Evidence for the Existence of Cosmic-Ray Antiprotons

Abstract

A search for cosmic-ray antiprotons was recently performed with use of a balloon-borne superconducting-magnet spectrometer. A total of 46 antiproton candidates were observed in the rigidity interval from 5.6 to 12.5 GV/c. Of these events 18.3 are expected to be atmospheric and instrumentation background. The $\frac{\overline{p}}{p}$ ratio is found to be (5.2\ifmmode\pm\else\textpm\fi{}1.5) \ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$. This ratio is consistent with secondary production of antiprotons in the interstellar medium.