A closer look at the tertiary production of antiprotons in the Galaxy

Abstract

Antiproton spectrum in cosmic rays, produced by the interactions of cosmic-ray nucleons with interstellar gas, has a peak around 2 GeV with a steep positive slope below 1 GeV at production. During the propagation of antiprotons in the Galaxy, the low energy spectrum gets modified due to ionization loss and by the energy degradation from deep-inelastic interactions. In recent years, it is believed that the latter is a dominant process in creating more low energy antiprotons. In this paper, the available data on total, elastic, annihilation and charge-exchange cross-sections at accelerator energies are carefully examined to show that the above conclusion is based partly due to incorrect parametrization of the data and partly by including charge-exchange cross-section as part of deep-inelastic process. It is shown that the deep-inelastic cross-section in ( p ¯ , p ) interactions starts decreasing faster than for ( p, p) interaction below 10 GeV due to the opening of the annihilation channel. It has a low energy cut-off at the threshold energy for pion production as in the case of protons. Though the charge-exchange process play an important role at low energies, the energy change during this process is marginal as in the case of elastic scattering and hence does not contribute to the production of tertiary antiprotons.