The performance of the TA$times$4 surface detector array: 4.3 years of the first-half expansion

The performance of the TA$times$4 surface detector array: 4.3 years of the first-half expansion
Telescope Array Collaboration, R. U. Abbasi (Department of Physics, Loyola University-Chicago, Chicago, Illinois 60660, USA), T. Abu-Zayyad (Department of Physics, Loyola University-Chicago, Chicago, Illinois 60660, USA, High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), M. Allen (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), J. W. Belz (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), D. R. Bergman (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), F. Bradfield (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), I. Buckland (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), W. Campbell (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), B. G. Cheon (Department of Physics and The Research Institute of Natural Science, Hanyang University, Seongdong-gu, Seoul 426-791, Korea), K. Endo (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), A. Fedynitch (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan, Institute of Physics, Academia Sinica, Taipei City 115201, Taiwan), T. Fujii (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan, Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), K. Fujisue (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan, Institute of Physics, Academia Sinica, Taipei City 115201, Taiwan), K. Fujita (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), M. Fukushima (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), G. Furlich (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), A. G’alvez Ure~na (CEICO, Institute of Physics, Czech Academy of Sciences, Prague 182 21, Czech Republic), Z. Gerber (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), N. Globus (Institute of Astronomy, National Autonomous University of Mexico Ensenada Campus, Ensenada, BC 22860, Mexico), T. Hanaoka (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), W. Hanlon (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), N. Hayashida (Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan), H. He (Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama 351-0198, Japan), K. Hibino (Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan), R. Higuchi (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan, Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama 351-0198, Japan), D. Ikeda (Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan), D. Ivanov (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), S. Jeong (Department of Physics, Sungkyunkwan University, Jang-an-gu, Suwon 16419, Korea), C. C. H. Jui (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), K. Kadota (Department of Physics, Tokyo City University, Setagaya-ku, Tokyo 158-8557, Japan), F. Kakimoto (Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan), O. Kalashev (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), K. Kasahara (Faculty of Systems Engineering and Science, Shibaura Institute of Technology, Minumaku, Tokyo 337-8570, Japan), Y. Kawachi (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), K. Kawata (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), I. Kharuk (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), E. Kido (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan, Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama 351-0198, Japan), H. B. Kim (Department of Physics and The Research Institute of Natural Science, Hanyang University, Seongdong-gu, Seoul 426-791, Korea), J. H. Kim (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), J. H. Kim (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), S. W. Kim (Department of Physics, Sungkyunkwan University, Jang-an-gu, Suwon 16419, Korea), R. Kobo (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), I. Komae (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), K. Komatsu (Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan), K. Komori (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), A. Korochkin (Service de Physique Th’eorique, Universit’e Libre de Bruxelles, Brussels 1050, Belgium), C. Koyama (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), M. Kudenko (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), M. Kuroiwa (Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan), Y. Kusumori (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), M. Kuznetsov (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), Y. J. Kwon (Department of Physics, Yonsei University, Seodaemun-gu, Seoul 120-749, Korea), K. H. Lee (Department of Physics and The Research Institute of Natural Science, Hanyang University, Seongdong-gu, Seoul 426-791, Korea), M. J. Lee (Department of Physics, Sungkyunkwan University, Jang-an-gu, Suwon 16419, Korea), B. Lubsandorzhiev (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), J. P. Lundquist (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA, Center for Astrophysics and Cosmology, University of Nova Gorica, Nova Gorica 5297, Slovenia), H. Matsushita (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), A. Matsuzawa (Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan), J. A. Matthews (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), J. N. Matthews (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), K. Mizuno (Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan), M. Mori (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), S. Nagataki (Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama 351-0198, Japan), K. Nakagawa (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), M. Nakahara (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), H. Nakamura (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), T. Nakamura (Faculty of Science, Kochi University, Kochi, Kochi 780-8520, Japan), T. Nakayama (Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan), Y. Nakayama (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), K. Nakazawa (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), T. Nonaka (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), S. Ogio (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), H. Ohoka (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), N. Okazaki (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), M. Onishi (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), A. Oshima (College of Science and Engineering, Chubu University, Kasugai, Aichi 487-8501, Japan), H. Oshima (School of Science and Engineering, Tokyo Denki University, Saitama, 350-0394, Japan), S. Ozawa (Quantum ICT Advanced Development Center, National Institute for Information and Communications Technology, Koganei, Tokyo 184-8795, Japan), I. H. Park (Department of Physics, Sungkyunkwan University, Jang-an-gu, Suwon 16419, Korea), K. Y. Park (Department of Physics and The Research Institute of Natural Science, Hanyang University, Seongdong-gu, Seoul 426-791, Korea), M. Potts (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), M. Przybylak (Doctoral School of Exact and Natural Sciences, University of Lodz, Lodz, Lodz 90-237, Poland), M. S. Pshirkov (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia, Sternberg Astronomical Institute, Moscow M.V. Lomonosov State University, Moscow 119991, Russia), J. Remington (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), C. Rott (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), G. I. Rubtsov (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), D. Ryu (Department of Physics, School of Natural Sciences, Ulsan National Institute of Science and Technology, UNIST-gil, Ulsan 689-798, Korea), H. Sagawa (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), N. Sakaki (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), R. Sakamoto (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), T. Sako (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), N. Sakurai (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), S. Sakurai (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), D. Sato (Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan), K. Sekino (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), T. Shibata (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), J. Shikita (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), H. Shimodaira (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), H. S. Shin (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan, Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), K. Shinozaki (Astrophysics Division, National Centre for Nuclear Research, Warsaw 02-093, Poland), J. D. Smith (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), P. Sokolsky (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), B. T. Stokes (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), T. A. Stroman (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), H. Tachibana (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), K. Takahashi (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), M. Takeda (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), R. Takeishi (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), A. Taketa (Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo 277-8582, Japan), M. Takita (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan), Y. Tameda (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), K. Tanaka (Graduate School of Information Sciences, Hiroshima City University, Hiroshima, Hiroshima 731-3194, Japan), M. Tanaka (Institute of Particle and Nuclear Studies, KEK, Tsukuba, Ibaraki 305-0801, Japan), M. Teramoto (Graduate School of Engineering, Osaka Electro-Communication University, Neyagawa-shi, Osaka 572-8530, Japan), S. B. Thomas (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), G. B. Thomson (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), P. Tinyakov (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia, Service de Physique Th’eorique, Universit’e Libre de Bruxelles, Brussels 1050, Belgium), I. Tkachev (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), T. Tomida (Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan), S. Troitsky (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), Y. Tsunesada (Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan, Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan), S. Udo (Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan), F. R. Urban (CEICO, Institute of Physics, Czech Academy of Sciences, Prague 182 21, Czech Republic), M. Vr’abel (Astrophysics Division, National Centre for Nuclear Research, Warsaw 02-093, Poland), D. Warren (Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama 351-0198, Japan), K. Yamazaki (College of Science and Engineering, Chubu University, Kasugai, Aichi 487-8501, Japan), Y. Zhezher (Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan, Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia), Z. Zundel (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA), J. Zvirzdin (High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA)
arXiv:2606.28051v2 Announce Type: replace
Abstract: The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arrival directions of cosmic-ray events with energy greater than 57 EeV. To improve the exposure for anisotropy studies of UHECRs, the TA$times$4 upgrade was designed to expand the observational area by approximately 2,000 km$^2$ with 500 additional SDs. Half of the planned upgrade, consisting of 257 SDs, was completed, and the newly installed array began operation in 2019. In addition to the expanded SD array, two FD stations were constructed for the TA$times$4 experiment. In this paper, we present a study of the performance of the expanded SD array, including the energy resolution, angular resolution, and effective aperture, over the first 4.3 years of data acquisition. While the effective aperture varied initially due to changing detector states, it has stabilized since June 2023 with more than 90% operational SDs. Furthermore, a new inter-tower trigger system was implemented to connect six new communication towers to form two geographically separated arrays, increasing the effective aperture. The time variation of this effective aperture, the resulting total exposure of approximately 3,500 km$^2$ sr yr, and a comparison with the original TA SD array are presented to demonstrate the performance of the expanded array.arXiv:2606.28051v2 Announce Type: replace
Abstract: The Telescope Array (TA) experiment aims to reveal the origin of ultra-high-energy cosmic rays (UHECRs) by observing air showers using surface detectors (SDs), which spread over an area of approximately 700 km$^2$, and fluorescence detectors (FDs) viewing the skies above the SD array. The TA experiment has been observing UHECRs since 2008, and has reported an indication of clustering in the arrival directions of cosmic-ray events with energy greater than 57 EeV. To improve the exposure for anisotropy studies of UHECRs, the TA$times$4 upgrade was designed to expand the observational area by approximately 2,000 km$^2$ with 500 additional SDs. Half of the planned upgrade, consisting of 257 SDs, was completed, and the newly installed array began operation in 2019. In addition to the expanded SD array, two FD stations were constructed for the TA$times$4 experiment. In this paper, we present a study of the performance of the expanded SD array, including the energy resolution, angular resolution, and effective aperture, over the first 4.3 years of data acquisition. While the effective aperture varied initially due to changing detector states, it has stabilized since June 2023 with more than 90% operational SDs. Furthermore, a new inter-tower trigger system was implemented to connect six new communication towers to form two geographically separated arrays, increasing the effective aperture. The time variation of this effective aperture, the resulting total exposure of approximately 3,500 km$^2$ sr yr, and a comparison with the original TA SD array are presented to demonstrate the performance of the expanded array.