Year: 2025
Type: conference-paper
Abstract: The Telescope Array (TA) experiment has been observing extensive air showers (EAS) induced by ultrahigh-energy cosmic rays (UHECR) since 2008. The TA$\times$4 upgrade aims to expand the detection area of TA at the highest energies to four times its original size with 500 additional surface detectors (SD) and with the nearest neighbor spacing extended from 1.2 km to 2.08 km. Half of the new detectors were installed in 2019 and have been operating since then. The objective of the upgrade is to significantly increase the number of events for analysis. In addition to the physical expansion, TA experiment is also investigating improvements of its reconstruction procedure. In particular, TA has previously accepted events only up to a maximum zenith angle of 55 degrees. In this paper, we describe the results of extending the acceptance to 65 degrees in zenith, which required the energy estimation table generated from Monte Carlo simulation (MC) to be expanded to include events up to 70 degrees. To validate the accuracy of MC, which is crucial for both the energy estimation and for the calculation of detector acceptance, we compared distributions of key parameters between observed and simulated TA$\times$4 data. We confirmed that there was no significant discrepancy between the two, in particular for the extended range of zenith angles. We also show the measured TA$\times$4 SD energy spectrum, including events with large zenith angles, based on three years of observations. Finally, we applied the same extension to the TA SD analysis, generating a new energy estimation table for zenith angles up to 70 degrees.
DOI: 10.22323/1.501.0310
Author: Chisato Koyama
Institutions: Institute for Cosmic Ray Research, The University of Tokyo
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Funders: National Science Foundation, University of Utah, European Commission, National Research Foundation, Academia Sinica, National Research Foundation of Korea, University of Tokyo, Forskningsrådet om Hälsa, Arbetsliv och Välfärd, Ministry of Science and Higher Education of the Russian Federation, U.S. Air Force, U.S. Bureau of Land Management, Japan Society for the Promotion of Science, RIKEN, Institute for Cosmic Ray Research, University of Tokyo
Awards: G1192106470, Analysis of Data from the Telescope Array Observatory, Study of the ultra high energy cosmic ray source evolution by detailed measurement of cosmic rays in the wide energy range, Analysis of Data from the Telescope Array Observatory, G2464845396, Quest for the unified picture of the explosion mechanism of supernovae and the central engine of gamma-ray bursts, G2908002831, Investigating the Correlation Between Lightning and High-Energy Particles in the Earth's Atmosphere, G5260365489, G5281852683, Downward Gamma Ray Showers from Natural Lightning, G5629441754, Operation of the Telescope Array Observatory, G6444257319, Exploring energy spectrum anisotropies in ultra-high energy cosmic rays with the Telescope Array, G75659026, Operation of the Telescope Array Observatory, The Microphysics of Lightning: Observing the Optical Emission from Downward Terrestrial Gamma-ray Flashes, Extended Telescope Array Experiment - Nearby Extreme Universe Elucidated by Highest-energy Cosmic Rays, Baseline Support of the University of Utah Cosmic Ray Physics Group Including Analysis of Telescope Array, TALE, and TAx4 Data, Operation of the Telescope Array, TALE, and the TAx4 Expansion by the University of Utah, Extreme Phenomena in the Universe Explored by Highest Energy Cosmic Rays, Study of origins and propagation of very high energy cosmic rays with detailed measurements in the wide energy range
OpenAlex ID: W4414437772
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