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 examine 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 Torr ethane). A detailed discussion of our "implementation-ready" design is followed by a description of the CsI-coating 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 Cherenkov) focal plane detector using a 1 GeV/c electron beam from the AGS at BNL. The measured yields of photoelectrons from Cherenkov light were 3.3, 5.9 and 7.4 photoelectrons per ring per meter using nitrogen, methane and ethane radiators. The quantum efficiency measured on the bench and deduced from the beam test is in good agreement with the literature. These results are quite promising for building a large area RICH focal plane using this technique, e.g. in the PHENIX RICH detector to be built at RHIC.