lepton

lepton

¹

1. a former Greek monetary unit worth one hundredth of a drachma

2. a small coin of ancient Greece

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lepton

²

Physics any of a group of elementary particles and their antiparticles, such as an electron, muon, or neutrino, that participate in electromagnetic and weak interactions and have a half-integral spin

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Lepton

An elementary particle having no internal constituents which interacts through the electromagnetic, weak, and gravitational forces, but does not interact through the strong (nuclear) force. Leptons are very small, less than 10^-18 m in size. This is less than 10^-3 the size of a nucleus and less than 10^-8 the size of an atom. Indeed, existing measurements are consistent with leptons being point particles.

These properties of the lepton family of particles are to be contrasted with the properties of the quark family of particles. Quarks interact through the strong force as well as through the electromagnetic, weak, and gravitational forces. By means of the strong force, quark-antiquark pairs bind together to form hadrons such as the &pgr; meson, and the quarks bind together to form hadrons such as the proton. In contrast, leptons act as individual particles and can be studied as isolated particles whereas, as far as is known, quarks are always inside hadrons and cannot be studied as isolated particles. See Fundamental interactions, Hadron, Quarks

Six leptons are known. There are three known charged leptons: the electron (e), muon (μ), and tau (&tgr;). Associated with each charged lepton is a neutral lepton called a neutrino. A charged lepton and its associated neutrino is said to form a lepton generation. Thus there are three known lepton generations. See Electron, Neutrino

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

lepton

[′lep‚tän]

(particle physics)

A fermion having a mass smaller than the proton mass; leptons interact with electromagnetic and gravitational fields, but beyond this they interact only through weak interactions.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.