T. Fukushima

A novel type of proximity focusing RICH counter with multiple refractive index aerogel radiator

Abstract A proximity focusing ring imaging Cherenkov detector, with the radiator consisting of two or more aerogel layers of different refractive indices, has been tested in 1 – 4 GeV / c pion beams at KEK. Essentially, a multiple refractive index aerogel radiator allows for an increase in Cherenkov photon yield on account of the increase in overall radiator thickness, while avoiding the simultaneous degradation in single photon angular resolution associated with the increased uncertainty of the emission point. With the refractive index of consecutive layers suitably increasing in the downstream direction, one may achieve overlapping of the Cherenkov rings from a single charged particle. The impact of the observed improvement on the π / K separation at the upgraded Belle detector is discussed.

Development of silica aerogel with any density

New production methods of silica aerogel with high and low refractive indices have been developed. A very slow shrinkage of alcogel at room temperature has made possible producing aerogel with high refractive indices of up to 1.265 without cracks. Even higher refractive indices than 1.08, the transmission length of the aerogel obtained from this technique has been measured to be about 10 to 20 mm at 400 nm wave length. A mold made of alcogel which endures shrinkage in the supercritical drying process has provided aerogel with the extremely low density of 0.009 g/cm3, which corresponds to the refractive index of 1.002. We have succeeded producing aerogel with a wide range of densities

Study of RICH Counter with Silica Aerogel Radiator

A proximity focusing RICH using aerogel as the Cherenkov radiator is being developed as a new particle identification device for the Belle detector upgrade. A prototype counter was constructed with recently produced aerogel samples, arranged in a focusing configuration, and a test beam experiment was carried out in order to evaluate the performance of the apparatus. With this device we have achieved a pi-K separation that exceeded 5sigma at 4 GeV/c, with ap9 detected photoelectrons per track. We have also studied the influence of various parameters like radiator refractive index combinations on the performance of the apparatus.