Observation of the Suppression of the Flux of Cosmic Rays above 4 x 10^19 eV

PIERRE AUGER COLLABORATION: SON 458 AUTORES. A. PICHEL

PHYSICAL REVIEW LETTERS

AMER PHYSICAL SOC

Año: 2008 vol. 101 p. 61101 - 61101

0031-9007

The energy spectrum of cosmic rays above 2.5 x 10^18 eV, derived from 20.000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the particle flux, J ~ E^-gamma, at energies between 4 x 10^18 eV and 4 x 10^19 eV 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.