Analysis of large-scale anisotropy of ultra-high energy cosmic rays in HiRes data

Understand

Stereo data collected by the HiRes experiment over a six year period are examined for large-scale anisotropy related to the inhomogeneous distribution of matter in the nearby Universe.

• We consider the generic case of small cosmic-ray deflections and a large number of sources tracing the matter distribution.
• In this matter tracer model the expected cosmic ray flux depends essentially on a single free parameter, the typical deflection angle theta.
• We find that the HiRes data with threshold energies of 40 EeV and 57 EeV are incompatible with the matter tracer model at a 95% confidence level unless theta is larger than 10 degrees and are compatible with an isotropic flux.