Measurement of Astrophysical Tau Neutrinos in IceCube's High-Energy Starting Events

Abstract

We present the results of a search for astrophysical tau neutrinos in 7.5 years of IceCube's high-energy starting event data. At high energies, two energy depositions stemming from the tau neutrino charged-current interaction and subsequent tau lepton decay may be resolved. We report the first detection of two such events, with probabilities of $\sim 76\%$ and $\sim 98\%$ of being produced by astrophysical tau neutrinos. The resultant astrophysical neutrino flavor measurement is consistent with expectations, disfavoring a no-astrophysical tau neutrino flux scenario with 2.8$\sigma$ significance.Comment: This article is supported by a long-form paper that discusses the high-energy starting event selection titled: "The IceCube high-energy starting event sample: Description and flux characterization with 7.5 years of data.