A study of proximity focusing RICH with aerogel radiator

Proximity focusing RICH based on an aerogel Cherenkov radiator has been developed for a new particle identifier in the Belle upgrade. To further improve the detector performance, a new concept for Cherenkov ring imaging has been introduced, where multiple aerogel layers with different indices are accumulated to increase observed photoelectrons without making the single photon resolution worse. By constructing a prototype counter, this idea was validated in a test beam experiment, and we achieved 5.5σπ/K separation at 4GeV/c. In addition, the potential of the time-of-flight capabilities to detect time information of Cherenkov photons, where a micro-channel plate PMT is employed as a photodetector, was examined in a beam test, and excellent performance of this technique was obtained.