The antiproton/proton ratio

Measurement of the antiproton abundance in the cosmic radiation bears strongly on questions ranging from the possibility of a baryon symmetric universe to characterizing the origin and transport of the cosmic rays. However, the interpretation of cosmic ray antiproton measurements has been very uncertain ever since their discovery by Golden et at [Golden 79]. While antiprotons in the cosmic radiation are expected as "secondary" products of interactions of the primary cosmic radiation, principally protons, with the ambient interstellar medium (ISM) [2, Webber&Potgieter 89, Gaisser&Schaefer 92], the first positive measurements [Golden 79,Bogomolov 90, Buffington 82] reported higher antiproton fluxes than predicted by contemporary models of cosmic ray transport. Of the numerous explanations proposed (reviewed in Stephens and Golden [7]), one class assumed that secondary antiprotons are produced by cosmic ray protons and helium which have passed through more matter than implied by measured secondary/primary ratios of heavier elements (e.g., boron/carbon). Others considered "exotic" sources such as the evaporation of primordial black holes, the decay of dark matter, or acceleration in relativistic plasmas. It was also suggested that the excess could be a manifestation of a baryon symmetric cosmology [8]. The largest discrepancy was at about 200 MeV [Buffington 82], where antiproton production in p-p interactions is heavily suppressed [7,9]; however, later measurements gave corresponding upper limits which were significantly lower [LEAP, PBAR].
The newest measurents from BESS, MASS2 , IMAX, and CAPRICE support the assumption that the majority of the antiprotons are secondary products. 

The antiproton/proton ratio at the top of the atmosphere.
The lines are calculations of interstellar antiprotons assuming a pure secondary production during the propagation of cosmic rays in the galaxy. Solid lines, upper an lower limit of the calculation: Simon, Molnar & Roesler (1998), dashed line: L.Bergstroem & P. Ullio (private communication)


The antiproton flux at the top of the atmosphere.
Solid lines, upper an lower limit of the calculation: Simon, Molnar & Roesler (1998), dashed line: L.Bergstroem & P. Ullio (private communication), dotted line: primary antiproton flux givenb by annihilation from neutralino from MSSM with a mass of 964 GeV;
Ullio (1999)

References Data points:

References theoretical calculations:


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