RICH with multiple aerogel layers of different refractive index

A proximity focusing ring imaging Cherenkov detector with multiple aerogel radiator layers is studied. In situations where limited space is available and a compact RICH detector is required, the use of a nonhomogeneous, multiple refractive index radiator offers a possibility for improving the resolution. Experimental investigations of the relevant parameters, i.e. single photon Cherenkov angle uncertainty and number of detected photons per ring, are presented for different aerogel radiator configurations. The results are promising and appear to satisfy the requirements for the forthcoming upgrade of the particle identification system of the Belle detector.