Upper Limit on the Abundance of Anti-protons in the Low Energy Galactic Cosmic Radiation

Abstract

THE existence of anti-matter in the universe has intrigued astrophysicists for quite some time. Several authors have suggested the existence and creation of anti-matter at various places in the universe^1,2. One way of attempting to verify such possibilities is to see if cosmic rays, which include nuclei accelerated from various regions of our galaxy (if not the whole universe), contain anti-nuclei. Alfven¹, however, argues that cosmic rays at the Earth may not contain anti-nuclei for various reasons. Even if this were so, cosmic rays should contain secondary anti-protons produced in collisions of cosmic ray protons with interstellar hydrogen. Estimates of the abundance of secondary anti-protons have been made by several authors: Fradkin³ gives a value (p̄/p)∼5 × 10⁻⁴ for anti-protons of energy E_p > 1.7 GeV; Milford and Rosen⁴ estimate that for E_p∼0.5 GeV, (p̄/p)⪍3 × 10⁻³ and more recently by calculating the energy spectrum of such anti-protons they state⁵ (the numbers are not published to my knowledge) that the ratio (p̄/p) at low energies may be greater by several orders of magnitudes than that calculated at high energies.