Neutrinos

A neutrino is a lepton with no charge and a very tiny rest mass. It travels at almost the speed of light and interacts only through the weak interaction and gravity.Neutrinos were first proposed to explain beta decay. The beta particles emitted by a given nuclide have a range of kinetic energies up to a maximum, so some energy seemed to be missing. A third, neutral particle carrying away the rest of the energy and momentum saved the conservation of energy.Because they have no charge and hardly any mass, and the weak interaction has a very short range, neutrinos pass through matter almost unaffected. Billions from the Sun pass through your body every second, and huge detectors are needed to record even a few of them.There are three flavours of neutrino: the electron neutrino ν_e, the muon neutrino ν_μ and the tau neutrino ν_τ. Each has an antineutrino with the opposite lepton number.Electron neutrinos and antineutrinos are produced in beta decay: an electron antineutrino is emitted with an electron in β^- decay, and an electron neutrino with a positron in β⁺ decay. Muon neutrinos and antineutrinos come from the decays of muons and pions.