Study of a silica aerogel for a Cherenkov radiator

Highly transparent silica aerogel has been developed for a Cherenkov radiator in a RICH detector to be installed into the Belle forward end-cap apparatus. We have improved the aerogel optical properties for a wide range of refractive indices around 1.03–1.07. The parameters that control a synthesis process in the aerogel production were successfully optimized, and the obtained transmission length for this index range was almost doubled. A prototype was constructed using newly produced aerogel samples in order to carry out a test beam experiment, and a remarkable increase in the Cherenkov light yield was confirmed. The uniformity of refractive index in an aerogel block was examined using an X-ray tomography device and the deviation was found to be sufficiently small. Furthermore, the production of a monolithic aerogel consisting of two layers with different refractive indices is also described.