Observation of anisotropy in the arrival direction distribution of cosmic rays above TeV energies with IceCube

The IceCube neutrino telescope, completed in December 2010, is a cubic-kilometer scale detector buried under the South Pole ice. Between May 2009 and May 2010, IceCube recorded 32 billion of atmospheric muons generated in air showers produced by cosmic rays in the TeV energy range. This high statistics data sample can be used to look for anisotropy in the arrival directions of the cosmic ray particles at the per-mille level. IceCube observes, for the first time in the southern hemisphere, an energy dependence in the Galactic cosmic ray anisotropy up to a few hundred TeV. This study shows that the same large-scale anisotropy observed at median energies around 20 TeV is not present at 400 TeV; the anisotropy observed at 400 TeV shows substantial differences with respect to that at lower energy. In addition to the large-scale features observed at 20 TeV in the form of strong dipole and quadrupole moments, the data include several localized regions of excess and deficit on scales between 10 degrees and 30 degrees. The features observed at both large and small scales are statistically significant, but their origin is currently unknown. Published by Elsevier B.V.