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Encyclopedia > Lepton

In physics, a lepton is a sub-atomic particle with spin of 1/2 that does not experience the strong interaction (that is, the strong nuclear force). The leptons form a family of fermions that are distinct from the other known family of fermions, the quarks. ISO 4217 Code GRD User(s) Greece Inflation 3. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... Fermions, named after Enrico Fermi, are particles which form totally-antisymmetric composite quantum states. ... For other uses, see Quark (disambiguation). ...

Contents

There are three known flavors of lepton: the electron, the muon, and the tau lepton or tau (or sometimes tauon). Each flavor is represented by a pair of particles called a weak doublet. One is a massive charged particle that bears the same name as its flavor (like the electron). The other is a nearly massless neutral particle called a neutrino (such as the electron neutrino). All six of these particles have corresponding antiparticles (such as the positron or the electron antineutrino). All known charged leptons have a single unit of negative or positive electric charge (depending on whether they are particles or antiparticles) and all of the neutrinos and antineutrinos have zero electric charge. The charged leptons have two possible spin states, while only one helicity is observed for the neutrinos (all the neutrinos are left-handed, and all the antineutrinos are right-handed). Flavour (or flavor) is a quantum number of elementary particles related to their weak interactions. ... For other uses, see Electron (disambiguation). ... The muon (from the letter mu (Î¼)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. ... The tau lepton (often called the tau, tau particle, or occasionally the tauon, symbol ) is a negatively charged elementary particle with a lifetime of 2. ... The tau lepton (often called the tau, tau particle, or occasionally the tauon, symbol ) is a negatively charged elementary particle with a lifetime of 2. ... The weak isospin in theoretical physics parallels the idea of the isospin under the strong interaction, but applied under the weak interaction. ... For other uses, see Electron (disambiguation). ... For other uses, see Neutrino (disambiguation). ... The neutrino is an elementary particle. ... Corresponding to most kinds of particle, there is an associated antiparticle with the same mass and opposite charges. ... The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ... An antineutrino is the antimatter equivalent particle of the neutrino. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... In particle physics, helicity is the projection of the angular momentum to the direction of motion: Because the angular momentum with respect to an axis has discrete values, helicity is discrete, too. ... In particle physics, helicity is the projection of the angular momentum to the direction of motion: Because the angular momentum with respect to an axis has discrete values, helicity is discrete, too. ... In particle physics, helicity is the projection of the angular momentum to the direction of motion: Because the angular momentum with respect to an axis has discrete values, helicity is discrete, too. ...

The masses of the leptons also obey a simple relation, known as the Koide formula, but at present this relationship cannot be explained. This unexplained relation was discovered by Yoshio Koide in 1981, and relates the masses of the three leptons so well that it predicted the mass of the tau lepton. ...

When particles interact, generally the number of leptons of the same type (electrons and electron neutrinos, muons and muon neutrinos, tau leptons and tau neutrinos) remains the same. This principle is known as conservation of lepton number. Conservation of the number of leptons of different flavors (for example, electron number or muon number) may sometimes be violated (as in neutrino oscillation). A much stronger conservation law is the total number of leptons of all flavors, which is violated by a tiny amount in the Standard Model by the so-called chiral anomaly. In high energy physics, the lepton number is the number of leptons minus the number of antileptons. ... Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... A chiral anomaly is the anomalous nonconservation of a chiral current. ...

The couplings of the leptons to gauge bosons are flavor-independent. This property is called lepton universality and has been tested in measurements of the tau and muon lifetimes and of Z-boson partial decay widths, particularly at the Stanford Linear Collider and Large Electron-Positron Collider(LEP) experiments. Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... Given an assembly of elements, the number of which decreases ultimately to zero, the lifetime (also called the mean lifetime) is a certain number that characterizes the rate of reduction (decay) of the assembly. ... The Stanford Linear Collider was a linear accelerator that collided electrons and positrons at the Stanford Linear Accelerator Center. ... The LEP tunnel at CERN, now being filled with magnets for the LHC The Large Electron-Positron Collider (LEP) is one of the largest particle accelerators finished so far. ...

Table of the leptons

Name Symbol Electric charge (e) Mass (MeV/c2) Name Symbol Electric charge (e) Mass (MeV/c2) Charged lepton / antiparticle Neutrino / antineutrino Electron / Positron e−/e+ −1 / +1 0.511 Electron neutrino / Electron antineutrino νe/νe 0 < 0.0000022 [1] Muon μ−/μ+ −1 / +1 105.7 Muon neutrino / Muon antineutrino νμ/νμ 0 < 0.17 [1] Tau lepton τ−/τ+ −1 / +1 1777 Tau neutrino / Tau antineutrino ντ/ντ 0 < 15.5 [1]

Note that the neutrino masses are known to be non-zero because of neutrino oscillation, but their masses are sufficiently light that they have not been measured directly as of 2008. However there have been measured (indirectly based on the oscillation periods) the differences of the mass squares between the neutrinos, which have been estimated $Delta m^2_{12} = 80{meV}^2$ and $Delta m^2_{23} approx Delta m^2_{13} = 2400{meV}^2$. This leads to the following conclusions: The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... The elementary charge (symbol e or sometimes q) is the electric charge carried by a single proton, or equivalently, the negative of the electric charge carried by a single electron. ... For other uses, see Electron (disambiguation). ... The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ... For other uses, see Electron (disambiguation). ... The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ... For other uses, see Neutrino (disambiguation). ... Antineutrinos, the antiparticles of neutrinos, are neutral particles produced in nuclear beta decay. ... The neutrino is an elementary particle. ... An antineutrino is the antimatter equivalent particle of the neutrino. ... The muon (from the letter mu (Î¼)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. ... The muon (from the letter mu (Î¼)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. ... An antimuon is the antiparticle of the muon. ... The neutrino is an elementary particle. ... An antineutrino is the antimatter equivalent particle of the neutrino. ... The tau lepton (often called the tau, tau particle, or occasionally the tauon, symbol ) is a negatively charged elementary particle with a lifetime of 2. ... The tau lepton (often called the tau, tau particle, or occasionally the tauon, symbol ) is a negatively charged elementary particle with a lifetime of 2. ... An antitauon is the antiparticle of the tauon. ... The neutrino is an elementary particle. ... An antineutrino is the antimatter equivalent particle of the neutrino. ... Neutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvo whereby a neutrino created with a specific lepton flavor (electron, muon or tau) can later be measured to have a different flavor. ...

• νμ and ντ are lighter than 2.2 eV (as νe is and the mass differences between the neutrinos are of order of millielectronvolts)
• one (or more) of the neutrinos is heavier than 0.040 eV
• two (or three) of the neutrinos are heavier than 0.008 eV

The names "mu" and "tau" seem to have been selected due to their places in the Greek alphabet; μ is seven letters after ε, whereas τ is seven letters after μ. This page contains special characters. ...

Etymology

According to the Oxford English Dictionary, the name "lepton" (from Greek leptos meaning 'thin') was first used by physicist Léon Rosenfeld in 1948: The Oxford English Dictionary print set The Oxford English Dictionary (OED) is a dictionary published by the Oxford University Press (OUP), and is the most successful dictionary of the English language, (not to be confused with the one-volume Oxford Dictionary of English, formerly New Oxford Dictionary of English, of... Belgian physicist. ...

Following a suggestion of Prof. C. Møller, I adopt — as a pendant to "nucleon" — the denomination "lepton" (from λεπτός, small, thin, delicate) to denote a particle of small mass.

[2]

The name originates from before the discovery in the 1970s of the heavy tau lepton, which is nearly twice the mass of a proton. For other uses, see Proton (disambiguation). ...

This is a list of particles in particle physics, including currently known and hypothetical elementary particles, as well as the composite particles that can be built up from them. ...

References

1. ^ a b c Laboratory measurements and limits for neutrino properties.
2. ^ Rosenfeld, Léon (1948). Nuclear Forces. Interscience Publishers, New York, xvii.

Results from FactBites:

 Lepton - Wikipedia, the free encyclopedia (229 words) The leptons form a family of elementary particles that are distinct from the gauge bosons and the quarks. 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. Leptons from the Georgia State University is a small summary of the Lepton.
 Lepton (currency) - Wikipedia, the free encyclopedia (135 words) Lepton pl. Lepta (Λεπτόν pl. Λεπτά) is the name of various fractional units of currency used in the Greek-speaking world from antiquity until today. The Roman mite was informally called lepton in the Greek-speaking parts of the Roman Empire; this use is seen in the New Testament. In modern Greece, lepton (modern form: lepto, Λεπτό) is the name of the 1/100 denomination of all the official currencies of the Greek state: The Phoenix (1827-1832), the Drachma (1832-2001) and the Euro (2002-current).
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