The energy spectrum of ultra-high energy cosmic rays measured at the Pierre Auger Observatory and the Telescope Array

¹ University of Utah, High Energy Astrophysics Institute, Salt Lake City, Utah, USA
² CNRS/IN2P3, IJCLab, Université Paris-Saclay, Orsay, France
³ Karlsruhe Institute of Technology (KIT), Institute for Astroparticle Physics, Karlsruhe, Germany
⁴ Graduate School of Science, Osaka Metropolitan University, Osaka, Osaka, Japan
⁵ Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa, Chiba, Japan
⁶ Université Libre de Bruxelles (ULB), Brussels, Belgium
⁷ Karlsruhe Institute of Technology (KIT), Institute for Experimental Particle Physics, Karlsruhe, Germany
⁸ Universitá dell’Aquila, Dipartimento di Scienze Fisiche e Chimiche, L’Aquila, Italy
⁹ INFN Laboratori Nazionali del Gran Sasso, Assergi (L’Aquila), Italy
¹⁰ Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University, Osaka, Osaka, Japan
¹¹ INFN, Sezione di Roma “Tor Vergata”, Roma, Italy
¹² Observatorio Pierre Auger, Av. San Martín Norte 304, 5613 Malargüe, Argentina
¹³ Telescope Array Project, 201 James Fletcher Bldg, 115 S. 1400 East, Salt Lake City, UT 84112-0830, USA

^* Corresponding author: valerio.verzi@roma2.infn.it
^** Corresponding author: spokespersons@auger.org https://www.auger.org/archive/authors_2022_10.html
^*** Corresponding author: http://www.telescopearray.org/research/collaborators

Published online: 28 April 2023

Abstract

In the study of cosmic rays, the measurement of the energy spectrum of the primaries is one of the main issues and provides fundamental information on the most energetic phenomena in the Universe. At ultrahigh energies, beyond 10¹⁸ eV, the cosmic rays are studied by the two largest observatories built so far, the Pierre Auger Observatory and the Telescope Array. Both observatories are based on a hybrid design and reported a measurement of the energy spectrum using the high duty cycle of the surface detector and the calorimetric estimation of the energy scale provided by the fluorescence detector.

The differences among the reported spectra are scrutinized by a working group made by members of the Pierre Auger and Telescope Array Collaborations. The two measurements have been found well in agreement below 10¹⁹ eV while, at higher energies, they show an energy-dependent difference that is beyond the systematic uncertainties associated to the energy scale.

In this contribution we review the status and perspectives of the working group activities including new studies aiming at addressing the impact on the flux measurement at the highest energies of potential biases in the estimation of the shower size.