Study of highly transparent silica aerogel as a RICH radiator

We have developed silica aerogel to be employed as a RICH radiator in the Belle PID upgrade. For this purpose, new aerogel sample with a higher refractive index (n) of ∼1.05 was successfully produced while keeping the hydrophobic feature. In this novel technique, a new solvent was introduced in the first step of the sol-gel process so as to avoid a deterioration of the optical quality, even for n greater than 1.03. Based on this procedure, the transmission length was obtained to be more than 40 mm at 400 nm wave length, which was twice longer than before, for samples of ∼100×100×10mm3 size. In this article, the results of the new aerogel production will be shown together with some design considerations for the RICH radiator.