MEASUREMENT OF 0.25-3.2 GEV ANTIPROTONS IN THE COSMIC-RADIATION

The balloon-borne Isotope Matter-Antimatter Experiment (IMAX) was flow n from Lynn Lake, Manitoba, Canada on 16-17 July 1992. Using velocity and magnetic rigidity to determine mass, we have directly measured the abundances of cosmic ray antiprotons and protons in the energy range from 0.25 to 3.2 GeV. Both the absolute flux of antiprotons and the an tiproton/proton ratio are consistent with recent theoretical work in w hich antiprotons are produced as secondary products of cosmic ray inte ractions with the interstellar medium. This consistency implies a lowe r limit to the antiproton lifetime of similar to 10(7) yr.