RESULTS FROM BEAM TESTS OF THE CAPRICE RICH DETECTOR

A compact RICH counter using a solid NaF radiator and pad readout has been developed and tested in particle beams. The good transmission of the optical elements together with a low noise level in the electronics results in a large number of detected photoelectrons per event. More than 20 photoelectrons are detected per event for Z = 1 particles with beta > 0.9 at perpendicular incidence. The reconstructed Cherenkov angle has a resolution of 4.2 mrad at perpendicular incidence (beta = 0.9-1) and 19 mrad at 30-degrees incidence angle. For light ions (Z < 10) a good charge resolution is possible by measuring the total charge induced by the Cherenkov light. The large number of detected photoelectrons (up to 1000 per event) also allows isotope separation over a wide energy range. The RICH detector will be an important part of a balloon borne experiment, CAPRICE, to measure the flux of antiprotons, positrons and light isotopes in cosmic radiation as well as to continue the search for antinuclei.