Large- and Medium-Scale Anisotropies in the Arrival Directions of Cosmic Rays observed with KASCADE-Grande

TL;DR

This study uses a novel analysis method on extensive cosmic ray data from KASCADE-Grande, finding no large-scale anisotropy but detecting a significant medium-scale anisotropic feature at around 33 PeV.

Contribution

The paper introduces a new maximum-likelihood method to analyze cosmic ray anisotropies, effectively reducing detector-induced biases and revealing medium-scale anisotropic features.

Findings

No large-scale dipole anisotropy detected.

A medium-scale anisotropic feature with 4σ significance identified.

Results suggest localized cosmic ray sources or structures.

Abstract

We search for anisotropies in the arrival directions of cosmic rays observed by the KASCADE-Grande air shower experiment. The analysis is based on public data of about 23.7 million events with reconstructed primary energies above 1 PeV. We apply a novel maximum-likelihood reconstruction method for the cosmic ray anisotropy, that compensates for spurious anisotropies induced by local detector effects. We find no evidence for a large-scale dipole anisotropy in the data, consistent with official results based on the conventional East-West derivative method. On the other hand, a subset of cosmic rays with median energy of 33 PeV shows strong evidence for a medium-scale feature with an angular diameter of 40 degrees. After accounting for the look-elsewhere effect, the post-trial significance of this medium-scale feature is at the level of 4$\sigma$.