - 4% at 188 nm. The UV-chamber was tested as a RICH (ring imaging Cher enkov) focal plane detector using a 1 GeV/c electron beam from the AGS at BNL. The measured yields of photoelectrons from Cherenkov light we re 3.3, 5.9 and 7.4 photoelectrons per ring per meter using nitrogen, methane and ethane radiators. The quantum efficiency measured on the b ench and deduced from the beam test is in good agreement with the lite rature. These results are quite promising for building a large area RI CH focal plane using this technique, e.g. in the PHENIX RICH detector to be built at RHIC.