Sensitivity of the Tibet hybrid experiment (Tibet-III plus MD) for primary proton spectrum between 30 TeV and a few hundreds of TeV's

In the Tibet AS gamma experiment, continuous observation of cosmic rays and cosmic gamma rays from TeV to tens of PeV has been carried out using a hybrid detector that combines the air shower detector array (Tibet-III) and the water Cherenkov muon detector array (MD). To measure the proton spectrum from 30 TeV to 400 TeV, we developed a proton-shower selection method using the difference of the number of muons in the air shower depending on the primary nuclide. In the Monte Carlo simulations to evaluate the performance of this method, we used a Heavy-dominant model in which the proportion of heavy nuclei in the "knee" region gradually increases and a Helium-rich model in which the proportion of Helium gradually increases as the primary cosmic ray chemical composition model, and the QGSJET-II-04 and the SIBYLL 2.3c were used as the shower interaction models. This method made it possible to select protons with a purity of 90%, and the detection efficiency of protons was approximately 17.8% at 30 TeV and 8.6% at 400 TeV respectively. The energy resolution of the selected protons was approximately 53% at 30 TeV and 27% at 400 TeV respectively. The total systematic error of the proton flux depending on these models was found to be approximately +/- 36%. These results indicate that the new hybrid measurement method is powerful enough to study the proton spectrum in the knee region.