MEASUREMENT OF THE ANISOTROPY OF COSMIC-RAY ARRIVAL DIRECTIONS WITH ICECUBE

Abstract

We report the first observation of an anisotropy in the arrival direction of\ncosmic rays with energies in the multi TeV region in the Southern sky using\ndata from the IceCube detector. Between June 2007 and March 2008, the\npartially-deployed IceCube detector was operated in a configuration with 1320\ndigital optical sensors distributed over 22 strings at depths between 1450 and\n2450 meters inside the Antarctic ice. IceCube is a neutrino detector, but the\ndata are dominated by a large background of cosmic ray muons. Therefore, the\nbackground data are suitable for high-statistics studies of cosmic rays in the\nSouthern sky. The data include 4.3 billion muons produced by downgoing cosmic\nray interactions in the atmosphere; these events were reconstructed with a\nmedian angular resolution of 3 degrees and a median energy of $\\sim20$ TeV.\nTheir arrival direction distribution exhibits an anisotropy in right ascension\nwith a first harmonic amplitude of $(6.4\\pm0.2 $stat$. \\pm 0.8\n$syst$.)\\times10^{-4}$.\n