Concept and Analysis for a 1 – 100 PeV Tau Neutrino Observatory

The IceCube Neutrino observatory has discovered an astrophysical neutrino flux in the energy range $>$1~TeV with their highest energy event $\sim$3~PeV. Although IceCube has excellent muon flavor identification, their ability to identify tau neutrinos is highly limited. We present a concept for observing the tau neutrino flux in the 1--100 PeV range, where a flux is guaranteed and its observation would give further support to the astrophysical origin of the IceCube flux. The design of the observatory requires an acceptance $\langle A\Omega\rangle >$400~m$^2$~sr$\times\left(\frac{E}{\mathrm{PeV}}\right)^{1.5}$ to match the $\sim$1~PeV IceCube all-flavor event rate in tau neutrinos provided a $\nu_e:\nu_\mu:\nu_\tau = 1:1:1$ flavor ratio. The energy dependence of the acceptance is designed to match the IceCube best-fit spectral flux index of $E^{-2.5}$ so the spectrum is evenly sampled in the 1--100 PeV range. We present a background-free implementation with pointing resolution $<1^\circ$ to begin the era of high energy tau neutrino astronomy.