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    Mass composition of ultrahigh energy cosmic rays from distribution of their arrival directions with the Telescope Array

    R. U. Abbasi1, Y. Abe2, T. Abu-Zayyad1,3, M. Allen3, Y. Arai4, R. Arimura4, E. Barcikowski3, J. W. Belz3, D. R. Bergman3 et al. (Telescope Array Collaboration)

    D. R. Bergman3, S. A. Blake3, I. Buckland3, B. G. Cheon5, M. Chikawa6, T. Fujii4,31, K. Fujisue6,7, K. Fujita6, R. Fujiwara4, M. Fukushima6, G. Furlich3, N. Globus8,†, R. Gonzalez3, W. Hanlon3, N. Hayashida9, H. He8,¶, R. Hibi2, K. Hibino9, R. Higuchi8, K. Honda10, D. Ikeda9, N. Inoue11, T. Ishii10, H. Ito8, D. Ivanov3, A. Iwasaki4, H. M. Jeong12, S. Jeong12, C. C. H. Jui3, K. Kadota13, F. Kakimoto9, O. Kalashev14, K. Kasahara15, S. Kasami16, S. Kawakami4, K. Kawata6, I. Kharuk14, E. Kido8, H. B. Kim5, J. H. Kim3,‡, J. H. Kim3, S. W. Kim12,**, Y. Kimura4, I. Komae4, V. Kuzmin14,*, M. Kuznetsov17,14,§, Y. J. Kwon18, K. H. Lee12, B. Lubsandorzhiev14, J. P. Lundquist19,3, H. Matsumiya4, T. Matsuyama4, J. N. Matthews3, R. Mayta4, K. Mizuno2, M. Murakami16, I. Myers3, K. H. Lee5, S. Nagataki8, K. Nakai4, T. Nakamura20, E. Nishio16, T. Nonaka6, H. Oda4, S. Ogio6, M. Onishi6, H. Ohoka6, N. Okazaki6, Y. Oku16, T. Okuda21, Y. Omura4, M. Ono8, A. Oshima22, H. Oshima6, S. Ozawa23, I. H. Park12, K. Y. Park5, M. Potts3, M. S. Pshirkov14,24, J. Remington3,††, D. C. Rodriguez3, C. Rott3,12, G. I. Rubtsov14, D. Ryu25, H. Sagawa6, R. Saito2, N. Sakaki6, T. Sako6, N. Sakurai4, D. Sato2, K. Sato4, S. Sato16, K. Sekino6, P. D. Shah3, N. Shibata16, T. Shibata6, J. Shikita4, H. Shimodaira6, B. K. Shin25, H. S. Shin4,31, D. Shinto16, J. D. Smith3, P. Sokolsky3, B. T. Stokes3, T. A. Stroman3, Y. Takagi16, K. Takahashi6, M. Takamura26, M. Takeda6, R. Takeishi6, A. Taketa27, M. Takita6, Y. Tameda16, K. Tanaka28, M. Tanaka29, Y. Tanoue4, S. B. Thomas3, G. B. Thomson3, P. Tinyakov17,14,∥, I. Tkachev14, H. Tokuno30, T. Tomida2, S. Troitsky14, R. Tsuda4, Y. Tsunesada4,31, S. Udo9, F. Urban32, D. Warren8, T. Wong3, K. Yamazaki22, K. Yashiro26, F. Yoshida16, Y. Zhezher6,14, and Z. Zundel3 (Telescope Array Collaboration)

    • 1Department of Physics, Loyola University Chicago, Chicago, Illinois 60660, USA
    • 2Academic Assembly School of Science and Technology Institute of Engineering, Shinshu University, Nagano, Nagano 380-8554, Japan
    • 3High Energy Astrophysics Institute and Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112-0830, USA
    • 4Graduate School of Science, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan
    • 5Department of Physics and The Research Institute of Natural Science, Hanyang University, Seongdong-gu, Seoul 426-791, Korea
    • 6Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan
    • 7Institute of Physics, Academia Sinica, Taipei City 115201, Taiwan
    • 8Astrophysical Big Bang Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
    • 9Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan
    • 10Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Kofu, Yamanashi 400-8511, Japan
    • 11The Graduate School of Science and Engineering, Saitama University, Saitama, Saitama 338-8570, Japan
    • 12Department of Physics, SungKyunKwan University, Jang-an-gu, Suwon 16419, Korea
    • 13Department of Physics, Tokyo City University, Setagaya-ku, Tokyo 158-8557, Japan
    • 14Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 117312, Russia
    • 15Faculty of Systems Engineering and Science, Shibaura Institute of Technology, Minato-ku, Tokyo 337-8570, Japan
    • 16Graduate School of Engineering, Osaka Electro-Communication University, Hatsu-cho, Neyagawa-shi, Osaka 572-8530, Japan
    • 17Service de Physique Théorique, Université Libre de Bruxelles, Brussels 1050, Belgium
    • 18Department of Physics, Yonsei University, Seodaemun-gu, Seoul 120-749, Korea
    • 19Center for Astrophysics and Cosmology, University of Nova Gorica, Nova Gorica 5297, Slovenia
    • 20Faculty of Science, Kochi University, Kochi, Kochi 780-8520, Japan
    • 21Department of Physical Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
    • 22College of Engineering, Chubu University, Kasugai, Aichi 487-8501, Japan
    • 23Quantum ICT Advanced Development Center, National Institute for Information and Communications Technology, Koganei, Tokyo 184-8795, Japan
    • 24Sternberg Astronomical Institute, Moscow M.V. Lomonosov State University, Moscow 119991, Russia
    • 25Department of Physics, School of Natural Sciences, Ulsan National Institute of Science and Technology, UNIST-gil, Ulsan 689-798, Korea
    • 26Department of Physics, Tokyo University of Science, Noda, Chiba 162-8601, Japan
    • 27Earthquake Research Institute, University of Tokyo, Bunkyo-ku, Tokyo 277-8582, Japan
    • 28Graduate School of Information Sciences, Hiroshima City University, Hiroshima, Hiroshima 731-3194, Japan
    • 29Institute of Particle and Nuclear Studies, KEK, Tsukuba, Ibaraki 305-0801, Japan
    • 30Graduate School of Science and Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan
    • 31Nambu Yoichiro Institute of Theoretical and Experimental Physics, Osaka Metropolitan University, Sugimoto, Sumiyoshi, Osaka 558-8585, Japan
    • 32CEICO, Institute of Physics, Czech Academy of Sciences, Prague 182 21, Czech Republic

    • *Deceased.
    • †Present address: KIPAC, Stanford University, Stanford, California 94305, USA.
    • ‡Present address: Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
    • §mkuzn@inr.ac.ru
    • ∥petr.tiniakov@ulb.be
    • Present address: Purple Mountain Observatory, Nanjing 210023, China.
    • **Present address: Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea.
    • ††Present address: NASA Marshall Space Flight Center, Huntsville, Alabama 35812, USA.

    Phys. Rev. D 110, 022006 – Published 22 July, 2024

    DOI: https://doi.org/10.1103/PhysRevD.110.022006

    Abstract

    We use a new method to estimate the injected mass composition of ultrahigh cosmic rays (UHECRs) at energies higher than 10 EeV. The method is based on comparison of the energy-dependent distribution of cosmic ray arrival directions as measured by the Telescope Array (TA) experiment with that calculated in a given putative model of UHECR under the assumption that sources trace the large-scale structure (LSS) of the Universe. As we report in the companion Letter, the TA data show large deflections with respect to the LSS which can be explained, assuming small extragalactic magnetic fields (EGMF), by an intermediate composition changing to a heavy one (iron) in the highest energy bin. Here we show that these results are robust to uncertainties in UHECR injection spectra, the energy scale of the experiment and galactic magnetic fields. The assumption of weak EGMF, however, strongly affects this interpretation at all but the highest energies E>100  EeV, where the remarkable isotropy of the data implies a heavy injected composition even in the case of strong EGMF. This result also holds if UHECR sources are as rare as 2×10−5  Mpc−3, that is the conservative lower limit for the source number density.

    Physics Subject Headings (PhySH)

    See Also

    Isotropy of Cosmic Rays beyond 1020  eV Favors Their Heavy Mass Composition

    R. U. Abbasi et al. (Telescope Array Collaboration)
    Phys. Rev. Lett. 133, 041001 (2024)

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