Threshold aerogel Cherenkov detector with Fresnel lens focalization

Our aim is to optimize an aerogel threshold detector for the smallest possible diameter of PMT. We optimize the light collection using the focalization of the Cherenkov light with a Fresnel lens. The beam of photons is then sent onto a mirror to be reflected to the PMT. We have built and tested a first prototype with a 10 × 10 × 10 cm 3 aerogel radiator of n = 1.03 . The first results of these measurements, obtained with a 1.5 in. fine mesh PMT are shown.