Observation of the Suppression of the Flux of Cosmic Rays above 4 × 1019 eV.

J. ABRAHAM,...; X. BERTOU

PHYSICAL REVIEW LETTERS

AMER PHYSICAL SOC

Año: 2008 vol. 101 p. 1 - 7

0031-9007

The energy spectrum of cosmic rays above 2:5 􏰀 1018 eV, derived from 20 000 events recorded at the Pierre Auger Observatory, is described. The spectral index 􏰋 of the particle flux, J / E􏰁􏰋, at energies between 4 􏰀 1018 eV and 4 􏰀 1019 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.