# Measurement of the cosmic-ray energy spectrum above 2.5 x 10(18) eV using the Pierre Auger Observatory

Pierre Auger Collaboration; Aab, A.; Abreu, P.; Aglietta, M.; Albury, J. M.; Allekotte, I.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Alves Batista, R.; Anastasi, G. A.; Anchordoqui, L.; Andrada, B.; Andringa, S.; Aramo, C.; Araújo Ferreira, P. R.; Asorey, H.; Assis, P.; Avila, G.; Badescu, A. M.; Bakalova, A.; ... mehr

##### Abstract:
We report a measurement of the energy spectrum of cosmic rays for energies above 2.5×10$^{18}$ eV 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 5×10$^{19}$ eV. The principal conclusions are

(1) The flattening of the spectrum near 5×10$^{18}$ eV, the so-called “ankle,” is confirmed.

(2) The steepening of the spectrum at around 5×10$^{Z19}$ eV 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 (∝E$^{−γ }$) 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 5×10$^{19}$ eV.

(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 8×10$^{18}$ eV.

 Zugehörige Institution(en) am KIT Institut für Experimentelle Teilchenphysik (ETP)Institut für Kernphysik (IKP)Institut für Prozessdatenverarbeitung und Elektronik (IPE) Publikationstyp Zeitschriftenaufsatz Publikationsjahr 2020 Sprache Englisch Identifikator ISSN: 2470-0010, 2470-0029 KITopen-ID: 1000125498 HGF-Programm 51.03.03 (POF III, LK 01) Kosmische Strahlung Auger Erschienen in Physical review / D Verlag American Physical Society (APS) Band 102 Heft 6 Seiten Art. Nr.: 062005 Vorab online veröffentlicht am 16.09.2020 Nachgewiesen in Web of ScienceDimensions
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