A FAST-CATHODE PAD-PHOTON DETECTOR FOR CHERENKOV RING IMAGING

Fast ring imaging Cherenkov counters, with pad readout for unambiguous image reconstruction, are considered for use in a high luminosity environment. The quantum efficiency of several new photosensitive gases (TMA and DMA) are measured and compared to the known standard gases (TEA and TMAE). A solid CsI/TMAE reflective photocathode is also considered as an alternative fast and efficient photosensor. A detailed experimental investigation has been made of a multiwire photon detector with TEA as the photosensitive converter. This detector, designed as part of a fast RICH counter for a B factory electron-positron collider, may also be used at hadron colliders as well as at fixed target facilities. These tests allowed the optimization of relevant construction parameters to fulfill the requirements of speed (sigma(t) < 10 ns), cathode pad detection efficiency (epsilon(c) > 0.98) and pixel error (sigma(x) < 1.5 mm) over the full surface of the detector. Its performance was used to tune the parameters of a general Monte Carlo simulation program in order to predict the response of a photodetector with various photoconverters and pad sizes.