IceCube: From Oscillations to PeV Neutrino Events

With IceCube and its low-energy extension DeepCore, an instrument with a combined energy range from tens of GeV to EeV has been commissioned. It measures the atmospheric neutrino spectrum from the lower energies where neutrinos oscillate to energies as large as 100 TeV with a statistic of more than 100,000 events per year. The initial results suggest that IceCube can measure the oscillation parameters in an energy range that exceeds existing observations by one order of magnitude, thus opening a new window on neutrino physics. We also discuss the observation of PeV-energy events that cannot be accommodated by the flux anticipated by extrapolation of present atmospheric neutrino measurements.