lepton (lĕp`tŏn') [Gr.,=light (i.e., lightweight)], class of elementary particles elementary particles, the most basic physical constituents of the universe.

Basic Constituents of Matter

Molecules are built up from the atom , which is the basic unit of any chemical element .
..... Click the link for more information. that includes the electron electron, elementary particle carrying a unit charge of negative electricity. Ordinary electric current is the flow of electrons through a wire conductor (see electricity ). The electron is one of the basic constituents of matter.
..... Click the link for more information. and its antiparticle antimatter, composed of atoms made up of antiprotons and antineutrons in a nucleus surrounded by positrons. A very simple type of "atom" incorporating antiparticles is positronium, a brief pairing of a positron and an electron that may occur before their annihilation.
..... Click the link for more information. , the muon muon (my
..... Click the link for more information. and its antiparticle, the tau and its antiparticle, and the neutrino neutrino (n

trē`nō) [Ital.
..... Click the link for more information. 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 exclusion principle, physical principle enunciated by Wolfgang Pauli in 1925 stating that no two electrons in an atom can occupy the same energy state simultaneously.
..... Click the link for more information. . 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 meson (mē`zŏn) [Gr.,=middle (i.e.
..... Click the link for more information. 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 conservation laws, in physics, basic laws that together determine which processes can or cannot occur in nature; each law maintains that the total value of the quantity governed by that law, e.g., mass or energy, remains unchanged during physical processes.
..... Click the link for more information. , in physics).

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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Basic Constituents of Matter

lepton

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