First observation of the Greisen-Zatsepin-Kuzmin suppression.
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 observe the ankle of the cosmic-ray energy spectrum as well, at an energy of 4 x 10(18) eV. We describe the experiment, data collection, and analysis and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.
Abbasi
R U
RU
Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA.
Abu-Zayyad
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Allen
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Amman
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Archbold
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Belov
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Belz
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Ben Zvi
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Bergman
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Blake
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Brusova
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Fedorova
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Gray
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Hanlon
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Hoffman
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Jones
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Jui
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Kim
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Kirn
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Loh
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Manago
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Martens
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Matthews
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Matthews
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Moore
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O'Neill
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Reil
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Riehle
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Rodriguez
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Sasaki
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Smith
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Sokolsky
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Springer
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Thomas
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Thomson
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Westerhoff
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Wiencke
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