Hybrid Measurement of the Energy Spectrum and Composition of Ultra-High Energy Cosmic Rays by the Telescope Array

Abstract

The energy spectrum and mass composition of Ultra-High Energy Cosmic Rays (UHECRs) above 10$^{18.2}$ eV measured by Telescope Array (TA) are presented. TA is the largest UHECR observatory in the northern hemisphere, located in the west desert of Utah, USA. It consists of 507 Surface Detectors (SDs) and three fluorescence detectors (FDs) to observe UHECRs by those two types of detectors simultaneously, in so called hybrid observation. In hybrid analysis, a reconstruction of the longitudinal development of the air shower observed by FD with the information at the ground observed by SD, can measure the energy of the primary cosmic ray and the depth of the shower maximum precisely. The performance of the analysis, energy spectrum and mass composition of UHECR measurd by TA hybrid data is discussed.