Feasibility of Determining Diffuse Ultra-High Energy Cosmic Neutrino Flavor Ratio through ARA Neutrino Observatory

TL;DR

This study assesses the potential of the ARA Neutrino Observatory to determine the flavor ratio of ultra-high energy cosmic neutrinos by analyzing the angular distribution of detected events, considering neutrino oscillations and decay scenarios.

Contribution

The paper demonstrates, through simulations, that the ARA Observatory can feasibly constrain the UHECN flavor ratio using event-direction distributions and probabilistic analysis.

Findings

Feasibility of flavor ratio determination with ARA

Dependence of accuracy on number of events and angular resolution

Potential to distinguish neutrino physics scenarios

Abstract

The flavor composition of ultra-high energy cosmic neutrinos (UHECN) carries precious information about the physical properties of their sources, the nature of neutrino oscillations and possible exotic physics involved during the propagation. Since UHECN with different incoming directions would propagate through different amounts of matter in Earth and since different flavors of charged leptons produced in the neutrino-nucleon charged-current (CC) interaction would have different energy-loss behaviors in the medium, measurement of the angular distribution of incoming events by a neutrino observatory can in principle be employed to help determine the UHECN flavor ratio. In this paper we report on our investigation of the feasibility of such an attempt. Simulations were performed, where the detector configuration was based on the proposed Askaryan Radio Array (ARA) Observatory at the South Pole, to investigate the expected event-direction distribution for each flavor. Assuming $\nu_{\mu}$-$\nu_{\tau}$ symmetry and invoking the standard oscillation and the neutrino decay scenarios, the probability distribution functions (PDF) of the event directions are utilized to extract the flavor ratio of cosmogenic neutrinos on Earth. The simulation results are summarized in terms of the probability of flavor ratio extraction and resolution as functions of the number of observed events and the angular resolution of neutrino directions. We show that it is feasible to constrain the UHECN flavor ratio using the proposed ARA Observatory.