Low energy antiprotons in the cosmic rays: A new upper limit

Abstract

Kinematics predicts the severe suppression of low-energy (<1 GeV) secondary antiprotons in the Galactic cosmic rays. Thus the observation several years ago of a finite flux of low-energy antiprotons could not be explained with existing models of cosmic ray propagation, which led to a plethora of theoretical speculation. We have recently flown a balloon-borne instrument to measure the energy spectrum of cosmic-ray$\bar p's$, and have found no antiprotons in the energy interval 200–640 MeV (corrected to the top of the atmosphere). This yields an upper limit to the$\bar p/p$ ratio of 5.5×10⁻⁵ (90% confidence level), well below and hence contradicting the earlier result.