A search for high-energy neutrinos interacting within the IceCube detector between 2010 and 2012 provided the first evidence for a high-energy neutrino flux of extraterrestrial origin. Results from an analysis using the same methods with a third year (2012–2013) of data from the complete IceCube detector are consistent with the previously reported astrophysical flux in the 100 TeV–PeV range at the level of ${10}^{-8}\mathrm{GeV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$ per flavor and reject a purely atmospheric explanation for the combined three-year data at $5.7\sigma$. The data are consistent with expectations for equal fluxes of all three neutrino flavors and with isotropic arrival directions, suggesting either numerous or spatially extended sources. The three-year data set, with a live time of 988 days, contains a total of 37 neutrino candidate events with deposited energies ranging from 30 to 2000 TeV. The 2000-TeV event is the highest-energy neutrino interaction ever observed.

We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of $1.04\pm 0.16$ and $1.14\pm 0.17\mathrm{PeV}$, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current ${\nu }_{e,\mu ,\tau }$ (${\overline{\nu }}_{e,\mu ,\tau }$) or charged-current ${\nu }_e$ (${\overline{\nu }}_e$) interactions within the IceCube detector. The events were discovered in a search for ultrahigh energy neutrinos using data corresponding to 615.9 days effective live time. The expected number of atmospheric background is $0.082\pm 0.004(\mathrm{stat}{)}_{-0.057}^{+0.041}(\mathrm{syst})$. The probability of observing two or more candidate events under the atmospheric background-only hypothesis is $2.9\times {10}^{-3}$ ($2.8\sigma$) taking into account the uncertainty on the expected number of background events. These two events could be a first indication of an astrophysical neutrino flux; the moderate significance, however, does not permit a definitive conclusion at this time.

The IceCube Collaboration has previously discovered a high-energy astrophysical neutrino flux using neutrino events with interaction vertices contained within the instrumented volume of the IceCube detector. We present a complementary measurement using charged current muon neutrino events where the interaction vertex can be outside this volume. As a consequence of the large muon range the effective area is significantly larger but the field of view is restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have been analyzed using a likelihood approach based on the reconstructed muon energy and zenith angle. At the highest neutrino energies between and a significant astrophysical contribution is observed, excluding a purely atmospheric origin of these events at significance. The data are well described by an isotropic, unbroken power-law flux with a normalization at neutrino energy of and a hard spectral index of . The observed spectrum is harder in comparison to previous IceCube analyses with lower energy thresholds which may indicate a break in the astrophysical neutrino spectrum of unknown origin. The highest-energy event observed has a reconstructed muon energy of which implies a probability of less than for this event to be of atmospheric origin. Analyzing the arrival directions of all events with reconstructed muon energies above no correlation with known γ-ray sources was found. Using the high statistics of atmospheric neutrinos we report the current best constraints on a prompt atmospheric muon neutrino flux originating from charmed meson decays which is below 1.06 in units of the flux normalization of the model in Enberg et al.

This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current ${\nu }_{\mu }$ interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With $1.27\times {10}^{20}$ 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of $336\pm 14$ events. The data are consistent with ${\nu }_{\mu }$ disappearance via oscillations with $|\Delta m_{32}^2|={2.74}_{-0.26}^{+0.44}\times {10}^{-3}{\mathrm{eV}}^2$ and ${sin}^2(2{\theta }_{23})>0.87$ (68% C.L.).