Abstract
We have upgraded the new Tibet ASgamma experiment in China since 2014 to measure the chemical composition of cosmic rays around the knee. This hybrid experiment consist of an air-shower-core detector array (YAC-II) to detect high energy electromagnetic component, the Tibet air-shower array (Tibet-III) and a large underground water-Cherenkov muon-detector array (MD). We have carried out a detailed air-shower Monte Carlo (MC) simulation to study the performance of the hybrid detectors by using CORSIKA (version 7.5000), which includes EPOS-LHC, QGSJETII-04, SIBYLL2.1 and SIBYLL2.3 hadronic interaction models. The preliminary results of the interaction model checking above 50 TeV energy region are reported in this paper, and the primary proton and helium spectra in the energy range 50 TeV to 1015 eV was derived from YAC-I data and is smoothly connected with direct observation data at lower energies and also with our previously reported works at higher energies within statistical errors. The knee of the (P+He) spectra is located around 400 TeV. The interaction model dependence in deriving the primary (P+He) spectra is found to be small (less than 25% in absolute intensity, 10% in position of the knee), and the composition model dependence is less than 10% in absolute intensity.
Highlights
The all-particle energy spectrum of primary cosmic rays can be well described by a power law dj/dE ∝ E−γ over many orders of magnitude, with the power index γ changing sharply from 2.7 to 3.1 at about 4 PeV [1, 2]
We will report the primary proton and helium spectra in the energy range from 50 TeV to 1015 eV derived from Yangbajing air-shower Core detector array (YAC)-I data based on the newest interaction models (EPOS-LHC, QGSJETII-04, SIBYLL2.1 and SIBYLL2.3)
We examine four cases, (EPOS-LHC + He-poor), (QGSJETII-04 + He-poor), (SIBYLL2.1+He-poor) and (SIBYLL2.3+Hepoor) models
Summary
The all-particle energy spectrum of primary cosmic rays can be well described by a power law dj/dE ∝ E−γ over many orders of magnitude, with the power index γ changing sharply from 2.7 to 3.1 at about 4 PeV [1, 2]. In order to explicitly observe the break point of the spectral index for individual chemical component, we have recently upgraded the Tibet-EC experiment and started a new Tibet-YAC experiment, for reasons as follow: The Tibet-EC experiment was carried out to measure the Proton and Helium spectrum around the knee by detecting high energy electromagnetic particles at the air-shower core with a detection threshold of the core energy 20 TeV (the corresponding primary energy is several times 100 TeV) Such high-energy shower cores can be mostly generated by light primary nuclei penetrating deep in the atmosphere. We will report the primary proton and helium spectra in the energy range from 50 TeV to 1015 eV derived from YAC-I data based on the newest interaction models (EPOS-LHC, QGSJETII-04, SIBYLL2.1 and SIBYLL2.3)
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