Probing the origin of cosmic-rays with extremely high energy neutrinos
  using the IceCube Observatory
  We have searched for extremely high energy neutrinos using data taken with
the IceCube detector between May 2010 and May 2012. Two neutrino induced
particle shower events with energies around 1 PeV were observed, as reported
previously. In this work, we investigate whether these events could originate
from cosmogenic neutrinos produced in the interactions of ultra-high energy
cosmic-rays with ambient photons while propagating through intergalactic space.
Exploiting IceCube's large exposure for extremely high energy neutrinos and the
lack of observed events above 100 PeV, we can rule out the corresponding models
at more than 90% confidence level. The model independent quasi-differential 90%
CL upper limit, which amounts to $E^2 \phi_{\nu_e + \nu_\mu + \nu_\tau} = 1.2
\times 10^{-7}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ at 1 EeV, provides the most
stringent constraint in the energy range from 10 PeV to 10 EeV. Our observation
disfavors strong cosmological evolution of the highest energy cosmic ray
sources such as the Fanaroff-Riley type II class of radio galaxies.
