Evidence for Changing of Cosmic Ray Composition between1017and1018eV from Multicomponent Measurements

T. Abu-Zayyad, K. Belov, D. J. Bird, J. Boyer, Z. Cao, M. Catanese, G. F. Chen, R. W. Clay, C. E. Covault, J. W. Cronin, H. Y. Dai, B. R. Dawson (+36 others)
2000 Physical Review Letters  
The average mass composition of cosmic rays with primary energies between 10^17eV and 10^18eV has been studied 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, X_max, and in the change in the muon density at a fixed core location, ρ_μ(600m), as a function of energy. The composition has also been evaluated in terms of the combination of X_max and ρ_μ(600m). The
more » ... nd ρ_μ(600m). The results show that the composition is changing from a heavy to lighter mix as the energy increases.
doi:10.1103/physrevlett.84.4276 pmid:10990665 fatcat:z6zl7z43kbgvpi6uacw6kr3ism