Reexamination of neutrino oscillation solutions to the solar-neutrino problem.

Abstract

A deficit of solar neutrinos compared to the standard solar model prediction has been measured in both the Homestake and Kamiokande-II experiments, with quite different detectors. We analyze the parameter space for oscillations of two neutrinos to find regions that can explain both experiments. Long-wavelength vacuum oscillation solutions are found with $\ensuremath{\delta}{m}^{2}\ensuremath{\simeq}0.5\ensuremath{-}2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ e${\mathrm{V}}^{2}$ and ${sin}^{2}2\ensuremath{\theta}\ensuremath{\gtrsim}0.7$. Matter-enhanced oscillation solutions are found for (i) nonadiabatic transitions having $\ensuremath{\delta}{m}^{2}{\ensuremath{\theta}}^{2}\ensuremath{\approx}{10}^{\ensuremath{-}8}$ e${\mathrm{V}}^{2}$ and $\ensuremath{\delta}{m}^{2}\ensuremath{\approx}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ e${\mathrm{V}}^{2}$, and (ii) adiabatic transitions having $\ensuremath{\delta}{m}^{2}\ensuremath{\approx}{10}^{\ensuremath{-}7}\ensuremath{-}{10}^{\ensuremath{-}4}$ e${\mathrm{V}}^{2}$ with ${sin}^{2}2\ensuremath{\theta}\ensuremath{\gtrsim}0.5$. The two-neutrino long-wavelength and matter-enhanced solutions predict $^{71}\mathrm{Ga}$ measurements in the ranges 50-80 and 5-115 solar-neutrino units (SNU), respectively, compared to 130 SNU without oscillations. We emphasize the distinctive features of each solution, including their predictions for future $\ensuremath{\nu}\ensuremath{-}e$ scattering experiments and detectable seasonal variations in the long-wavelength solutions. We also find the range of three-neutrino vacuum oscillation solutions.