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,
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 ), 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 . 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
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
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;
References Data points:
R. L. Golden et al. Phys. Rev. Lett. 43, 1196 (1979);
R. L. Golden et al., Astrophys. Lett.., 24 (1984) 75
A. Buffington et al., Ap. J., 248, 1179 (1981)
A. Buffington and S.M. Schindler, Astrophy. J.248, L105 (1981).
E. A. Bogomolov et al, in Proc. 16th Int. Cosmic Ray Conf., Kyoto 1, 330
E. A. Bogomolov et al, in Proc. 20th Int. Cos. Ray Conf., Moscow 2, 72
E. A. Bogomolov et al, in Proc. 21st Int. Cos. Ray Conf., Adelaide 3, 288
S. P. Ahlen et al., Phys. Rev. Letters 61, 145 (1988)
M.H. Salamon et al, Astrophy. 1. 349, 78 (1990).
R. Streitmatter, Proc. 21th Int. Cosmic Ray Conf. (Adelaide), 3, 277
S.J. Stochaj. Ph.D. thesis, University of Maryland, 1990;
R. E. Streitmatter er at, Adv. Space Research 9, 1265 (1989).
W. Mitchell et al., Phys Rev. Lett. 76, 17, 22 Apr. 1996
Boezio et al., Astrophysical Journal 487 415-423 (1997)
et al., preprint astro-ph 0103513, submitted to ApJ
Webber & Potgieter
R. Webber and M. S. Potgieter, ApJ 344, 779 (1989)
Gaisser & Schaefer 92: T.
K. Gaisser and R. K. Schaefer, ApJ 394, 174 (1992)
M. Simon, A.
Molnar and S. Roesler, ApJ 499, 250 (1998)
: T. K. Gaisser and R. H. Maurer, Phys. Rev. Lett. 30, 1264
: S. A. Stephens and R. L. Golden, Space Science Rev. 46.
: F. W. Stecker, in Progress in Cosmology. edited by A. W. Wolfendale
(D. Reidel Publishing, Dordrecht, 1982), p.1.
: M. Simon and U. Heinbach, in Cosmic Rays. Supernovae and the
Interstellar Medium, edited by M. M. Shapiro et al (Kluwer Academic Publishers,
Dordrecht, 1991). p.137
P. Ullio, 1999, astro-ph/9904086
Back to Astrophysics