Observation of Seven Astrophysical Tau Neutrino Candidates with IceCube

We report on a measurement of astrophysical tau neutrinos with 9.7 years of IceCube data. Using convolutional neural networks trained on images derived from simulated events, seven candidate ${\nu }_{\tau }$ events were found with visible energies ranging from roughly 20 TeV to 1 PeV and a median expected parent ${\nu }_{\tau }$ energy of about 200 TeV. Considering backgrounds from astrophysical and atmospheric neutrinos, and muons from ${\pi }^{\pm }\mathrm{/}{K}^{\pm }$ decays in atmospheric air showers, we obtain a total estimated background of about 0.5 events, dominated by non-${\nu }_{\tau }$ astrophysical neutrinos. Thus, we rule out the absence of astrophysical ${\nu }_{\tau }$ at the $5\sigma$ level. The measured astrophysical ${\nu }_{\tau }$ flux is consistent with expectations based on previously published IceCube astrophysical neutrino flux measurements and neutrino oscillations.