Abstract
The origin of ultra-high energy cosmic rays (UHECRs) has been a longstanding mystery. The Telescope Array (TA) is the largest experiment in the northern hemisphere observing UHECR in Utah, USA. It aims to reveal the origin of UHECR by studying the energy spectrum, mass composition and anisotropy of cosmic rays. TA is a hybrid detector comprised of three air fluorescence stations which measure the fluorescence light induced from cosmic ray extensive air showers, and 507 surface scintillator counters which sample charged particles from air showers on the ground. We present the cosmic ray spectrum observed with the TA experiment. We also discuss our results from measurement of the mass composition. In addition, we present the results from the analysis of anisotropy, including the excess of observed events in a region of the northern sky at the highest energy. Finally, we introduce the TAx4 experiment which quadruples TA, and the TA low energy extension (TALE) experiment.
Highlights
Ultra-high energy cosmic rays (UHECRs) are cosmic rays with energies larger than about 1018 eV
One of the methods to observe air showers is to use a surface detector (SD) array, which samples charged particles on the ground. Another method is performed by a fluorescence detector (FD), which measures fluorescence light generated by air shower development in the sky
The air shower longitudinal development can be measured by the FD, so the Telescope Array (TA) FD data are used for the composition analysis
Summary
Ultra-high energy cosmic rays (UHECRs) are cosmic rays with energies larger than about 1018 eV. UHECRs are observed by using cascade reactions of primary cosmic rays with atmospheric particles, which are called air showers. Using air shower particle information observed on the ground and an air shower Monte-Carlo (MC) simulation, the energy and arrival direction of primary cosmic rays are reconstructed. One of the methods to observe air showers is to use a surface detector (SD) array, which samples charged particles on the ground. Another study from the Auger experiment describes the discrepancy between observed hadronic signals and simulated [3] They suggest present hadronic models used in air shower MCs do not fully reproduce UHE air showers. The Telescope Array (TA) is the largest cosmic ray observatory in the Northern hemisphere [1]. In this paper we will present the results based on the analysis of the 9 years of TA data
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