ANALYSIS OF LARGE-SCALE ANISOTROPY OF ULTRA-HIGH ENERGY COSMIC RAYS IN HiRes DATA

Abstract

Stereo data collected by the HiRes experiment over a six year period are\nexamined for large-scale anisotropy related to the inhomogeneous distribution\nof matter in the nearby Universe. We consider the generic case of small\ncosmic-ray deflections and a large number of sources tracing the matter\ndistribution. In this matter tracer model the expected cosmic ray flux depends\nessentially on a single free parameter, the typical deflection angle theta. We\nfind that the HiRes data with threshold energies of 40 EeV and 57 EeV are\nincompatible with the matter tracer model at a 95% confidence level unless\ntheta is larger than 10 degrees and are compatible with an isotropic flux. The\ndata set above 10 EeV is compatible with both the matter tracer model and an\nisotropic flux.\n