PeV Tau Neutrinos to Unveil Ultra-High-Energy Sources

TL;DR

This paper proposes a novel method for Cherenkov detectors to detect EeV tau neutrinos at PeV energies, significantly enhancing the ability to identify ultra-high-energy cosmic ray sources and fluxes.

Contribution

It introduces a new technique for detecting Earth-traversing tau neutrinos at PeV energies, improving sensitivity to transient sources and diffuse fluxes.

Findings

Cherenkov detectors can improve sensitivity to transient sources by over an order of magnitude.

Sensitivity to ultra-high-energy diffuse neutrino flux can be increased by up to a factor of two.

The method enables unprecedented reach to EeV fluxes using PeV energy observations.

Abstract

The observation of ultra-high-energy EeV-energy cosmogenic neutrinos provides a direct path to identifying the sources of the highest energy cosmic rays; searches have so far resulted in only upper limits on their flux. However, with the realization of cubic-kilometer detectors such as IceCube and, in the near future, KM3NeT, GVD-Baikal, and similar instruments, we anticipate the observation of PeV-energy cosmic neutrinos with high statistics. In this context, we draw attention to the opportunity to identify EeV tau neutrinos at PeV energy using Earth-traversing tau neutrinos. We show that Cherenkov detectors can improve their sensitivity to transient point sources by more than an order of magnitude by indirectly observing EeV tau neutrinos with initial energies that are nominally beyond their reach. This new technique also improves their sensitivity to the ultra-high-energy diffuse neutrino flux by up to a factor of two. Our work exemplifies how observing tau neutrinos at PeV energies provides an unprecedented reach to EeV fluxes.