Astronomy   View all facts   Glossary   Help

physical object > natural object > particle > elementary particle > lepton

lepton
subject			fact

lepton	has spin 1/2
	has definition A fermion which is not made of quarks.
	has definition The generic name for any spin-1/2 particle which does not feel the strong nuclear force. The six known leptons are the electron, the muon, the tau lepton, and their respective neutrinos. The name was originally coined to refer to light particles.
	has definition Any fermion that does not participate in the strong interactions. Leptons include the electron family and the muon family.
	has definition Elementary particle that does not participate in the strong interactions, including electrons, muons, and neutrinos.
	has definition Elementary particle that have no measurable size and are not influenced by the strong nuclear force. Electrons, muons, and neutrinos are leptons.
	has definition A class of non-strongly-interacting particles that includes the electron, muon, tau, and their associated neutrinos. See Table 7.1 on page 120.
	has definition A fundamental particle of nature, which may interact via all of the fundamental forces except the strong nuclear force. The electron is an example of a lepton.
	has definition Elementary particle like the electron and neutrino that do not experience the strong nuclear force. Unlike the strongly interacting hadrons, the leptons have small masses.
	is a kind of fermion
	is a kind of elementary particle
fermion	has quantum behavior Fermi-Dirac statistics
	obeys exclusion principle
particle	has frequency inversely proportional to the wavelength
	has wavelength inversely proportional to its momentum
	has charge
	has mass
physical object	has location or center of gravity
	has angular momentum
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material

Kinds of lepton :

• antineutrino (5 facts) - The antiparticle of a neutrino.
• electron (9 kinds, 35 facts) - Negatively charged fundamental particle (also called a beta particle) found in the atoms of all elements, where it "orbits" (at different energy levels and with different directions of spin) round the central nucleus. The combined charge of the orbiting electrons is balanced (in a neutral atom) by the charge of an equal number of positively charged protons in the atomic nucleus. An electron is also the fundamental unit of electricity., A small, negatively charged particle that appears in every neutral atom, surrounding the positively charged nucleus like bees around honey., A negatively charged spin-1/2 particle, which interacts via the electromagnetic, weak and gravitational forces. It has a mass of 0.511 MeV / c², some 1800 times lighter than the proton., A lepton with an electric charge of -1. An electron is also a fermion because it has a spin of one half., A stable, negatively charged elementary particle - the lightest massive particle known. The classical electron radius is 2.82 × 10^-13 cm; m_e = 9.1 × 10^-28 g = 5.48597 × 10^-4 amu. The electron family (see lepton) includes the electron e^-, the positron e⁺, the electron neutrino ν_e, and the electron antineutrino ν_ebar. Rest-mass energy of electron 8.186 × 10^-7 ergs. Electron charge = 1.60219 × 10^-19 coulombs., Light elementary particle with a negative electrical charge. Electrons are found in shells surrounding the nuclei of atoms; their interactions with the electrons of neighboring atoms create the chemical bonds that link atoms together as molecules.
• muon (9 facts) (μ) - A second-generation lepton. It is essentially a more massive electron., Short-lived elementary particle with negative electrical charge. Muons are leptons. They resemble electrons, but are 207 times more massive., An elementary particle, formerly called a mu-meson but now classified with the leptons because it seems to be identical with the electron except for its much greater mass (207 times that of an electron). The muon family includes the muons and their neutrinos (and their antiparticles). Muons may have a positive or a negative charge., Elementary particles produced when cosmic rays enter the upper atmosphere.
• neutrino (9 facts) - An electrically neutral, very weakly interacting particle, with a rest energy which is either zero or very small. The particle was predicted in 1931 as a means of reconciling the measurements of beta decays with the conservation of energy, but it was not directly detected until 1956., Chargeless species of particle, subject only to the weak force., An electrically neutral, massless particle of spin-1/2, which interacts only by the weak force and gravity. It was first postulated by Pauli in 1930 to ensure conservation of energy and angular momentum in nuclear β decay. Three different types of neutrinos are known to exist corresponding to the three massive leptons: ν_e, ν_µ and ν _τ., A fundamental elementary particle with no electric charge and very small if any rest mass. Believed to be exceedingly abundant in the universe. The neutrino has a very low cross-section for interaction with matter and is almost impossible to detect, hence the uncertainty over its rest mass. The Sun produces neutrinos from thermonuclear reactions in its core, and a large flux of neutrinos carries away most of the energy, of a supernova. Neutrinos are one candidate for Dark Matter. Experiments to detect cosmic neutrinos involve large masses of "stopping" material and indirect detection of the effects of neutrino absorption., A stable particle with no charge, a rest mass of zero, and a spin of 1/2, that carries away energy in the course of nuclear reactions. Its main characteristic is the weakness of its interactions with all other particles. Since the wavelengths of neutrinos at the energies at which they are normally emitted from unstable nuclei are only a few thousandths of an angstrom (compared with the wavelength of a light photon which is several thousand angstroms), they have negligible probability (10^-19 that of a light photon) of interacting with matter and escape at the speed of light. Neutrinos arise only in the energy-producing regions of stars and therefore, unlike light photons, provide direct evidence of conditions in stellar cores. There are two types of neutrinos, those associated with electrons (v_e) and those associated with muons (v_µ).
• positron (10 facts) (antielectron) - The antiparticle of the electron, discovered by Anderson in 1934. It has the same mass and spin as the electron, but opposite charge and magnetic moment.
• tau (5 facts) (τ)

Next elementary particle: parton    Up: elementary particle, fermion    Previous elementary particle: hadron