Proximity focusing RICH with flat panel PMT as photon detector and aerogel as radiator

Using aerogel as radiator and 64-channel flat panel multi-anode PMTs (Hamamatsu H8500) for photon detection, a proximity focusing Cherenkov ring imaging detector has been constructed and tested in the KEK π2 beam. The single photon resolution obtained in the tests (typically around 14 mrad) is well approximated by estimates of contributions from pixel size and emission point uncertainty. The number of detected photons per Cherenkov ring, typically about 6 for a 2 cm thick aerogel radiator tile, is in good agreement with estimates based on aerogel and detector characteristics. The detector allows a very efficient separation of kaons and pions at 4GeV/c.