Evolution of the RICH technique

This paper presents recent advances in development of Ring Imaging Cherenkov counters. Work on bare and protected reflective CsI photocathodes is reviewed and compared with gaseous UV photosensors. Development of multipixel-visible light-vacuum photosensors allows much improved Cherenkov angular resolution (by factor 10) relative to the available gaseous UV photosensors. The Hybrid PhotoDiode and MultiAnode PMT concepts are reviewed with prototype realizations described and test results compared with expectations. The use of the Gas Electron Multiplier (GEM) with gaseous RICH counters is presented and discussed. Its advantages for single electron detection are shown by new experimental data.