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Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector

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      Abstract

      We report on results of an all-sky search for high-energy neutrino events interacting within the IceCube neutrino detector conducted between May 2010 and May 2012. The search follows up on the previous detection of two PeV neutrino events, with improved sensitivity and extended energy coverage down to approximately 30 TeV. Twenty-six additional events were observed, substantially more than expected from atmospheric backgrounds. Combined, both searches reject a purely atmospheric origin for the twenty-eight events at the \(4\sigma\) level. These twenty-eight events, which include the highest energy neutrinos ever observed, have flavors, directions, and energies inconsistent with those expected from the atmospheric muon and neutrino backgrounds. These properties are, however, consistent with generic predictions for an additional component of extraterrestrial origin.

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      Most cited references 22

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      High Energy Neutrinos from Cosmological Gamma-Ray Burst Fireballs

      Observations suggest that \(\gamma\)-ray bursts (GRBs) are produced by the dissipation of the kinetic energy of a relativistic fireball. We show that a large fraction, \(\ge 10%\), of the fireball energy is expected to be converted by photo-meson production to a burst of \(\sim10^{14} eV\) neutrinos. A km^2 neutrino detector would observe at least several tens of events per year correlated with GRBs, and test for neutrino properties (e.g. flavor oscillations, for which upward moving \(\tau\)'s would be a unique signature, and coupling to gravity) with an accuracy many orders of magnitude better than is currently possible.
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        Prompt neutrino fluxes from atmospheric charm

        We calculate the prompt neutrino flux from atmospheric charm production by cosmic rays, using the dipole picture in a perturbative QCD framework, which incorporates the parton saturation effects present at high energies. We compare our results with the next-to-leading order perturbative QCD result and find that saturation effects are large for neutrino energies above 10^6 GeV, leading to a substantial suppression of the prompt neutrino flux. We comment on the range of prompt neutrino fluxes due to theoretical uncertainties.
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          First observation of PeV-energy neutrinos with IceCube

          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 PeV, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current \(\nu_{e,\mu,\tau}\) (\(\bar\nu_{e,\mu,\tau}\)) or charged-current \(\nu_{e}\) (\(\bar\nu_{e}\)) interactions within the IceCube detector. The events were discovered in a search for ultra-high energy neutrinos using data corresponding to 615.9 days effective livetime. The expected number of atmospheric background is \(0.082 \pm 0.004 \text{(stat)}^{+0.041}_{-0.057} \text{(syst)}\). The probability to observe two or more candidate events under the atmospheric background-only hypothesis is \(2.9\times10^{-3}\) (\(2.8\sigma\)) 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.
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            Author and article information

            Journal
            20 November 2013
            2013-12-16
            1311.5238
            10.1126/science.1242856

            http://arxiv.org/licenses/nonexclusive-distrib/1.0/

            Custom metadata
            Science 342, 1242856 (2013)
            Revised version corrects the energy threshold for figure 7 (bottom) and one affiliation in the author list. The effective area (figure 7, top) is not affected and remains unchanged. The correction does not influence any of the results presented in the paper, and the text remains unchanged. Address correspondence to: Claudio Kopper, Naoko Kurahashi, Nathan Whitehorn
            astro-ph.HE astro-ph.CO hep-ex

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