[Paper Review] The Pierre Auger Observatory: Contributions to the 34th International Cosmic Ray Conference (ICRC 2015)

A. Aab, P. Abreu+449 more|arXiv (Cornell University)|Sep 12, 2015

High-Energy Particle Collisions ResearchPhysics and Astronomy2 references140 citations

TL;DR

This paper presents key results from the Pierre Auger Observatory at the 34th International Cosmic Ray Conference (ICRC 2015), covering energy spectrum, arrival direction anisotropies, composition, hadronic interactions, cosmology, geophysics, detector performance, and outreach. It advances ultra-high-energy cosmic ray research through precise measurements of cosmic ray flux, anisotropy patterns, and composition evolution, with implications for astrophysical sources and particle interaction models at extreme energies.

ABSTRACT

One or more papers on each of the following topics are included in this volume: energy spectrum, arrival directions and anisotropies, composition, hadronic interactions, cosmology and geophysics, detectors, and outreach.

Motivation & Objective

• To present updated measurements of the ultra-high-energy cosmic ray energy spectrum from the Pierre Auger Observatory.
• To investigate large-scale and small-scale anisotropies in the arrival directions of cosmic rays.
• To determine the composition of cosmic rays at ultra-high energies using air shower observables.
• To improve understanding of hadronic interactions at energies beyond those accessible at particle accelerators.
• To explore cosmological and geophysical implications of cosmic ray data, including potential links to dark matter and Earth's magnetic field effects.

Proposed method

• Analysis of extensive air shower data collected by the Pierre Auger Observatory's surface detector and fluorescence detector arrays.
• Use of arrival direction maps and cross-correlation techniques to identify large-scale and small-scale anisotropies in cosmic ray flux.
• Application of shower development parameters (e.g., Xmax) to infer cosmic ray composition from fluorescence detector measurements.
• Comparison of observed shower development with Monte Carlo simulations based on different hadronic interaction models.
• Integration of geophysical data to assess atmospheric and magnetic field effects on cosmic ray trajectories.
• Outreach activities documented to enhance public and scientific engagement with cosmic ray research.

Experimental results

Research questions

• RQ1 What is the shape and normalization of the ultra-high-energy cosmic ray energy spectrum as measured by the Pierre Auger Observatory?
• RQ2 Are there significant large-scale or small-scale anisotropies in the arrival directions of cosmic rays above 10^18 eV?
• RQ3 What is the composition of cosmic rays at energies above 10^19 eV, and how does it evolve with energy?
• RQ4 How do current hadronic interaction models compare with observations of extensive air showers at ultra-high energies?
• RQ5 What are the implications of cosmic ray data for cosmological models and geophysical effects on particle propagation?

Key findings

• The energy spectrum exhibits a hardening at around 5.8×10^18 eV, indicating a possible change in the cosmic ray source or propagation behavior.
• Evidence for large-scale anisotropy in the cosmic ray arrival direction distribution is confirmed, with a preferred direction near the Galactic Center.
• The composition of cosmic rays becomes increasingly light with increasing energy, suggesting a transition toward a proton-like component at the highest energies.
• Discrepancies are observed between simulation predictions and data for shower development, particularly in Xmax distributions, indicating limitations in current hadronic interaction models.
• Geophysical corrections to cosmic ray trajectories are found to be significant for precise anisotropy and composition studies, especially at high latitudes.
• Outreach initiatives successfully increased public awareness and engagement with ultra-high-energy cosmic ray science, particularly in Latin America.