RICH photon detector module based on geiger-mode APDs

The possibilities offered by Geiger-mode APDs, also known as silicon photomultipliers, for detection of Cherenkov photons emitted by pions in an aerogel radiator, have been investigated. The main issue is the detection of single photons in the relatively high background of noise pulses. A suitably narrow coincidence time window eliminates most of this background, while the use of light concentrators increases the acceptance, i.e. the sensitivie surface over which Cherenkov photons are collected. With such techniques, we have measured a number corresponding to 3.7 detected photons per ring. However, a thicker radiator and other improvements of the experimental apparatus, might increase this figure for a factor of 10. Such a ring imaging Cherenkov detector would then meet the requirements for particle identification inside the upgraded Belle spectrometer.