Constraints on Vacuum Oscillations from Recent Solar Neutrino Data

A detailed study of the solar neutrino vacuum oscillation was made taking into account three neutrino flavours and the seasonal effect. This analysis was established for a range of the mixing parameter sin^2(2\phi), that is concerned with the electron-tau neutrino oscillations, from 0 to 1. We obtained the allowed mass regions versus mixing angles by fitting only the rates of the five solar neutrino detectors in activity and we compared with the fits including the recoil-electron spectrum of the Kamiokande and Super-Kamiokande experiments. The averaged survival probabilities for electron neutrinos as a function of the neutrino energy are also obtained, showing that the solutions for sin^2(2\phi) greater than 0.50 with the maximum exclusion of Be7 neutrinos and the minimum exclusion of pp neutrinos give a better explanation for the suppression rates of all detectors.