Measurement of the cosmic-ray energy spectrum above 2.5 × 10 18 eV using the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION, INCLUYE S MOLLERACH

PHYSICAL REVIEW D - PARTICLE AND FILDS

American Physical Society

Año: 2020

0556-2821

We report a measurement of the energy spectrum of cosmic rays for energies above 2.5 × 10 18 eV basedon 215,030 events recorded with zenith angles below 60°. A key feature of the work is that the estimates ofthe energies are independent of assumptions about the unknown hadronic physics or of the primary masscomposition. The measurement is the most precise made hitherto with the accumulated exposure being solarge that the measurements of the flux are dominated by systematic uncertainties except at energies above5 × 10 19 eV. The principal conclusions are(1) The flattening of the spectrum near 5 × 10 18 eV, the so-called ?ankle,? is confirmed.(2) The steepening of the spectrum at around 5 × 10 19 eV is confirmed.(3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index γ of theparticle flux (∝ E −γ ) changes from 2.51 0.03 ðstatÞ 0.05 ðsystÞ to 3.05 0.05 ðstatÞ 0.10 ðsystÞbefore changing sharply to 5.1 0.3 ðstatÞ 0.1 ðsystÞ above 5 × 10 19 eV.(4) No evidence for any dependence of the spectrum on declination has been found other than a mildexcess from the Southern Hemisphere that is consistent with the anisotropy observed above8 × 10 18 eV.