Abstract
The long baseline between the Earth and the Sun makes solar neutrinos an excellent test beam for exploring possible neutrino decay. The signature of such decay would be an energy-dependent distortion of the traditional survival probability which can be fit for using well-developed and high precision analysis methods. Here a model including neutrino decay is fit to all three phases of $^8$B solar neutrino data taken by the Sudbury Neutrino Observatory. This fit constrains the lifetime of neutrino mass state $\nu_2$ to be ${>8.08\times10^{-5}}$ s/eV at $90\%$ confidence. An analysis combining this SNO result with those from other solar neutrino experiments results in a combined limit for the lifetime of mass state $\nu_2$ of ${>1.04\times10^{-3}}$ s/eV at $99\%$ confidence.
Highlights
Nuclear reactions in the core of the Sun produce electron flavor neutrinos at rates which can be predicted by solar models
The likelihood profile incorporating systematic uncertainties is generated by assuming the shape of the likelihood profile does not change as the systematic parameters vary, but rather shifts according to the shift in the fitted value of k2 from the shift-and-refit method
A shallow minimum at 3.45þ−15..6580 × 10−4 s=eV is found, the upper uncertainty is consistent with infinite lifetime at confidences greater than 85%, meaning this analysis is not a significant measurement of neutrino decay
Summary
Nuclear reactions in the core of the Sun produce electron flavor neutrinos at rates which can be predicted by solar models. The previously published fits assumed the total flux was conserved, i.e., they inferred Pea, the probability of detecting a solar neutrino as a νμ or ντ neutrino at Earth, from the constraint Pee þ Pea 1⁄4 1 which does not apply in a decaying scenario Both points are addressed in this analysis by implementing and fitting to a model including neutrino decay that independently calculates Pee and Pea. Precise measurements of neutrino mixing parameters from KamLAND [6] and Daya Bay [20] along with improved theoretical predictions for the 8B flux [21] reduce the uncertainty in the underlying solar neutrino model.
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