Lepton << LEHP ton >> is one of the three major families of elementary particles. The other families are quarks and bosons. Most physicists believe leptons are fundamental units of matter—that is, the particles do not consist of smaller units.
Physicists have identified six types of leptons—electrons, muons, taus, and three kinds of neutrinos. Electrons, muons, and taus have a negative electric charge. Muons and taus have a much larger mass than that of electrons. A muon is about 207 times as heavy as an electron, and a tau is 3,477 times as heavy. No difference has been found between electrons, muons, and taus other than their mass.
The three kinds of neutrinos have no electric charge. They are called electron-, muon-, and tau-neutrinos because each is associated with one type of charged lepton. Their mass has so far proved to be too small to measure.
All leptons have antimatter counterparts that are called antileptons. Antileptons have the same mass as leptons, but all the other properties are reversed. Because neutrinos have no charge, their antiparticles also are neutral.
Muons and taus are unstable particles, and so they decay (break down) into lighter particles. A muon decays into an electron, a muon-neutrino, and an electron-antineutrino in about 2 millionths of a second. The lifetime of a tau is less than 2 trillionths of a second. A tau, because of its large mass, can decay into many different combinations of lighter particles.
See also Antimatter; Muon; Neutrino.
