Measurement of the cosmic ray energy spectrum using hybrid events of the Pierre Auger Observatory

TL;DR

This paper measures the ultra-high energy cosmic ray spectrum using hybrid detection at the Pierre Auger Observatory, providing high-statistics results and detailed systematic uncertainty analysis.

Contribution

It introduces a comprehensive Monte Carlo simulation approach for cross-checking the cosmic ray energy spectrum measurement, enhancing the robustness of the results.

Findings

Identification of the main features of the energy spectrum

Quantification of systematic uncertainties in flux measurements

Updated combined spectrum with surface detector data

Abstract

The energy spectrum of ultra-high energy cosmic rays above 10$^{18}$ eV is measured using the hybrid events collected by the Pierre Auger Observatory between November 2005 and September 2010. The large exposure of the Observatory allows the measurement of the main features of the energy spectrum with high statistics. Full Monte Carlo simulations of the extensive air showers (based on the CORSIKA code) and of the hybrid detector response are adopted here as an independent cross check of the standard analysis (Phys. Lett. B 685, 239 (2010)). The dependence on mass composition and other systematic uncertainties are discussed in detail and, in the full Monte Carlo approach, a region of confidence for flux measurements is defined when all the uncertainties are taken into account. An update is also reported of the energy spectrum obtained by combining the hybrid spectrum and that measured using the surface detector array.