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【摘要】

In this seminar, I will present two topics related to cosmic ray research. The first part will focus on the observation of ultra-high-energy cosmic rays with the TAx4 Surface Detector (SD) array, an extension of the SD array of the Telescope Array (TA) experiment, expressly designed to study cosmic rays with energies greater than 50 EeV to elucidate the origin of the ultra-high-energy cosmic rays. I will present the performance of the TAx4 SD array and its first observational result: the ultra-high-energy cosmic ray energy specturm. The second part is the Global Spline Fit (GSF), a data-driven model for cosmic-ray flux and mass composition. The GSF combines direct and indirect measurements of cosmic-ray flux of individual elements from 1 GeV to 100 EeV, considering their uncertainties. Since the original work of the GSF was presented in 2017, many new measurements have been published by both direct and indirect cosmic-ray experiments. I will show an updated GSF, incoporating datasets from the past seven years, and discuss the impact of the newly added data on the cosmic-ray flux and mass composition.