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 electronic s results in a large number of detected photoelectrons per event. More than 20 photoelectrons are detected per event for Z = 1 particles wit h beta > 0.9 at perpendicular incidence. The reconstructed Cherenkov a ngle 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 < 1 0) a good charge resolution is possible by measuring the total charge induced by the Cherenkov light. The large number of detected photoelec trons (up to 1000 per event) also allows isotope separation over a wid e energy range. The RICH detector will be an important part of a ballo on borne experiment, CAPRICE, to measure the flux of antiprotons, posi trons and light isotopes in cosmic radiation as well as to continue th e search for antinuclei.