| Abstract: | The IceCube Neutrino Observatory has accumulated a total of 318 billion
cosmic-ray induced muon events between May 2009 and May 2015. This data set was
used for a detailed analysis of the cosmic-ray arrival direction anisotropy in
the TeV to PeV energy range. The observed global anisotropy features large
regions of relative excess and deficit, with amplitudes on the order of
$10^{-3}$ up to about 100 TeV. A decomposition of the arrival direction
distribution into spherical harmonics shows that most of the power is contained
in the low-multipole ($ellleq 4$) moments. However, higher multipole
components are found to be statistically significant down to an angular scale
of less than $10^{circ}$, approaching the angular resolution of the detector.
Above 100 TeV, a change in the morphology of the arrival direction distribution
is observed, and the anisotropy is characterized by a wide relative deficit
whose amplitude increases with primary energy up to at least 5,PeV, the
highest energies currently accessible to IceCube. No time dependence of the
large- and small-scale structures is observed in the six-year period covered by
this analysis. The high-statistics data set reveals more details on the
properties of the anisotropy and is potentially able to shed light on the
various physical processes that are responsible for the complex angular
structure and energy evolution. |
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