A search for high-energy neutrinos was performed using data collected by the IceCube Neutrino Observatory from May 2009 to May 2010 , when the array was running in its 59-string configuration .
The data sample was optimized to contain muon neutrino induced events with a background contamination of atmospheric muons of less than 1 % .
These data , which are dominated by atmospheric neutrinos , are analyzed with a global likelihood fit to search for possible contributions of prompt atmospheric and astrophysical neutrinos , neither of which have yet been identified .
Such signals are expected to follow a harder energy spectrum than conventional atmospheric neutrinos .
In addition , the zenith angle distribution differs for astrophysical and atmospheric signals .
A global fit of the reconstructed energies and directions of observed events is performed , including possible neutrino flux contributions for an astrophysical signal and atmospheric backgrounds as well as systematic uncertainties of the experiment and theoretical predictions .
The best fit yields an astrophysical signal flux for \nu _ { \mu } + \bar { \nu } _ { \mu } of E ^ { 2 } \cdot \Phi ( E ) = 0.25 \cdot 10 ^ { -8 } \textrm { GeV } \textrm { cm } ^ { -2 } \textrm { s% } ^ { -1 } \textrm { sr } ^ { -1 } , and a zero prompt component .
Although the sensitivity of this analysis for astrophysical neutrinos surpasses the Waxman and Bahcall upper bound , the experimental limit at 90 % confidence level is a factor of 1.5 above at a flux of E ^ { 2 } \cdot \Phi ( E ) = 1.44 \cdot 10 ^ { -8 } \textrm { GeV } \textrm { cm } ^ { -2 } \textrm { s% } ^ { -1 } \textrm { sr } ^ { -1 } .