Testing the Compatibility of the Depth of the Shower Maximum Measurements performed at Telescope Array and the Pierre Auger Observatory

Auger-TA Mass Composition Working Group Report

¹ University of Utah, High Energy Astrophysics Institute, Salt Lake City, UT, USA
² University of Adelaide, Adelaide, S.A., Australia
³ Universidade de São Paulo, Instituto de Física de São Carlos, São Carlos, SP, Brazil
⁴ Karlsruhe Institute of Technology, Institute for Astroparticle Physics, Karlsruhe, Germany
⁵ Colorado School of Mines, Golden, CO, USA
⁶ Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic
⁷ Telescope Array Project, 201 James Fletcher Bldg, 115 S 1400 East, Salt Lake City, UT 84112-0830, USA Full author list: http://www.telescopearray.org/research/collaborators
⁸ Observatorio Pierre Auger, Av. San Martín Norte 304, 5613, Malargüe, Argentina. Full author list: http://www.auger.org/archive/authors_2022_10.html

^* Corresponding author: bergman@physics.utah.edu
^** Corresponding author: auger_spokespersons@fnal.gov

Published online: 28 April 2023

Abstract

The Telescope Array and the Pierre Auger Observatory estimate the composition of ultra-high-energy cosmic rays by observing the distribution of depths of air-shower maxima, X _max. Both experiments directly observe the longitudinal development of air showers using fluorescence telescopes with surface particle detectors used in conjunction to provide precision in determining air-shower geometry. The two experiments differ in the details of the analysis of events, so a direct comparison of X _max distributions is not possible. The Auger – Telescope Array Composition Working Group presents their results from a technique to compare X _max measurements from Auger with those of Telescope Array. In particular, the compatibility of the first two moments of the X _max distributions of Auger with the data from the Black Rock Mesa and Long Ridge detectors of the Telescope Array is tested for energies above 10^18.2 eV. Quantitative comparisons are obtained using air-shower simulations of four representative species made using the Sibyll 2.3d high-energy interaction model. These are weighted to fit the fractional composition seen in Auger data and reconstructed using the Telescope Array detector response and analysis methods.