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The High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of 6 x 10(19) eV, consistent with the expected cutoff energy. We(More)
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 × 10 19 eV, exactly the expected cutoff energy. We observe the " Ankle " of the cosmic ray spectrum as well, at an energy of 4 × 10 18 eV. We describe the experiment, data collection,(More)
Air-fluorescence detectors such as the High Resolution Fly's Eye (HiRes) detector are very sensitive to upward-going, Earth-skimming ultrahigh energy electron-neutrino-induced showers. This is due to the relatively large interaction cross sections of these high-energy neutrinos and to the Landau-Pomeranchuk-Migdal (LPM) effect. The LPM effect causes a(More)
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