The Cosmic-Ray Antiproton Flux between 0.62 and 3.19 GeV Measured Near Solar Minimum Activity

We report on the absolute antiproton flux and the antiproton to proton ratio in the energy range 0.62-3.19 GeV at the top of the atmosphere, measured by the balloon-borne experiment CAPRICE flown from Lynn Lake, Manitoba, Canada, on 1994 August 8-9. The experiment used the New Mexico State University WiZard/CAPRICE balloon-borne magnet spectrometer equipped with a solid radiator Ring Imaging Cherenkov (RICH) detector and a silicon-tungsten calorimeter for particle identification. This is the first time a RICH is used together with an imaging calorimeter in a balloon experiment, and it allows antiprotons to be clearly identified over the rigidity range 1.2-4 GV. Nine antiprotons were identified in the energy range 0.62-3.19 GeV at the top of the atmosphere. The data were collected over 18 hr at a mean residual atmosphere of 3.9 g cm^-2. The absolute antiproton flux is consistent with a pure secondary production of antiprotons during the propagation of cosmic rays in the Galaxy.