Heavy Cosmic Ray Nuclei from Extragalactic Sources above ‘The Ankle’

ABSTRACT

A recent observation by the Auger Observatory group presents evidence for cosmic rays above 5.6 x 1019 eV -(56 EeV) being ‘predominantly protons’ coming from Active Galactic Nuclei. If, as would be expected, the particles above the ankle at about 2 EeV are almost all of Extragalactic origin then it follows that the characteristics of the nuclear interactions of such particles would need to be very different from conventional expectation – a result that follows from the measured positions of ‘shower maximum’ at somewhat lower energies where mass measurements using conventional nuclear interaction models indicate (ln A) ~ 2.5. Such a claim is rather dramatic.

In our own analysis we study to what extent the Auger results could, indeed, give such a mean value for (ln A)rather than a much smaller one. We conclude that they can, and the need for a dramatic change in the nuclear physics disappears.

PACS numbers: 96.50.sb, 96.50.sd, 98.70.Sa.