Possible Explanation of the Solar-Neutrino Puzzle

Mikheyev and Smirnov have shown that electron neutrinos above a certain minimum energy $E_m$ may all be converted into $\mu$ neutrinos on their way out through the sun. We assume here that this is the reason why Davis and collaborators, in their experiments, find many fewer solar neutrinos than predicted. The minimum energy $E_m$ is found to be about 6 MeV, the mass $m$ of the $\mu$ neutrino must be greater than that of the electron neutrino, $m_2^2-m_1^2=6\mathrm{}\times {10}^{-5\mathrm{}}$ ${\mathrm{eV}}^2$, and there is a very minor restriction on the neutrino mixing angle.