Energy spectrum and mass composition of cosmic rays from Phase I data measured using the Pierre Auger Observatory

TL;DR

This paper presents the most precise measurements to date of the energy spectrum and mass composition of ultra-high energy cosmic rays using data from the Pierre Auger Observatory's first operational phase, covering energies from 6 PeV to over 1 EeV.

Contribution

It provides new, high-precision estimates of the cosmic ray energy spectrum and mass composition across a wide energy range, utilizing both fluorescence and surface detector data from the Pierre Auger Observatory.

Findings

Most precise energy spectrum measurements to date.

Consistent mass composition analysis from multiple detection methods.

Extended measurements down to 6 PeV for comprehensive coverage.

Abstract

The Pierre Auger Observatory concluded its first phase of data taking after seventeen years of operation. The dataset collected by its surface and fluorescence detectors (FD and SD) provides us with the most precise estimates of the energy spectrum and mass composition of ultra-high energy cosmic rays yet available. We present measurements of the depth of shower maximum, the main quantity used to derive species of primary particles, determined either from the direct observation of longitudinal profiles of showers by the FD, or indirectly through the analysis of signals in the SD stations. The energy spectrum of primaries is also determined from both FD and SD measurements, where the former exhibits lower systematic uncertainty in the energy determination while the latter exploits unprecedentedly large exposure. The data for primaries with energy below 1 EeV are also available thanks to the high-elevation telescopes of FD and the denser array of SD, making measurements possible down to 6 PeV and 60 PeV, respectively.