Kara Hoffman, University of Maryland
May 6, 2014

In the summer of 2012, the IceCube Neutrino Observatory announced the observation of two neutrino interactions deep in the south polar icecap, each with energies in excess of 10^15 eV, making them the highest energy neutrinos ever observed. Further analysis and additional data revealed that these events formed the tail of a spectrum that is inconsistent with the background from neutrinos produced by cosmic ray interactions with the atmosphere. While the measured rates are consistent with longstanding theoretical predictions of an astrophysical neutrino flux, many questions remain. Where did they come from? Does the spectrum abruptly cut off just above a PeV, or is it steeply falling? Where is the flux of ultra high energy neutrinos that should be produced in cosmic ray interactions with the cosmic microwave background? I will review this exciting discovery and describe ongoing and future efforts in this quickly evolving field, which may lead to some answers.

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