| Summary: | IceCube is an all-flavor, cubic kilometer neutrino telescope currently under constructionin the deep glacial ice at the South Pole. Its embedded optical sensors detect Cherenkovlight from charged particles produced in neutrino interactions in the ice. For several yearsIceCube has been detecting muon tracks from charged-current muon neutrino interactions.However, IceCube has yet to observe the electromagnetic or hadronic particle showers or"cascades" initiated by charged-current or neutral-current neutrino interactions. The firstdetection of such an event signature is expected to come from the known flux of atmosphericelectron and muon neutrinos.A search for atmospheric neutrino-induced cascades was performed using 275.46days of data from IceCube's 22-string configuration. Reconstruction and background rejectiontechniques were developed to reach, for the first time, a signal-to-background ratio~1. Above a reconstructed energy of 5 TeV, 12 candidate events were observed in the fulldataset. The signal expectation from the canonical Bartol atmospheric neutrino flux modelis 5.63 +- 2.25 events, while the expectation from the atmospheric neutrino flux as measuredby IceCube's predecessor array AMANDA is 7.48 +- 1.50 events. Quoted errors include theuncertainty on the flux only.While a conclusive detection can not yet be claimed because of a lack of backgroundMonte Carlo statistics, the evidence that we are at the level of background suppressionneeded to see atmospheric neutrino-induced cascades is strong. In addition, one extremelyinteresting candidate event of energy 133 TeV survives all cuts and shows an intriguingdouble pulse structure in its waveforms that may signal the "double bang" of a tau neutrinointeraction.
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