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