Energy-dependent anisotropy of cosmic-ray muons: A twelve-year study with IceCube Neutrino Observatory

TL;DR

This twelve-year study using IceCube data reveals energy-dependent cosmic-ray muon anisotropy, showing strong large-scale patterns at low energies and localized structures at high energies, supporting diffusion models.

Contribution

First comprehensive energy-resolved analysis of cosmic-ray muon anisotropy with 12 years of IceCube data, contrasting low- and high-energy features using multiple analytical methods.

Findings

Strong dipolar anisotropy at low energies

Weaker, localized anisotropy at high energies

Energy distributions well fit by Gaussian models

Abstract

We present a comprehensive, energy-resolved study of cosmic-ray muon anisotropy using 12 years (2011-2023) of data from the IceCube Neutrino Observatory, comprising 7.92 x 10^11 events in the 13 TeV to 5.3 PeV energy range. Dividing the spectrum at log-scale energy 5 GeV, we contrast low- and high-energy anisotropy features via sidereal modulation, angular profiles, Fourier analysis, and full-sky HEALPix mapping. Gaussian and power-law fits to energy distributions are evaluated using chi-squared, reduced chi-squared, and Bayesian Information Criterion. Results show strong dipolar and large-scale anisotropy at low energies, likely due to geomagnetic and atmospheric effects, while high-energy muons display weaker, more localized structures consistent with reduced scattering and source-related anisotropy. Energy distributions are well fit by Gaussians, especially in the 6.5 to 100 bin, validating IceCube's reconstruction at PeV scales. These findings confirm energy-dependent anisotropy and support cosmic-ray diffusion models.