Oscillations of very low energy atmospheric neutrinos

TL;DR

This paper analyzes low-energy atmospheric neutrino oscillations below 100 MeV, deriving formulas for oscillation probabilities, and studies how mixing angles and CP-violation affect detected event spectra, aiding future large-scale experiments.

Contribution

It provides analytical expressions for oscillation probabilities of sub-100 MeV neutrinos and explores their impact on event spectra in water Cherenkov detectors.

Findings

Variation in 2-3 mixing angle affects event counts by 15-20%.

1-3 mixing and CP-violation induce ~10% changes.

Energy spectra are sensitive to mixing parameters.

Abstract

There are several new features in production, oscillations and detection of the atmospheric neutrinos of low energies, E<100 MeV. The flavor ratio, r, of muon to electron neutrino fluxes is substantially smaller than 2 and decreases with energy, significant part of events is due to the decay of invisible muons at rest, etc. Oscillations in two-layer medium (atmosphere - earth) should be taken into account. We derive analytical and semi-analytical expressions for the oscillation probabilities of these "sub-subGeV" neutrinos. The energy spectra of the e-like events in water cherenkov detectors are computed and dependence of the spectra on the 2-3 mixing angle, the 1-3 mixing and CP-violation phase are studied. We find that variations of 2-3 mixing angle in the presently allowed region change the number of e-like events by about 15 - 20 % as well as to distortion of the energy spectrum. The 1-3 mixing and CP-violation can lead to ~10% effects. Detailed study of the sub-subGeV neutrinos will be possible in future Megaton-scale detectors.