lepton (redirected from leptonic)

lepton (lĕp`tŏn') [Gr.,=light (i.e., lightweight)], class of elementary particles that includes the electron and its antiparticle, the muon and its antiparticle, the tau and its antiparticle, and the neutrino and antineutrino associated with each of these particles. Leptons are the lightest class of particles having nonzero rest mass. From a technical point of view, they are defined by their behavior, being weakly interacting fermions, i.e., leptons can result from the slow decay of nuclear particles such as the neutron but do not experience a strong attraction toward the nuclear particles; they are described by the Fermi-Dirac statistics, which apply to all particles restricted by the Pauli exclusion principle. This means that two identical leptons cannot occupy the same quantum state. However, one muon and one electron are allowed to occupy the same state. The muon was originally classed as a meson because of its mass, about 200 times that of the electron, but the subsequent reclassification of particles on the basis of their behavior placed it with the electron in the lepton category. The electron and the muon are almost twins, except for their large mass difference; each is negatively charged, has a positively charged antiparticle, and has an associated neutrino and antineutrino. Separate laws govern the conservation of electron family number and of muon family number, the number being +1 for ordinary particles of either family and −1 for antiparticles (see conservation laws, in physics).

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lepton

Any member of a class of fermions that respond only to electromagnetic, weak, and gravitational forces and do not take part in strong interactions. Leptons have a half-integral spin and obey the Pauli exclusion principle. They can either carry one unit of electric charge or be neutral. The charged leptons are the electrons, muons, and taus. Each has a negative charge and a distinct mass. Each charged lepton has an associated neutral partner, or neutrino, which has no electric charge and very little if any mass.

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lepton¹

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

2. a small coin of ancient Greece

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lepton²

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

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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.

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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