Abstract
RICH (Ring Imaging CHerenkov) counters for PID in the high momentum domain and in large acceptance experiments require photon detectors covering extended surface (several square meters) and able to accept Cherenkov photons in a wide angular range. The first generation of these detectors was based on the use of organic vapors.
The second generation consists of CsI photocathodes and open geometry gaseous detectors (MWPC). Some limits of the technique arise from the bombardment of the photocathodes by the ions generated in the amplification process and by the photon feedback.
A third generation of gaseous photon detectors using closed geometry, as those possible with multistage arrangements of micropattern gaseous detectors, can overcome the observed limitations.