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First observation of PeV-energy neutrinos with IceCube

Abstract:

We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of 1.04±0.16 and 1.14±0.17 PeV, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current ν e, μ, τ (ν e, μ, τ) or charged-current ν e (ν 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±0.004 (stat)− 0.057+ 0.041 (syst). The probability of observing two or more candidate events under the atmospheric background-only hypothesis is 2.9× 10− 3 (2.8 σ) 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 …