Abstract
The results on ultra-high energy cosmic rays’ chemical composition based on the data from the Telescope Array surface detector are reported. The analysis is based the boosted decision tree (BDT) multivariate analysis built upon 14 observables related to both the properties of the shower front and the lateral distribution function. The multivariate classifier is trained with Monte-Carlo sets: proton-induced, which is considered as background events, and ironinduced, considered as signal events. The classifier results in a single variable ξ for data and Monte-Carlo sets, available for one-dimensional analysis. The data to Monte-Carlo comparison results in an average atomic mass of UHECR for energy range 1018:0 - 1020:0 eV. The average atomic mass of primary particles corresponds to 〈ln A〉 = 1:52± 0:08(stat.)± 0:1(syst.). The comparison with TA hybrid composition results and the other experiments is presented.
Highlights
Ultra-high-energy cosmic rays (UHECRs) are particles and nuclei of energies more than 1018 eV entering the Earth atmosphere
While UHECRs are registered for many years, their origin remains a puzzle for physicists
Knowledge of the UHECR mass composition is crucial for understanding the source mechanism and propagation of cosmic rays
Summary
Ultra-high-energy cosmic rays (UHECRs) are particles and nuclei of energies more than 1018 eV entering the Earth atmosphere. Two large-scale EAS facilities: Pierre Auger Observatory [1] at Southern hemisphere and Telescope Array [2] at Northern hemisphere operate in the hybrid mode, measuring both the particle flux on the ground with the surface detectors and the emitted fluorescence light with the fluorescence telescopes. The Telescope Array is an experiment designed for observation of extensive air showers from high energy cosmic rays, located in Utah, USA. A method of composition studies with the Telescope Array surface detector (SD) data is suggested. The main advantage of SD data usage is that surface detectors obtain much more data than fluorescense telescopes, which can operate only on clear moonless nights (10 % duty cycle).
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