The Production of Anti-Matter in our Galaxy

The discovery of a single anti-helium nucleus in the cosmic ray flux would definitely point toward the existence of stars and even of entire galaxies made of anti-matter. The presence of anti-nuclei in cosmic rays has actually profound implications on the fundamental question of the baryon asymmetry of the universe. It is therefore crucial to determine the amount of anti-matter which our own galaxy already produces through the spallation of high-energy protons on the interstellar gas of the galactic disk. We have used here a coalescence model to assess the amount of anti-deuterium and anti-helium 3 present in cosmic rays together with anti-protons. The propagation of cosmic rays in the galaxy is described through a two-zone diffusion model which correctly describes the observed abundances. We find that the antideuterium/proton ratio exceeds $10^{-9}$ above a momentum per anti-nucleon of about 4 GeV/c. Would the universe be purely made of matter, the AMS collaboration should be able to detect a few anti-deuterons during the space station stage of the experiment. However, the antihelium3/proton abundance does not exceed $4 10^{-13}$. Heavier anti-nuclei are even further suppressed.