Study of a threshold Cherenkov counter based on silica aerogels with low refractive indices

To identify π± and K± in the region of 1.0−2.5 GeV/c, a threshold Cherenkov counter equipped with silica aerogels has been investigated. Silica aerogels with a low refractive index of 1.013 have been successfully produced using a new technique. By making use of these aerogels as radiators, we have constructed a Cherenkov counter and checked its properties in a test beam. The results obtained demonstrated that our aerogel was transparent enough to make up for loss of the Cherenkov photon yield due to a low refractive index. Various configurations for the photon collection system and some types of photomultipliers, such as the fine-mesh type, for a read out were also tested. From these studies, our design of a Cherenkov counter dedicated to πK separation up to a few GeV/c with an efficiency greater than 90% was considered.