Measurement of the cosmic ray spectrum above \(4{\times}10^{18}\) eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding \(4{\times}10^{18}\) eV is presented, which is based on the analysis of showers with zenith angles greater than \(60^{\circ}\) 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 \(5.3{\times}10^{18}\) eV, the "ankle", the flux can be described by a power law \(E^{-\gamma}\) with index \(\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}\) followed by a smooth suppression region. For the energy (\(E_\text{s}\)) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find \(E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}\) eV.