Observation of the Suppression of the Flux of Cosmic Rays above 4x10^19 eV

AUGER COLLABORATION, F. SANCHEZ

PHYSICAL REVIEW LETTERS

APS

Año: 2008 p. 611011 - 611017

0031-9007

The energy spectrum of cosmic rays above 2.5 x 10^18 eV, derived from 20000 events recorded at the Pierre Auger Observatory, is described. The spectral index  of the particle flux, J ~ E^-g  , at energies between 4 x10^18 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 Kuzmin.