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Abstract
Results from the IceCube Neutrino Observatory have recently provided compelling evidence for the existence of high energy astrophysical neutrinos, but that result was of limited sensitivity to muon-flavored neutrinos from the Northern sky.
In the analysis presented here, a data sample of approximately 35,000 muon neutrinos from the Northern sky was extracted from data taken during 659.5 days of livetime recorded between May 2010 and May 2012. Although this sample is composed primarily of neutrinos produced by cosmic ray interactions in the Earth's atmosphere, the highest energy events are inconsistent with a hypothesis of solely terrestrial origin at 3.7 sigma significance.
These neutrinos can, however, be explained by an astrophysical flux per neutrino flavor at a level of Phi(E) = 9.9{+3.9}{-3.4} times 10
-19GeV
-1 cm
-2 sr
-1 s
-1 (E / 100 TeV)
-2, in an energy range from 500 TeV-1.2PeV, consistent with the Southern hemisphere dominated result. Additionally, a fit for an astrophysical flux with an arbitrary spectral index was performed, and found an index of 2.2{+0.2}{-0.2}, which is also in good agreement with the Southern hemisphere result.
