Determination of the Source Flavor Ratio of Ultrahigh Energy Neutrinos

TL;DR

This paper explores methods to reconstruct the initial flavor composition of ultrahigh energy neutrinos from distant sources, emphasizing flavor discrimination challenges and the impact of neutrino mixing uncertainties on source flavor ratio determination.

Contribution

It introduces a flavor ratio reconstruction approach considering current measurement accuracies and neutrino mixing uncertainties, highlighting the difficulty in separating muon and tau neutrino events at very high energies.

Findings

Flavor ratio can be reconstructed with current detector accuracies.

Separation of  and  neutrinos is feasible via shower signatures.

Distinguishing  from  neutrinos is possible, but  and  separation does not improve reconstruction.

Abstract

We discuss the reconstruction of neutrino flavor neutrino at a distant source in the very high en- ergy regime. This reconstruction procedure is relevant to the confirmation of detecting cosmogenic neutrinos, for example. To facilitate such a reconstruction, it is imperative to achieve effective flavor discriminations in terrestrial neutrino telescopes. We note that, for energies beyond few tens of PeV, a tau-lepton behaves like a track similar to a muon. Hence, while it is rather challenging to separate {\nu}{\mu} from {\nu}{\tau} in this case, one can expect to isolate {\nu}e from the rest by a distinctive shower signature. We present the result of flavor ratio reconstruction given the anticipated accuracies of flavor measurement in neutrino telescopes and current uncertainties of neutrino mixing parame- ters. It is shown that the further separation between {\nu}{\mu} and {\nu}{\tau} events does not improve the flavor reconstruction due to the approximate {\nu}{\mu} - {\nu}{\tau} symmetry.