IceCube Search for Anisotropy in Neutrino Data

Also out this week is a paper by IceCube in which they search for an anisotropy in the spatial distribution of very high energy cosmic ray neutrinos. This is basically just a search for point sources of these neutrinos on top of a more or less uniform background. Point sources would be very exciting because then we might be able to figure out what kinds of objects create these neutrinos.

IceCube is an enormous detector located at the South Pole. It consists of photodetectors dropped into holes bored in the Antarctic ice and looks for Cherenkov radiation from high energy particles created in neutrino interactions in the ice. The whole detector has a volume of around a cubic kilometer: far larger than any detector we could feasibly construct instead of using a natural target like ice in Antarctica.

In this search, IceCube searches for an anisotropy in two ways: a multipole expansion (decomposition of the spatial distribution to spherical harmonics) and an autocorrelation-based statistical test. In both methods they find results consistent with and actually slightly smoother than expected backgrounds.