Vacuum Oscillations and Future Solar Neutrino Experiments

Abstract

Vacuum oscillations are considered for the combined solar neutrino observations, including the Kamiokande II spectrum data and incorporating theoretical uncertainties and their correlations. Despite the conceptual difficulty of the fine tuning between the neutrino parameters and the Sun-Earth distance, 2-flavor vacuum oscillations provide phenomenologically acceptable solutions. There are allowed regions at 99\% C.L. for $\Delta m^2 = (0.45 - 1.2) \times 10^{-10} \; \mbox{eV}\,^2$ and $\sin^22\theta = 0.6 - 1$; the best fit solution is $\chi^2 / \mbox{d.f.} = 19.2 / 16$, which is acceptable at 16\% C.L. Oscillations for sterile neutrinos are, however, excluded by the averaged data at 99.4\% C.L. The vacuum oscillation solutions predict characteristic energy spectrum distortions and seasonal variations in Sudbury Neutrino Observatory, Super-Kamiokande, and BOREXINO. Those predictions are given in detail, emphasizing that the vacuum solutions are distinguishable from the MSW solutions.