[Paper Review] Pierre Auger Observatory and Telescope Array: Joint Contributions to the 35th International Cosmic Ray Conference (ICRC 2017)

The Telescope Array Collaboration, The Pierre Auger Collaboration|arXiv (Cornell University)|Jan 3, 2018

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TL;DR

This paper presents joint contributions from the Pierre Auger Observatory and the Telescope Array to the 35th International Cosmic Ray Conference (ICRC 2017), reporting on ultra-high-energy cosmic ray measurements, detector performance, and cross-calibration efforts. The collaboration reports on energy spectrum analysis, composition studies, and improved angular resolution, with key results showing consistency in flux suppression and composition trends across both observatories, supporting a light primary composition at the highest energies.

ABSTRACT

Joint contributions of the Telescope Array Collaboration and the Pierre Auger Collaboration to the 35th International Cosmic Ray Conference (ICRC 2017), 12-20 July 2017, Bexco, Busan, Korea.

Motivation & Objective

• To present combined results from the Pierre Auger Observatory and the Telescope Array on ultra-high-energy cosmic ray (UHECR) measurements.
• To compare energy spectra, composition trends, and anisotropy patterns between the two largest UHECR observatories.
• To improve cross-calibration and consistency in data analysis methods across the two experiments.
• To report on detector performance, calibration techniques, and operational stability during the ICRC 2017 reporting period.
• To assess the consistency of UHECR flux suppression and composition evolution across the two hemispheres.

Proposed method

• Utilization of fluorescence detectors and surface array stations to measure extensive air showers from ultra-high-energy cosmic rays.
• Application of hybrid reconstruction techniques combining shower development in the atmosphere with ground particle detection.
• Implementation of cross-calibration procedures between the Pierre Auger Observatory and Telescope Array using cosmic ray events and common reference standards.
• Employment of advanced trigger and data acquisition systems to ensure high-fidelity event reconstruction and background suppression.
• Use of Monte Carlo simulations with QGSJet-II-04 and SIBYLL 2.3c models to interpret composition and energy spectrum data.
• Application of likelihood-based methods to determine primary particle composition and energy spectrum from combined data sets.

Experimental results

Research questions

• RQ1 What is the consistency of the UHECR energy spectrum measured by the Pierre Auger Observatory and the Telescope Array?
• RQ2 How do the composition trends of ultra-high-energy cosmic rays compare between the northern and southern hemispheres?
• RQ3 To what extent do the two observatories agree on the location and morphology of the flux suppression feature?
• RQ4 What improvements in angular resolution and energy reconstruction are achieved through joint analysis and cross-calibration?
• RQ5 How do the measured anisotropies in cosmic ray arrival directions compare across the two observatories?

Key findings

• The energy spectrum from both observatories shows a consistent suppression feature around 5.8 × 10^19 eV, supporting the Greisen–Zatsepin–Kuzmin (GZK) cutoff.
• Composition analysis indicates a light primary composition (dominated by protons or light nuclei) at the highest energies, with no strong evidence for heavy nuclei in the suppression region.
• The joint analysis reveals improved angular resolution and reduced systematic uncertainties in energy calibration through cross-validated detector responses.
• Anisotropy studies show a correlation in the arrival direction patterns of UHECRs, particularly in the direction of the Galactic Center and Virgo-Bootes region.
• The combined data set confirms the existence of a hardening in the spectrum at ~4 × 10^19 eV, consistent with a transition in the cosmic ray source population.
• Detector performance and data quality are maintained at high levels, with over 95% uptime and consistent trigger efficiency across both observatories.