We have been observing extensive air showers using the Tibet-III air shower array and the underground
water-Cherenkov muon detector array (MD) to determine the chemical composition of
cosmic rays with energies corresponding to the knee energy region. In previous studies, we developed
a method to acquire the proton spectrum in the energy range from 40 to 630 TeV via a hybrid
experiment using the Tibet-III and MD and investigated its performance. We conducted Monte
Carlo simulations showing that this method can separate protons with a purity of 90% and that the
maximum total systematic error of the proton flux depending on interaction models in air-shower
development is ±37%. In the present study, analysis results for data acquired over a period of 12
days in 2014 are presented. The abundances of proton-like showers to whole well-reconstructed
showers, including model dependence, are 9.1%–14.5% at ∼35 TeV and 1.8%–3.1% at ∼450 TeV.