Performance evaluation of silica aerogel cherenkov counters with n≫1.08

It is need threshold type Cherenkov counters with the refractive index of about 1.1 to identify protons from kaons and pions in the momentum range of 1-2 GeV/c in a trigger stage. There were no materials having such refractive indices in ordinary temperature and ordinary pressure. But we found the production method of silica aerogel with high refractive indices. (2005NSS N14-191) By our research and development works of two years, production parameters were modified and transmission length at the wavelength of 400 nm achieved more than 20 mm at index range of 1.08<n<1.25. We will perform the beam test experiments with the electron beams (LNS, Tohoku Univ.) in May and September, and the proton beams (HIMAC, NIRS) in this autumn. We will report the results in this presentation.