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The Cosmic-Ray Composition between 2 PeV and 2 EeV Observed with the TALE Detector in Monocular Mode

2021; IOP Publishing; Volume: 909; Issue: 2 Linguagem: Inglês

10.3847/1538-4357/abdd30

1538-4357

Rasha Abbasi, Mitsuru Abe, T. Abu‐Zayyad, M. Allen, Yuto Arai, E. Barcikowski, John Belz, D. R. Bergman, S. A. Blake, R. Cady, B. G. Cheon, J. Chiba, M. Chikawa, Toshihiro Fujii, Kozo Fujisue, K. Fujita, Ryota Fujiwara, M. Fukushima, Ryota Fukushima, G. Furlich, W. Hanlon, Motoki Hayashi, N. Hayashida, K. Hibino, R. Higuchi, K. Honda, D. Ikeda, Taichi Inadomi, Naoko Inoue, Takaaki Ishii, Hirotaka Ito, D. Ivanov, Hirokazu Iwakura, Hyeonju Jeong, S. Jeong, C. C. H. Jui, K. Kadota, F. Kakimoto, O. Kalashev, K. Kasahara, Saori Kasami, H. Kawai, S. Kawakami, S. Kawana, K. Kawata, E. Kido, Jihyun Kim, Jihyun Kim, Jihyun Kim, M. H. Kim, S. W. Kim, Yusuke Kimura, S. Kishigami, V. Kuzmin, M. Kuznetsov, Y.-J. Kwon, K. H. Lee, Б. Лубсандоржиев, Jon Paul Lundquist, K. Machida, Hiroyuki Matsumiya, T. Matsuyama, J. N. Matthews, R. Mayta, M. Minamino, K. Mukai, I. Myers, Shigehiro Nagataki, Kei Nakai, R. Nakamura, T. Nakamura, Yuya Nakamura, T. Nonaka, Hiroyuki Oda, S. Ogio, M. Ohnishi, H. Ohoka, Yuya Oku, T. Okuda, Y. Omura, M. Ono, R. Onogi, A. Oshima, S. Ozawa, Il Han Park, М. С. Пширков, Jackson Remington, D. Rodriguez, Г. Рубцов, Dongsu Ryu, H. Sagawa, Ryosuke Sahara, Yasunori Saito, Н. Сакаки, T. Sako, N. Sakurai, Kei Sano, K. Satô, T. Seki, K. Sekino, P. D. Shah, F. Shibata, Norimichi Shibata, T. Shibata, Hidetoshi Shimodaira, B. K. Shin, H. S. Shin, Daiki Shinto, J. D. Smith, P. Sokolsky, Naohiro Sone, B. T. Stokes, T. A. Stroman, T. Suzawa, Y. Takagi, Yoshiyuki Takahashi, M. Takamura, M. Takeda, Ryuji Takeishi, A. Taketa, M. Takita, Y. Tameda, H. Tanaka, K. Tanaka, M. Tanaka, Yuta Tanoue, S. B. Thomas, G. B. Thomson, P. Tinyakov, I. Tkachev, H. Tokuno, T. Tomida, S. Troitsky, Ryosuke Tsuda, Y. Tsunesada, Y. Uchihori, S. Udo, Takafumi Uehama, F. Urban, Tony Wong, Kohei Yada, M. Yamamoto, K. Yamazaki, J. Yang, K. Yashiro, Fugo Yoshida, Y. Zhezher, Z. Zundel,

Particle physics theoretical and experimental studies

We report on a measurement of the cosmic ray composition by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). By making use of the Cherenkov light signal in addition to air fluorescence light from cosmic ray (CR) induced extensive air showers, the TALE FD can measure the properties of the cosmic rays with energies as low as $\sim 2$ PeV and exceeding 1 EeV. In this paper, we present results on the measurement of $X_{\rm max}$ distributions of showers observed over this energy range. Data collected over a period of $\sim 4$ years was analyzed for this study. The resulting $X_{\rm max}$ distributions are compared to the Monte Carlo (MC) simulated data distributions for primary cosmic rays with varying composition and a 4-component fit is performed. The comparison and fit are performed for energy bins, of width 0.1 or 0.2 in $\log_{10} (E/{\rm eV})$, spanning the full range of the measured energies. We also examine the mean $X_{\rm max}$ value as a function of energy for cosmic rays with energies greater than $10^{15.8}$ eV. Below $10^{17.3}$ eV, the slope of the mean $X_{\rm max}$ as a function of energy (the elongation rate) for the data is significantly smaller than that of all elements in the models, indicating that the composition is becoming heavier with energy in this energy range. This is consistent with a rigidity-dependent cutoff of events from galactic sources. Finally, an increase in the $X_{\rm max}$ elongation rate is observed at energies just above $10^{17}$ eV indicating another change in the cosmic rays composition.