Observation of the GZK Cutoff by the HiRes Experiment
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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