Measurement of the Cosmic Ray Energy Spectrum and Composition from 1017 to 1018.3 eV Using a Hybrid Fluorescence 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. 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. van der Velde, L. R. Wiencke, C. R. Wilkinson, S. Yoshida, X. Z. Zhang
Abstract
We study the spectrum and average mass composition of cosmic rays with primary energies between 1017 eV and 1018 eV using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. 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 f rom 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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