Search for Anisotropy in the Ultra High Energy Cosmic Ray Spectrum using the Telescope Array Surface Detector

Understand

The Telescope Array (TA) experiment is located in the western desert of Utah, USA, and observes ultra high energy cosmic rays (UHECRs) in the Northern hemisphere.

• At the highest energies, $E>10$~EeV, the shape of cosmic ray energy spectrum may carry an imprint of the source density distribution along the line of sight different in different directions of the sky.
• In this study, we search for such directional variations in the shape of the energy spectrum using events observed with the Telescope Array's surface detector.
• We divide the TA field of view into two nearly equal-exposure regions: the "on-source" region which we define as $\pm 30^\circ$ of the supergalactic plane containing mostly nearby structures, and the complementary "off-source" region where the sources are further away on average.