Search for Large-scale Anisotropy on Arrival Directions of Ultra-high-energy Cosmic Rays Observed with the Telescope Array Experiment

TL;DR

This study searches for large-scale anisotropy in ultra-high-energy cosmic rays using 11 years of Telescope Array data, finding results compatible with isotropy and previous dipole reports, but no definitive anisotropy detected.

Contribution

It provides the first large-scale anisotropy search with the Telescope Array data, setting upper limits and comparing results with the Pierre Auger Observatory.

Findings

Dipole amplitude of 3.3% with large uncertainty

Upper limit on dipole amplitude is 7.3% at 99% confidence

Results are consistent with isotropy and Auger findings

Abstract

Motivated by the detection of a significant dipole structure in the arrival directions of ultrahigh-energy cosmic rays above 8 EeV reported by the Pierre Auger Observatory (Auger), we search for a large-scale anisotropy using data collected with the surface detector array of the Telescope Array Experiment (TA). With 11 years of TA data, a dipole structure in a projection of the right ascension is fitted with an amplitude of 3.3+- 1.9% and a phase of 131 +- 33 degrees. The corresponding 99% confidence-level upper limit on the amplitude is 7.3%. At the current level of statistics, the fitted result is compatible with both an isotropic distribution and the dipole structure reported by Auger.