Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with 12 yr of Data Collected by the IceCube Neutrino Observatory

We analyzed the 7.92 × 10$^{11}$ cosmic-ray-induced muon events collected by the IceCube Neutrino Observatory
from 2011 May 13, when the fully constructed experiment started to take data, to 2023 May 12. This data set
provides an up-to-date cosmic-ray arrival direction distribution in the Southern Hemisphere with unprecedented
statistical accuracy covering more than a full period length of a solar cycle. Improvements in Monte Carlo event
simulation and better handling of year-to-year differences in data processing significantly reduce systematic
uncertainties below the level of statistical fluctuations compared to the previously published results. We confirm
the observation of a change in the angular structure of the cosmic-ray anisotropy between 10 TeV and 1 PeV, more
specifically in the 100–300 TeV energy range. For the first time, we analyzed the angular power spectrum at
different energies. The observed variations of the power spectra with energy suggest relatively reduced large-scale
features at high energy compared to those of medium and small scales. The large volume of data enhances the
statistical significance at higher energies, up to the PeV scale, and smaller angular scales, down to approximately 6° compared to previous findings.