Heavy Cosmic Ray Nuclei from Extragalactic Sources above 'The Ankle'

TL;DR

This paper challenges recent claims that ultra-high-energy cosmic rays are primarily protons from active galactic nuclei, presenting evidence that they are likely heavy nuclei, thus not requiring new nuclear physics models.

Contribution

The study provides an alternative analysis indicating cosmic rays above the ankle are still heavy nuclei, countering claims of a transition to proton dominance and eliminating the need for new nuclear physics assumptions.

Findings

Cosmic rays above 2 EeV are likely heavy nuclei with <ln A> = 2.2 +- 0.8.

Analysis contradicts recent claims of proton dominance from AGN sources.

No dramatic change in nuclear physics is necessary based on the data.

Abstract

A very recent observation by the Auger Observatory group claims strong evidence for cosmic rays above 56 EeV being protons 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' in the Auger' work. Our own analysis gives a different result, viz that the detected particles are still 'massive' specifically with a mean value of <ln A> = 2.2 +- 0.8. The need for a dramatic change in the nuclear physics disappears.