Studies of a proximity focusing RICH with aerogel radiator for future Belle upgrade

We have been developing a proximity focusing ring imaging Cherenkov counter (RICH) with aerogel radiator, to extend the hadron identification capabilities in the forward endcap region of the Belle detector at the KEK B factory. This paper presents our recent studies on possible improvement of the RICH performance by using precise timing information. Cherenkov photons emitted in the aerogel radiator as well as in the entrance window of the PMT were used for the time-of-flight (TOF) measurement. A beam test using the Burle 85011 MCP PMT showed an excellent resolution of about 35 ps for Cherenkov photons from the PMT window. Such TOF measurement would supplement the RICH performance, and allow to positively identify particles below the Cherenkov threshold in aerogel, such as kaons and protons in the region around 1 GeV/c.