How astrophysical neutrino sources could be used for early measurements of neutrino mass hierarchy and leptonic CP phase

Abstract

We discuss the possible impact of astrophysical neutrino flux measurements at neutrino telescopes on the neutrino oscillation program of reactor experiments and neutrino beams. We consider neutrino fluxes from neutron sources, muon damped sources, and pion sources, where we parameterize the input from these sources in terms of the flux ratio $R=ϕ_μ/(ϕ_e+ϕ_τ)$ which can be extracted from the muon track to shower ratio in a neutrino telescope. While it is difficult to obtain any information from this ratio alone, we demonstrate that the dependence on the oscillation parameters is very complementary to the one of reactor experiments and neutrino beams. We find that for large values of $\sin^2 2 θ_{13}$, a measurement of R with a precision of about 20% or better may not only improve the measurement of the leptonic CP phase, but also help the determination of the mass hierarchy. In some cases, early information on $δ_{CP}$ may even be obtained from Double Chooz and an astrophysical flux alone without the help of superbeams. For small values of $\sin^2 2 θ_{13}$, we find that using the information from an astrophysical neutrino flux could eliminate the octant degeneracy better than reactor experiments and beams alone. Finally, we demonstrate that implementing an additional observable based on the electromagnetic to hadronic shower ratio at a neutrino telescope (such as at higher energies) could be especially beneficial for pion beam sources.