On the reported detection of sub-GeV antiprotons in galactic cosmic rays

Abstract

Buffington et al.¹ claim to have detected a p̄/p ratio of 2.2±0.6 × 10⁻⁴ at energies between 130 and 320 MeV. This is several orders of magnitude above theoretical predictions^2–4 at these lower energies for p̄ fluxes resulting from collisions of primary cosmic rays with the interstellar gas. Measurements at higher energies by Golden et al.⁵ show a p̄/p ratio of 5.2±1.5 × 10⁻⁴, in excess, by a factor of about 3, of the expected values if p̄s are of secondary origin in the standard model of galactic cosmic rays. The reported H̄e/He ratio¹ is significantly lower than the reported p̄/p ratio, raising difficulties with some scenarios⁶ in which the p̄s are primary cosmic rays from anti-galaxies. Kiraly et al.⁷ suggest black hole evaporation as a p̄ source. I discuss here scenarios in which the reported sub-GeV p̄ excess might be produced as secondaries in high energy collisions. Such production must take place in compact, optically thick sources.