HiRes and TA Composition measurements

Abstract

In order to clarify the origin of ultra high energy cosmic rays (UHECRs), it is very important to determine the mass composition. The most effective strategy to determine the mass composition is Xmax technique. Xmax is the atmospheric depth of air shower maximum measured by fluorescence detectors (FDs). HiRes has reported Xmax measurement by FDs which indicated proton dominated mass composition. Now, Telescope Array (TA) experiment has also measured UHECRs with FDs. In this presentation, the detail of mass composition analysis and result of TA experiment will be reported and compared with HiRes experiment.