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Measurement of the cosmic-ray energy spectrum above 2.5×1018eV using the Pierre Auger Observatory

A. Aab et al. (The Pierre Auger Collaboration)
Phys. Rev. D 102, 062005 – Published 16 September 2020
Physics logo See Viewpoint: The Anatomy of Ultrahigh-Energy Cosmic Rays

Abstract

We report a measurement of the energy spectrum of cosmic rays for energies above 2.5×1018eV based on 215,030 events recorded with zenith angles below 60°. A key feature of the work is that the estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above 5×1019eV. The principal conclusions are

(1) The flattening of the spectrum near 5×1018eV, the so-called “ankle,” is confirmed.

(2) The steepening of the spectrum at around 5×1019eV is confirmed.

(3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index γ of the particle flux (Eγ) changes from 2.51±0.03(stat)±0.05(syst) to 3.05±0.05(stat)±0.10(syst) before changing sharply to 5.1±0.3(stat)±0.1(syst) above 5×1019eV.

(4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above 8×1018eV.

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  • Received 20 May 2020
  • Accepted 30 July 2020

DOI:https://doi.org/10.1103/PhysRevD.102.062005

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

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The Anatomy of Ultrahigh-Energy Cosmic Rays

Published 16 September 2020

New results from the Pierre Auger Observatory could narrow down the search for the origin of ultrahigh-energy cosmic rays.

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See Also

Features of the Energy Spectrum of Cosmic Rays above 2.5×1018eV Using the Pierre Auger Observatory

A. Aab et al. (The Pierre Auger Collaboration)
Phys. Rev. Lett. 125, 121106 (2020)

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Vol. 102, Iss. 6 — 15 September 2020

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