The cosmic-ray antiproton flux between 3 and 49 GeV

We report on a new measurement of the cosmic ray antiproton spectrum. The d ata were collected by the balloon-borne experiment CAPRICE98, which was flo wn on 1998 May 28-29 from Fort Sumner, New Mexico. The experiment used the NMSU-WiZard/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas Ring Imaging Cherenkov (RICH) detector, a time-of-flight system, a trackin g device consisting of drift chambers and a superconducting magnet, and a s ilicon-tungsten calorimeter. The RICH detector was the first ever flown cap able of mass-resolving charge-one particles at energies above 5 GeV. A tota l of 31 antiprotons with rigidities between 4 and 50 GV at the spectrometer were identified with small backgrounds from other particles. The absolute antiproton energy spectrum was determined in the kinetic energy region at t he top of the atmosphere between 3.2 and 49.1 GeV. We found that the observ ed antiproton spectrum and the antiproton-to-proton ratio are consistent wi th a pure secondary origin. However, a primary component may not be exclude d.