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Dip in UHECR spectrum as signature of proton interaction with CMB

V. Berezinsky·A. Z. Gazizov·S. I. Grigorieva
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Abstract

Ultrahigh energy (UHE) extragalactic protons propagating through cosmic microwave radiation (CMB) acquire the spectrum features in the form of the dip, bump (pile-up protons) and the Greisen-Zatsepin-Kuzmin (GZK) cutoff. We have performed the analysis of these features in terms of the modification factor. This analysis is weakly model-dependent, especially in case of the dip. The energy shape of the dip is confirmed by the Akeno-AGASA data with $χ^2=19.06$ for d.o.f. =17 with two free parameters used for comparison. The agreement with HiRes data is also very good. This is the strong evidence that UHE cosmic rays observed at energies $1\times 10^{18}$ eV - $4\times 10^{19}$ eV are extragalactic protons propagating through CMB. The dip is also present in case of diffusive propagation in magnetic field.

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V. Berezinsky, A. Z. Gazizov, S. I. Grigorieva. 2005-02-28. Dip in UHECR spectrum as signature of proton interaction with CMB. https://doi.org/10.1016/j.physletb.2005.02.058

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