Secondary antiproton production in relativistic plasmas

Recent measurements1–3 of the low-energy flux of antiprotons (\[pmacr]) in cosmic rays give ratios of \[pmacr]/p which are greater by a factor of 3–5 than predicted by the simple ‘leaky box’ model of cosmic-ray propagation. Here we report on an investigation of the possibility that the low-energy \[pmacr] excess reflects an origin in p–p collisions in relativistic plasmas. Because of both target and projectile motion in such plasmas, the antiproton production threshold in the frame of the plasma is much lower than the threshold of antiproton production in cosmic ray interactions with ambient matter. The spectrum of the resultant antiprotons therefore extends to much lower energy than in the cosmic ray case. Sites at which matter is accreted by compact objects could be sources of the low energy antiprotons. Escape of the antiprotons could be mediated by antineutron production.