Abstract
Measuring the knees of the cosmic ray spectra for individual species is a very important approach to solve the problem of the origin of ultra high energy galactic cosmic rays. The knee of the iron spectrum is implied to be above 10 PeV from previous experiments, such as ARGO-YBJ and LHAASO-WFCTA. LHAASO is a suitable size for measurements with the required precision. The key is to separate iron nuclei from all cosmic ray samples. In this paper, we identify a couple of variables that are sensitive to the composition of showers recorded by the detector arrays in LHAASO. A multi variate analysis is proposed for the separation. The efficiency and purity of the selection for demanded species are optimized by well configuring the LHAASO array using the LHAASO simulation tools.
Highlights
The most significant feature of the power-law-like spectrum of Cosmic Rays (CR) with all mixed species is the “knee", i.e. a significant bending of the spectrum from the power-law index of approximately -2.7 to -3.1 around a few PeV
We describe the Large High Altitude Air Shower Observatory (LHAASO) detector arrays that are relevant to the measurement in the second section, identify the parameters measured by LHAASO that are sensitive to the composition, and the selection of iron samples out of all shower events in the third section and report the preliminary results on the expectation of the spectrum measurement using the LHAASO simulation kit in the summary section
The LHAASO experiment will enable an effective identification of CR primary species by measuring two independent key parameters of the induced air showers, muon content and shower maximum position in the energy range from 10 to 100 PeV
Summary
The most significant feature of the power-law-like spectrum of Cosmic Rays (CR) with all mixed species is the “knee", i.e. a significant bending of the spectrum from the power-law index of approximately -2.7 to -3.1 around a few PeV. Disclosing the mechanism of the knee would be a significant improvement in understanding the origin of the galactic cosmic rays. A precise measurement of the knee of the iron spectrum is obviously very important to understand the mechanism of the knee. The composition measurement in the energy range above 10 PeV is really difficult because a rather large detector array is required due to the very low flux. A multi-parameter measurement is required to maintain a high resolution in the shower composition by providing sufficient information about the showers in identifying their composition.
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