Results from the IceCube Neutrino Observatory have recently provided compelling evidence for the existence of a high energy astrophysical neutrino flux utilizing a dominantly Southern Hemisphere dataset consisting primarily of \nu _ { e } and \nu _ { \tau } charged current and neutral current ( cascade ) neutrino interactions .
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 .
While 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 _ { \nu } ) = 9.9 ^ { +3.9 } _ { -3.4 } \times 10 ^ { -19 } \mathrm { GeV } ^ { -1 } \mathrm { cm } % ^ { -2 } \mathrm { sr } ^ { -1 } \mathrm { s } ^ { -1 } \left ( { E _ { \nu } \over 100 \mathrm { TeV } } % \right ) ^ { -2 } , consistent with IceCube ’ s Southern Hemisphere dominated result .
Additionally , a fit for an astrophysical flux with an arbitrary spectral index was performed .
We find a spectral index of 2.2 ^ { +0.2 } _ { -0.2 } , which is also in good agreement with the Southern Hemisphere result .