Antiproton spectrum in cosmic rays

Abstract

The steady-state antiproton spectrum in cosmic rays as a result of the collision between primary cosmic protons and interstellar hydrogen is calculated by means of the statistical model of two fireballs in multiple-particle production. Results based on Fermi’s original one-fire-ball model are also presented for comparison. We found that the antiprotons obey approximately a power law with an exponent about 2.6 which is about (the same magnitude) equal to the exponent of the general cosmic rays spectrum. The numerical value of the exponent is found to be determined principally by the exponent of the cosmic protons, and very insensitive to the parameters of the two-fire-ball model introduced in the calculation. A closed expression of the ratio of the number densities of these secondary antiprotons to cosmic protons is expressed in terms of the proton exponent, interstellar hydrogen density, total p-p inelastic cross-section, antiproton lifetime in the Galaxy and the twofire-bal parameters. The numerical values of the ratio range from about 3.8·10x2212;3 at 1012eV to 6.8·10−4 at 1018 eV.