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arXiv · 2603.14804

Cosmic ray mass composition measurement in the energy range from $10^{16.5}$ eV to $10^{18.5}$ eV observed with the TALE hybrid detector

Telescope Array Collaboration·R. U. Abbasi·T. Abu-Zayyad·M. Allen·J. W. Belz·D. R. Bergman·F. Bradfield·I. Buckland·W. Campbell·B. G. Cheon·K. Endo·A. Fedynitch·T. Fujii·K. Fujisue·K. Fujita·M. Fukushima·G. Furlich·A. Gálvez Ureña·Z. Gerber·N. Globus·T. Hanaoka·W. Hanlon·N. Hayashida·H. He·K. Hibino·R. Higuchi·D. Ikeda·D. Ivanov·S. Jeong·C. C. H. Jui·K. Kadota·F. Kakimoto·O. Kalashev·K. Kasahara·Y. Kawachi·K. Kawata·I. Kharuk·E. Kido·H. B. Kim·J. H. Kim·S. W. Kim·R. Kobo·I. Komae·K. Komatsu·K. Komori·A. Korochkin·C. Koyama·M. Kudenko·M. Kuroiwa·Y. Kusumori·M. Kuznetsov·Y. J. Kwon·K. H. Lee·M. J. Lee·B. Lubsandorzhiev·J. P. Lundquist·H. Matsushita·A. Matsuzawa·J. A. Matthews·J. N. Matthews·K. Mizuno·M. Mori·S. Nagataki·K. Nakagawa·M. Nakahara·H. Nakamura·T. Nakamura·T. Nakayama·Y. Nakayama·K. Nakazawa·T. Nonaka·S. Ogio·H. Ohoka·N. Okazaki·M. Onishi·A. Oshima·H. Oshima·S. Ozawa·I. H. Park·K. Y. Park·M. Potts·M. Przybylak·M. S. Pshirkov·J. Remington·C. Rott·G. I. Rubtsov·D. Ryu·H. Sagawa·N. Sakaki·R. Sakamoto·T. Sako·N. Sakurai·S. Sakurai·D. Sato·K. Sekino·T. Shibata·J. Shikita·H. Shimodaira·H. S. Shin·K. Shinozaki
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Abstract

We report on the cosmic ray mass composition measured by the Telescope Array Low-energy Extension (TALE) hybrid detector. The TALE detector consists of a fluorescence detector (FD) station with 10 FD telescopes located at the Telescope Array (TA) Middle Drum FD Station (itself made up of 14 FD telescopes), and a surface detector (SD) array of scintillators. The array consists of 40 SDs with 400 m spacing and 40 SDs with 600 m spacing. In this paper, we present results on the measurement of the depth of shower maxima ($X_\mathrm{max}$) in the energy range from $10^{16.5}$ eV to $10^{18.5}$ eV collected over five years of the TALE hybrid detector. The $X_\mathrm{max}$ distributions were analyzed and compared with Monte Carlo simulations of proton, helium, nitrogen, and iron primaries, using the QGSJet II-04 hadronic interaction model. Our results indicate that the elongation rate of the mean $X_\mathrm{max}$, which is defined as the slope of $\langle X_\mathrm{max} \rangle$ versus cosmic ray energy, exhibits a break around $10^{17}$ eV. Up to this energy, the composition becomes increasingly heavy, characterized by a growing dominance of heavy nuclei and a steadily decreasing fraction of light primaries. Beyond this energy, the proton fraction increases significantly with energy. These findings suggest a transition from Galactic to extra-Galactic cosmic ray sources around the so-called second knee.

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Telescope Array Collaboration, R. U. Abbasi, T. Abu-Zayyad, M. Allen, J. W. Belz, D. R. Bergman, F. Bradfield, I. Buckland, W. Campbell, B. G. Cheon, K. Endo, A. Fedynitch, T. Fujii, K. Fujisue, K. Fujita, M. Fukushima, G. Furlich, A. Gálvez Ureña, Z. Gerber, N. Globus, T. Hanaoka, W. Hanlon, N. Hayashida, H. He, K. Hibino, R. Higuchi, D. Ikeda, D. Ivanov, S. Jeong, C. C. H. Jui, K. Kadota, F. Kakimoto, O. Kalashev, K. Kasahara, Y. Kawachi, K. Kawata, I. Kharuk, E. Kido, H. B. Kim, J. H. Kim, S. W. Kim, R. Kobo, I. Komae, K. Komatsu, K. Komori, A. Korochkin, C. Koyama, M. Kudenko, M. Kuroiwa, Y. Kusumori, M. Kuznetsov, Y. J. Kwon, K. H. Lee, M. J. Lee, B. Lubsandorzhiev, J. P. Lundquist, H. Matsushita, A. Matsuzawa, J. A. Matthews, J. N. Matthews, K. Mizuno, M. Mori, S. Nagataki, K. Nakagawa, M. Nakahara, H. Nakamura, T. Nakamura, T. Nakayama, Y. Nakayama, K. Nakazawa, T. Nonaka, S. Ogio, H. Ohoka, N. Okazaki, M. Onishi, A. Oshima, H. Oshima, S. Ozawa, I. H. Park, K. Y. Park, M. Potts, M. Przybylak, M. S. Pshirkov, J. Remington, C. Rott, G. I. Rubtsov, D. Ryu, H. Sagawa, N. Sakaki, R. Sakamoto, T. Sako, N. Sakurai, S. Sakurai, D. Sato, K. Sekino, T. Shibata, J. Shikita, H. Shimodaira, H. S. Shin, K. Shinozaki. 2026-03-16. Cosmic ray mass composition measurement in the energy range from $10^{16.5}$ eV to $10^{18.5}$ eV observed with the TALE hybrid detector. https://doi.org/10.1103/vrky-dxn7

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