Anisotropy in Cosmic-Ray Arrival Directions Using IceCube and IceTop

The IceCube Neutrino Observatory recorded more than 250 billion cosmic-ray induced muon events between May 2009 and May 2014. We use this data set to study the anisotropy in the arrival direction distribution of cosmic rays in the TeV to PeV energy range. The anisotropy features large regions of relative excess and deficit with amplitude on the order of 10−3. A decomposition of the arrival direction distribution into spherical harmonics shows that most of the power is contained in the low-multipole (`≤ 4) moments. However, higher multipole components are also statistically significant down to an angular scale of less than 10◦. The data set also allows for a detailed study of the anisotropy for various cosmic-ray median energies. The large-scale structure observed at energies near 20 TeV reaches a minimum amplitude, accompanied by a change in phase, around 150 TeV. At higher energies, we observe a strong deficit with an amplitude increasing with energy up to 5 PeV, the highest energies currently accessible to IceCube. The deficit is also present in IceTop maps of similar energies. No time-dependence of the large-scale structure was observed in the five-year period covered by this analysis.