Measurement of the cosmic-ray energy spectrum and composition from 1017 to 1018.3 eV using a hybrid technique

T. Abu-Zayyad, K. Belov, D. J. Bird, J. Boyer, Z. Cao, M. Catanese, G. F. Chen, R. W. Clay, C. E. Covault, H. Y. Dai, B. R. Dawson, J. W. Elbert, B. E. Fick, L. F. Fortson, J. W. Fowler, K. G. Gibbs, M. A.K. Glasmacher, K. D. Green, Y. Ho, A. HuangC. C. Jui, M. J. Kidd, D. B. Kieda, B. C. Knapp, S. Ko, C. G. Larsen, W. Lee, E. C. Loh, E. J. Mannel, J. Matthews, J. N. Matthews, B. J. Newport, D. F. Nitz, R. A. Ong, K. M. Simpson, J. D. Smith, D. Sinclair, P. Sokolsky, P. Sommers, C. Song, J. K.K. Tang, S. B. Thomas, J. C. Van Der Velde, L. R. Wiencke, C. R. Wilkinson, S. Yoshida, X. Z. Zhang

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189 Scopus citations


We study the spectrum and average mass composition of cosmic rays with primary energies between 1017 and 1018 eV using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the Michigan Muon Array (MIA). Measurements have been made of the change in the depth of shower maximum as a function of energy. A complete Monte Carlo simulation of the detector response and comparisons with shower simulations leads to the conclusion that the cosmic-ray intensity is changing from a heavier to a lighter composition in this energy range. The spectrum is consistent with earlier Fly's Eye measurements and supports the previously found steepening near 4 × 1017 eV.

Original languageEnglish (US)
Pages (from-to)686-699
Number of pages14
JournalAstrophysical Journal
Issue number2 PART 1
StatePublished - Aug 20 2001


  • Cosmic rays
  • ISM: abundances

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