A measurement of the cosmic-ray primary composition between 3 × 1013 and 3 × 1015 eV using underground muons

D. Cebula, University of Pennsylvania
S. C. Corbató, University of Pennsylvania
T. Daily, University of Pennsylvania
D. B. Kieda, University of Pennsylvania
K. Lande, University of Pennsylvania
C. K. Lee, University of Pennsylvania
M. L. Cherry, Louisiana State University


The multiplicities of high-energy muons (Eμ > 2.6 TeV) detected deep underground by the Homestake liquid scintillation hodoscope are examined for sensitivity to the cosmic-ray primary composition in the energy range from 3 × 1013 to 3 × 1015 eV. Using a two-component (proton and iron) energy-independent composition model, we find the best primary composition model contains 83% ± 13% protons and 17% iron. Using an energy-dependent five-component model, we find the multiple muon rates are in good agreement (67.4% χ2 probability) with a proton-dominated primary composition, as suggested by Fichtel and Linsley. An iron-enriched primary composition does not provide a good fit to the experimental data (0.38% χ2 probability).