| Abstract: | We report on the observation of anisotropy in the arrival direction
distribution of cosmic rays at PeV energies. The analysis is based on data
taken between 2009 and 2012 with the IceTop air shower array at the South Pole.
IceTop, an integral part of the IceCube detector, is sensitive to cosmic rays
between 100 TeV and 1 EeV. With the current size of the IceTop data set,
searches for anisotropy at the 10^-3 level can, for the first time, be extended
to PeV energies. We divide the data set into two parts with median energies of
400 TeV and 2 PeV, respectively. In the low energy band, we observe a strong
deficit with an angular size of about 30 degrees and an amplitude of (-1.58 +/-
0.46 (stat) +/- 0.52 (sys)) x 10^(-3) at a location consistent with previous
observations of cosmic rays with the IceCube neutrino detector. The study of
the high energy band shows that the anisotropy persists to PeV energies and
increases in amplitude to (-3.11 +/- 0.38 (stat) +/- 0.96 (sys)) x 10^(-3). |
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