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Observation of the GZK Cutoff by the HiRes Experiment

G. B. Thomson

astro-pharXiv:astro-ph/0609403

Abstract

The High Resolution Fly's Eye (HiRes) experiment has observed the GZK cutoff. HiRes' measurement of the flux of cosmic rays shows a sharp suppression at an energy of 6 x 1019 eV, exactly the expected cutoff energy. We observe the ``ankle'' of the cosmic ray spectrum as well, at an energy of 4 x 1018 eV. We describe the experiment, data collection, analysis, and estimate the systematic uncertainties. The results are presented and the calculation of a five standard deviation observation of the GZK cutoff is described.

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