Recent Results on Ultra-High-Energy Cosmic Rays with the Telescope Array Experiment

by Prof. Hiroyuki Sagawa (Institute for Cosmic Ray Research, University of Tokyo)

Tuesday Jun 16, 2026, 3:00 PM → 4:00 PM Pacific/Honolulu

Room 420 (Watanabe Hall)

Ultra-high-energy cosmic rays (UHECRs), which possess extreme energies above 10^18 eV, are believed to originate from powerful astrophysical phenomena in the Universe, yet their exact sources remain an enduring mystery. The primary objective of the Telescope Array (TA) experiment, located in the desert of Utah, USA, is to elucidate the origin of the highest-energy cosmic rays with energies around and above 10^20 eV.  As the largest UHECR observatory in the Northern Hemisphere, the TA experiment covers an area of approximately 700 square kilometers. The observatory employs a hybrid detection technique that combines a large surface detector array with fluorescence telescopes to measure extensive air showers.[1] Furthermore, the inclusion of the Telescope Array Low-energy Extension (TALE) expands the detector's capability, allowing the experiment to cover a wide energy range starting from above 10^15 eV.

Recent observations have provided measurements of the cosmic-ray energy spectrum, revealing characteristic features such as the ankle and the highest-energy cutoff, which are crucial for understanding particle acceleration and propagation mechanisms. In addition, studies of mass composition and arrival-direction anisotropy have provided important insights into possible source candidates and the effects of cosmic magnetic fields. Notably, the detection of an extremely energetic event with an energy of about 2.4 x 10^20 eV has posed new challenges, as no obvious astrophysical source has been identified along its arrival
direction.[2][3]

In this talk, I will review these recent results, including the ongoing TAx4 project focused on the highest energies to expand the aperture fourfold, and discuss the future prospects.

[1] https://urldefense.com/v3/__https://pos.sissa.it/501/1410/__;!!PvDODwlR4mBZyAb0!S_Vht82OOgXZ_2p6P9zDKo0E1S4h6K6XDStpIUNvCGMm0tk7FLSkaQWMfhU2YMN3ugp93YtOtFYcUuuac4rQ4uC6nIM$
[2] https://urldefense.com/v3/__https://www.omu.ac.jp/info/research_news/entry-08954.html__;!!PvDODwlR4mBZyAb0!S_Vht82OOgXZ_2p6P9zDKo0E1S4h6K6XDStpIUNvCGMm0tk7FLSkaQWMfhU2YMN3ugp93YtOtFYcUuuac4rQeMWFSWk$
[3] https://urldefense.com/v3/__https://attheu.utah.edu/facultystaff/cosmic-ray-2023/__;!!PvDODwlR4mBZyAb0!S_Vht82OOgXZ_2p6P9zDKo0E1S4h6K6XDStpIUNvCGMm0tk7FLSkaQWMfhU2YMN3ugp93YtOtFYcUuuac4rQElNtk9w$