Measurement of the cosmic ray spectrum above 4 × 10¹⁸eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding 4×10<sup>18</sup> eV is presented, which is based on the analysis of showers with zenith angles greater than 60° detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above 5.3×10<sup>18</sup> eV, the ``ankle'', the flux can be described by a power law E<sup>–γ</sup> with index γ=2.70 ± 0.02 (stat) ± 0.1 (sys) followed by a smooth suppression region. For the energy (E<sub>s</sub>) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find E<sub>s</sub>=(5.12±0.25 (stat)<sup>+1.0</sup><sub>–1.2</sub> (sys))×10<sup>19</sup> eV.

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