High energy neutrinos undetected in IceCube

High energy neutrinos are expected to come out of gamma ray bursts. On earth there is a IceCube, which is designed to catch these neutrinos. However, after 13 months of run, they find null results. [http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.141101]

GRBs result from a giant star explosion or the collision of star remnants. These cosmic cataclysms produce—in addition to gamma rays—high-speed protons that are thought to account for the highest energy cosmic rays observed on Earth. Near the source, these protons may run into photons and end up generating neutrinos with energies far above 1 TeV. In the past, neutrino detectors on Earth have not been large enough to capture one of these high-energy neutrinos with any likelihood.

IceCube, which was completed in December 2010, is a kilometer-cubed array of photodetectors that have been drilled down into the Antarctic ice cap. Neutrinos typically fly through the array without leaving a trace, but occasionally one will collide with a nucleus and create a charged particle that emits light as it moves through the ice. The IceCube team compared 13 months of their data (collected when the array was half finished) to observations of 117 GRBs measured independently over the same time period. Contrary to expectations, no high-energy neutrinos were detected within a half-hour of each GRB. Theorists may need to rethink their models of GRBs, as well as look for other possible sources for the highest energy cosmic rays. – Michael Schirber