Anisotropy search in Energy distribution in Northern hemisphere using Telescope Array Surface Detector data

Abstract

The Telescope Array (TA) experiment is located in the western desert of Utah, USA, and observes ultra-high energy cosmic rays in the northern hemisphere. In the region of highest energies, the shape of cosmic ray energy spectrum may contain information on the source density distribution and chemical composition. In this study, using events observed with Telescope Array surface detector, we search for directional differences in the shape of energy spectrum. Observed cosmic ray energy spectra are compared between sky areas that have larger density of nearby objects, such as the super-galactic plane, and others that do not. If there were a direction that contains a nearby source or events of heavier composition at higher energies, there should be an enhancement of the probability to observe coincidences of arrival direction between high energy and low energy events. Based on this idea, we searched for such an enhancement. We report on results of those studies.