Measurement of the Cosmic-Ray Energy Spectrum and Compositionfrom 1017 to 1018.3 eV Using a HybridTechnique

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. Huang; C. 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

doi:10.1086/322240

Measurement of the Cosmic-Ray Energy Spectrum and Composition from 10¹⁷ to 10^18.3 eV Using a Hybrid Technique

T. Abu-Zayyad¹, K. Belov¹, D. J. Bird², J. Boyer³, Z. Cao¹, M. Catanese⁴, G. F. Chen¹, R. W. Clay², C. E. Covault⁵, H. Y. Dai¹, B. R. Dawson², J. W. Elbert¹, B. E. Fick⁵, L. F. Fortson^5,6, J. W. Fowler⁵, K. G. Gibbs⁵, M. A. K. Glasmacher⁷, K. D. Green⁵, Y. Ho⁸, A. Huang¹, C. C. Jui¹, M. J. Kidd⁹, D. B. Kieda¹, B. C. Knapp³, S. Ko¹, C. G. Larsen¹, W. Lee⁸, E. C. Loh¹, E. J. Mannel³, J. Matthews^10,11, J. N. Matthews¹, B. J. Newport⁵, D. F. Nitz¹², R. A. Ong⁵, K. M. Simpson², J. D. Smith¹, D. Sinclair⁹, P. Sokolsky¹, P. Sommers¹, C. Song⁸, J. K. K. Tang¹, S. B. Thomas¹, J. C. van der Velde⁷, L. R. Wiencke¹, C. R. Wilkinson², S. Yoshida¹, and X. Z. Zhang⁸

© 2001. The American Astronomical Society. All rights reserved. Printed in U.S.A.
The Astrophysical Journal, Volume 557, Number 2 Citation T. Abu-Zayyad et al 2001 ApJ 557 686 DOI 10.1086/322240

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Author affiliations

¹ High Energy Astrophysics Institute, University of Utah, Salt Lake City, UT 84112

² University of Adelaide, Adelaide, S.A. 5005, Australia

³ Nevis Laboratory, Columbia University, Irvington, NY 10533

⁴ Smithsonian Astrophysics Observatory, Cambridge, MA 02138

⁵ Enrico Fermi Institute, University of Chicago, Chicago, IL 60637

⁶ Joint appointment with the Adler Planetarium and Astronomy Museum, Astronomy Department, 1300 South Lake Shore Drive, Chicago, IL 60605

⁷ University of Michigan, Ann Arbor, MI 48109

⁸ Department of Physics, Columbia University, New York, NY 10027

⁹ University of Illinois at Champaign-Urbana, Urbana, IL 61801

¹⁰ Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803

¹¹ Department of Physics, Southern University, Baton Rouge, LA 70801

¹² Department of Physics, Michigan Technological University, Houghton, MI 49931

Dates

Received 2000 October 18
Accepted 2001 April 17

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Abstract

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.

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