Abstract
A new hybrid experiment (YAC-II+Tibet-III+MD) located at Yangbajing has started to improve the capability of explicit measurements of the cosmic-ray components (P, He, CNO, Fe, etc) at the knee energy region since 2014. Considering the different features of air shower development for different primary cosmic-ray nuclei, using a full Monte Carlo simulation, we modified the lateral distribution functions for proton-induced, helium-induced and iron-induced air showers, respectively. The results show that the air shower size of different nuclei obtained by the modified Nishimura-Kamata-Greisen function is consistent with the true shower size within 5% systematic errors. Furthermore, we studied the Extensive Air Shower age parameter determination from the lateral distribution functions of charged particles near the air shower core with the Tibet hybrid experiment. The derived age parameter can be well used to estimate the particle type of the incident primary cosmic rays.
Highlights
The spectra of cosmic rays (CR) can be well described by a power law dj/dE ∝ E−γ over a very broad energy range, separated with some "spectral features"
For an air shower event, Tibet-III provides the arrival direction (θ) and the air shower size (Ne f it) which are interrelated to primary energy, YAC-II is used to record high energy core events, both of the two arrays measure the electromagnetic components generated by air showers, while muon-detector array (MD) is used to measure the high-energy μ component
We studied the separation of the mass composition by the (YAC-II+Tibet-III) and (YAC-II+TibetIII+MD) arrays, respectively, by using a feed-forward artificial neural network (ANN) method, whose applicability to our experiment was well confirmed by the Monte Carlo (MC) simulation [9]
Summary
The spectra of cosmic rays (CR) can be well described by a power law dj/dE ∝ E−γ over a very broad energy range, separated with some "spectral features". The power index suddenly steepens from approximately -2.7 to -3.1 at around 4 PeV, resulting in a distinctive "knee" shape in the spectrum [1], and the corresponding energy range is the so called "knee region". There is still controversy to its origin For this explanation, many authors have proposed various models such as a change of acceleration mechanisms at the sources of cosmic rays (supernova remnants, pulsars, etc.), an assumption of nearby sources emitting high energy cosmic rays, a change of cosmic ray propagation in the Galaxy (diffusion, drift, escape from the Galactic disk), and some unknown new processes in the atmosphere during air-shower development [5,6,7,8]. In order to resolve the origin of the knee, it is critical to measure the primary chemical composition or mass group at energies of 50 TeV–1016 eV, especially, to measure the primary energy spectra of individual
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