Isotropy of Cosmic Rays beyond 1020eV Favors Their Heavy Mass Composition

Collaboration
Jun 27, 2024
8 pages
Published in:
  • Phys.Rev.Lett. 133 (2024) 4, 041001
  • Published: Jul 22, 2024
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Abstract: (APS)
We report an estimation of the injected mass composition of ultrahigh energy cosmic rays (UHECRs) at energies higher than 10 EeV. The composition is inferred from an energy-dependent sky distribution of UHECR events observed by the Telescope Array surface detector by comparing it to the Large Scale Structure of the local Universe. In the case of negligible extragalactic magnetic fields (EGMFs), the results are consistent with a relatively heavy injected composition at E10EeV that becomes lighter up to E100EeV, while the composition at E>100EeV is very heavy. The latter is true even in the presence of highest experimentally allowed extragalactic magnetic fields, while the composition at lower energies can be light if a strong EGMF is present. The effect of the uncertainty in the galactic magnetic field on these results is subdominant.
Note:
  • 8 pages, 3 figures, accepted for publication in PRL