Observation of the suppression of the flux of cosmic rays above 4×1019eV

Authors

J. Abraham, Universidad Tecnologica Nacional
P. Abreu, Instituto Superior Técnico
M. Aglietta, Università degli Studi di Torino
C. Aguirre, Universidad Catolica de Bolivia
D. Allard, APC - AstroParticule et Cosmologie
I. Allekotte, Centro Atomico Bariloche
J. Allen, New York University
P. Allison, The Ohio State University
J. Alvarez-Muñiz, Universidad de Santiago de Compostela
M. Ambrosio, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
L. Anchordoqui, University of Wisconsin-Milwaukee
S. Andringa, Instituto Superior Técnico
A. Anzalone, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica di Palermo
C. Aramo, Istituto Nazionale di Fisica Nucleare, Sezione di Napoli
S. Argirò, Università degli Studi di Torino
K. Arisaka, University of California, Los Angeles
E. Armengaud, APC - AstroParticule et Cosmologie
F. Arneodo, Laboratori Nazionali del Gran Sasso
F. Arqueros, Universidad Complutense de Madrid
T. Asch, Karlsruhe Institute of Technology, Campus North
H. Asorey, Centro Atomico Bariloche
P. Assis, Instituto Superior Técnico
B. S. Atulugama, Pennsylvania State University
J. Aublin, Laboratoire de Physique Nucléaire et de Hautes Energies
M. Ave, The Enrico Fermi Institute
G. Avila, Comision Nacional de Energia Atomica Argentina
T. Bäcker, Universität Siegen
D. Badagnani, Universidad Nacional de La Plata
A. F. Barbosa, Centro Brasileiro de Pesquisas Físicas
D. Barnhill, University of California, Los Angeles
S. L.C. Barroso, Universidade Estadual do Sudoeste da Bahia
B. Baughman, The Ohio State University

Document Type

Article

Publication Date

8-4-2008

Abstract

The energy spectrum of cosmic rays above 2.5×1018eV, derived from 20000 events recorded at the Pierre Auger Observatory, is described. The spectral index γ of the particle flux, JE-γ, at energies between 4×1018eV and 4×1019eV is 2.69±0.02(stat)±0.06(syst), steepening to 4.2±0.4(stat)±0.06(syst) at higher energies. The hypothesis of a single power law is rejected with a significance greater than 6 standard deviations. The data are consistent with the prediction by Greisen and by Zatsepin and Kuz'min. © 2008 The American Physical Society.

Publication Title

Physical Review Letters

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