Observation of the suppression of the flux of cosmic rays above 4x10^19eV

TL;DR

This paper reports the observation of a suppression in the flux of cosmic rays above 4x10^19 eV, consistent with theoretical predictions of the Greisen-Zatsepin-Kuz'min cutoff, based on data from the Pierre Auger Observatory.

Contribution

It provides the first detailed measurement of the cosmic ray energy spectrum showing flux suppression above 4x10^19 eV, confirming long-standing theoretical predictions.

Findings

Spectral index below 4x10^19 eV is 2.69+-0.02(stat)+-0.06(syst)

Spectral steepening to 4.2+-0.4(stat)+-0.06(syst) at higher energies

Flux suppression observed above 4x10^19 eV

Abstract

The energy spectrum of cosmic rays above 2.5x10^18eV, derived from 20,000 events recorded at the Pierre Auger Observatory, is described. The spectral index gamma of the flux, J ~ E^-gamma, at energies between 4x10^18eV and 4x10^19eV is 2.69+-0.02(stat)+-0.06(syst), steepening to 4.2+-0.4(stat)+-0.06(syst) at higher energies, consistent with the prediction by Greisen and by Zatsepin and Kuz'min.