Icy window on the physics of cosmic neutrinos

High-energy astrophysical neutrinos can thus be observed by instruments that detect Cherenkov radiation in such a medium. Because the expected fluxes in the number of astrophysical neutrinos at the energy levels of interest are low, and these fluxes are thought to decrease rapidly as the energy of neutrinos increases2, large volumes of the transparent medium are needed. Roughly 5% of the neutrino energy in these events is expected to be taken up by secondary particles that are neutral or don't have enough energy to produce Cherenkov radiation5, limiting the amount of energy that can be observed to about 6.0 PeV. [...]low-energy muons are expected to be produced in the cascade, and to outrun the wavefront of the Cherenkov radiation at a high enough rate to trigger early pulses of light that would be detected by the DOMs. On the basis of the characteristics of the detected event, the authors classified it as having been caused by an astrophysical neutrino - the confidence of this classification was at the 5o level, which means that there is only about one chance in three million that it is wrong. [...]early light pulses were detected by the DOMs, consistent with the production of low-energy secondary muons from the decay of a W~ boson into hadrons.