The Online Encyclopedia and Dictionary







A lepton is also a unit of currency.

In physics, a particle is a lepton if it has a spin of 1/2 and does not experience the strong nuclear force. The leptons form a family of elementary particles that are distinct from the gauge bosons and the quarks.

The name "lepton" comes from the Greek λεπτόν, meaning "small" or "thin". However, this name originates from before the discovery of a particularly heavy lepton called the tauon. The tauon is nearly twice the mass of a proton.

There are 12 known types of lepton, 3 of which are matter particles (the electron, the muon and the tauon), 3 corresponding neutrinos, and their 6 respective antiparticles. All known charged leptons have a single negative or positive electric charge (depending on whether they are particles or antiparticles) and all of the neutrinos and antineutrinos have neutral electric charge. In general, the number of leptons of the same type (electrons and electron neutrinos; muons and muon neutrinos; tauons and tau neutrinos) remains the same when particles interact (known as conservation of lepton number).

A table of the leptons

Charged particle / antiparticle Neutrino / antineutrino
Name Symbol Electric charge Mass(GeV) Name Symbol Electric charge Mass(MeV)
Electron / Antielectron (positron) e^- \, / \, e^+ −1 / +1 0.000511 Electron neutrino / Electron antineutrino \nu_e \, / \, \overline{\nu}_e 0 <0.000003
Muon / Antimuon \mu^- \, / \, \mu^+ −1 / +1 0.1056 Muon neutrino / Muon antineutrino \nu_\mu \, / \, \overline{\nu}_\mu 0 <0.19
Tauon / Antitauon \tau^- \, / \, \tau^+ −1 / +1 1.777 Tau neutrino / Tau antineutrino \nu_\tau \, / \, \overline{\nu}_\tau 0 <18.2

See also

External links

Last updated: 05-06-2005 14:21:35