Neutrino

A neutral lepton; one exists for each of the charged leptons (electron, muon, and tau) all of which are very light and could possibly have zero mass. Neutrinos participate only in weak and gravitational interactions and are therefore very difficult to detect. Neutrinos are created in energetic collisions between nuclear particles. The universe is filled with them but they rarely collide with anything. Neutrinos only have a small mass but they are very numerous and may account for some of the dark matter in the Universe.

The existence of the neutrino was postulated by Enrico Fermi to explain a loss of energy in the radioactive beta decay. The neutrinos produced in the beta decay carry away the lost energy.

See also: Electron, Lepton, Muon.