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Encyclopedia > Tau lepton
Tau Lepton
Composition Elementary particle
Family Fermion
Group Lepton
Generation Third
Interaction Gravity, Electromagnetic,
Weak
Antiparticle Antitauon
Mass 1776.99±0.29 MeV/c2
Electric charge −1 e
Color charge None
Spin ½
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The tau lepton (often called the tau, tau particle, or occasionally the tauon, symbol ) is a negatively charged elementary particle with a lifetime of 2.90×10−13 seconds and a mass of 1777 MeV/c2 (compared to 938 MeV/c2 for protons and 0.511 MeV/c2 for electrons). It has an associated antiparticle (the anti-tau) and neutrinos (the tau neutrino and tau antineutrino). For the novel, see The Elementary Particles. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... In physics, a lepton is a particle with spin-1/2 (a fermion) that does not experience the strong interaction (that is, the strong nuclear force). ... In particle physics, a generation is a division of the elementary particles. ... A fundamental interaction or fundamental force is a mechanism by which particles interact with each other, and which cannot be explained in terms of another interaction. ... Gravity is a force of attraction that acts between bodies that have mass. ... Electromagnetic interaction is a fundamental force of nature and is felt by charged leptons and quarks. ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ... Corresponding to most kinds of particle, there is an associated antiparticle with the same mass and opposite charges. ... The invariant mass or intrinsic mass or proper mass or just mass is a measurement or calculation of the mass of an object that is the same for all frames of reference. ... An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... 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. ... In quantum chromodynamics (QCD), color or color charge refers to a certain property of the subatomic particles called quarks. ... 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. ... For the novel, see The Elementary Particles. ... For other uses, see Mass (disambiguation). ... An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... For other uses, see Proton (disambiguation). ... For other uses, see Electron (disambiguation). ... For other senses of this term, see antimatter (disambiguation). ... The neutrino is an elementary particle. ... An antineutrino is the antimatter equivalent particle of the neutrino. ...

Contents

Classification

The tau lepton belongs to the 3rd generation of leptons. It is the third generation counterpart of the electron (1st generation) and the muon (2nd generation). Like the electron and muon, the tau lepton appears to be pointlike; no structure has been detected, and if there is any, it would have to be on a scale of less than 10−18 meters. Also, like the electron and muon, the tau has a spin of 1/2. The tau lepton and its antiparticle carry the same electric charges as the electron and positron, respectively. In particle physics, a generation is a division of the elementary particles. ... In physics, a lepton is a particle with spin-1/2 (a fermion) that does not experience the strong interaction (that is, the strong nuclear force). ... For other uses, see Electron (disambiguation). ... The muon (from the letter mu (μ)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. ... 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 first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ...


Decay

The tau is the only lepton that can decay into hadrons—the other leptons do not have the necessary mass. Like the other decay modes of the tau lepton, the hadronic decay is through the weak interaction. A hadron, in particle physics, is a subatomic particle which experiences the nuclear force. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ...


Since tau-like lepton number is conserved in weak decays, a tau neutrino is created when a tau lepton decays to a muon or electron.


The branching ratio of the common tau decays are: This is a technical term in particle physics and nuclear physics. ...

  • 17.84% for decay into a tau neutrino, electron and electron neutrino
  • 17.36% for decay into a tau neutrino, muon and muon neutrino

The Feynman diagram to the right is incorrect. The tau lepton should decay into a W and a tau neutrino as opposed to a tau antineutrino. This is enforced by conservation of lepton number at the vertex.


Discovery

The tau lepton was detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl with his colleagues at the SLAC-LBL group [1]. Their equipment consisted of SLAC's then-new e+-e colliding ring, called SPEAR, and the LBL magnetic detector. They could detect and distinguish between leptons, hadrons and photons. They did not detect the tau lepton directly, but rather discovered anomalous events: Martin Lewis Perl (b. ... The Stanford Linear Accelerator Center (SLAC) is a U.S. national laboratory operated by Stanford University for the U.S. Department of Energy. ... The Berkeley Lab is perched on a hill overlooking the Berkeley central campus and San Francisco Bay. ... The Stanford Linear Accelerator Center (SLAC) is a U.S. national laboratory operated by Stanford University for the U.S. Department of Energy. ... The Berkeley Lab is perched on a hill overlooking the Berkeley central campus and San Francisco Bay. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...


"We have discovered 64 events of the form



for which we have no conventional explanation."



The need for at least 2 undetected particles was shown by the inability to conserve energy and momentum with only one. However, no other muons, electrons, photons, or hadrons were detected. It was proposed that this event was the production and subsequent decay of a new particle pair:

This was difficult to verify, because the energy to produce the τ+τ pair is similar to the threshold for D meson production. Work done at DESY-Heidelberg, and with the Direct Electron Counter (DELCO) at SPEAR, subsequently established the mass and spin of the tau. The DESY (Deutsches Elektronen Synchrotron, German Electron Synchrotron) is the biggest German research center for particle physics, with sites in Hamburg and Zeuthen. ...


Martin Perl shared the 1995 Nobel Prize for physics with Frederick Reines. The latter was awarded his share of the prize for detecting the neutrino. Frederick Reines Frederick Reines (March 16, 1918 - August 26, 1998) was an American physicist. ...


See also

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. ...

External links

  • Nobel Prize in Physics 1995
  • Perl's logbook showing tau lepton discovery
  • A Tale of Three Papers gives the covers of the three original papers announcing the discovery.

References

  • M. L. Perl et al, "Evidence for Anomalous Lepton Production in e+-e- Annihilation" Phys. Rev. Lett., 35, 1489 (1975)
  • Yao, W. M; et al. (2006). "Tau Lepton". Journal of Physics G 33. 
Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... For the novel, see The Elementary Particles. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... For other uses, see Quark (disambiguation). ... The up quark is a first-generation quark with a charge of +(2/3)e. ... The down quark is a first-generation quark with a charge of -(1/3)e. ... The charm quark is a second-generation quark with a charge of +(2/3)e. ... The strange quark is a second-generation quark with a charge of -(1/3)e and a strangeness of −1. ... The top quark is the third-generation up-type quark with a charge of +(2/3)e. ... The bottom quark is a third-generation quark with a charge of -(1/3)e. ... In physics, a lepton is a particle with spin-1/2 (a fermion) that does not experience the strong interaction (that is, the strong nuclear force). ... 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. ... The muon (from the letter mu (μ)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. ... For other uses, see Neutrino (disambiguation). ... In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... In particle physics, gluons are subatomic particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... In physics, Faddeev-Popov ghost ci is a field that violates the spin-statistics relation. ... In physics, a bound state is a composite of two or more building blocks (particles or bodies) that behaves as a single object. ... A hadron, in particle physics, is a subatomic particle which experiences the nuclear force. ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... Baryon decuplet: Spin=3/2 Baryon octet: Spin=1/2 This is a list of baryons. ... In particle physics, a hyperon is any subatomic particle which is a baryon (and hence a hadron and a fermion) with non-zero strangeness, but with zero charm and zero bottomness. ... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... For other uses, see Proton (disambiguation). ... This article or section does not adequately cite its references or sources. ... The Delta baryon is a relatively light 1,232 MeV/c² baryon which contains only up (u) and down (d) quarks in a combination whose total spin is 3/2 and its ground state parity is +. All varieties of Δ quickly decay via the strong force into an ordinary nucleon plus... In particle physics, the Lambda particle is any one of a number of baryons containing an up quark, a down quark, and a third quark such as that the resulting particle exhibits a state of bottomness, strangeness, or is charmed. ... Properties Sigma particles are baryons composed of one strange quark and a combination of up and down quarks, arranged in an isospin 1 state. ... In particle physics, Ξ (Xi) is a name given to a range of baryons with one up or down quark and two heavier quarks. ... Properties In particle physics, the omega minus (Ω−) is a type of baryon (more specifically, a hyperon). ... The cascade B baryon particle, also known as Ξ-b, was recently discovered by D0 and CDF experiments at Fermilab. ... Mesons of spin 1 form a nonet In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ... A list of mesons. ... In high energy physics, a quarkonium (pl. ... In particle physics, pion (short for pi meson) is the collective name for three subatomic particles: π0, π+ and π−. Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force. ... In particle physics, Kaons (also called K-mesons and denoted K) are a group of four mesons distinguished by the fact that they carry a quantum number called strangeness. ... In particle physics, a rho meson is a short-lived hadronic particle that is an isospin triplet whose three states are denoted as . After the pions and kaons, the rho mesons are the lightest strongly interacting particle with a mass of roughly 770 MeV for all three states. ... The J/ψ is a subatomic particle, namely a flavor-neutral meson consisting of a charm quark and a charm anti-quark. ... The upsilon particle () is a flavorless meson formed from a bottom quark and its antiparticle. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... For other uses, see Atom (disambiguation). ... An exotic atom is the anologue of a normal atom in which one or more of the electrons are replaced by other negative particles, such as a muon or a pion, or the positively charged nucleus is replaced by other positively charged elementary particles, or both. ... Positronium (Ps) is a system consisting of an electron and its anti-particle, a positron, bound together into an exotic atom. The orbit of the two particles and the set of energy levels is similar to that of the hydrogen atom (electron and proton). ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... 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. ... In supersymmetry, it is proposed that every fermion should have a partner boson, known as its Superpartner. ... The axino is a hypothetical elementary particle predicted by some theories of particle physics. ... Dilatino is the superpartner of the dilaton. ... In particle physics, chargino refers to a charged superpartner, i. ... A gluino is a subatomic particle, the fermion superpartner of the gluon predicted by supersymmetry. ... The gravitino is the hypothetical supersymmetric partner of the graviton, as predicted by theories combining general relativity and supersymmetry, i. ... In particle physics, a higgsino is the hypothetical superpartner of the Higgs boson, as predicted by supersymmetry. ... In particle physics, the neutralino is a hypothetical particle and part of the doubling of the menagerie of particles predicted by supersymmetric theories. ... In particle physics, a sfermion is any of the class of spin-0 superpartners of ordinary fermions appearing in supersymmetric extensions to the Standard Model. ... The axion is an exotic subatomic particle postulated by Peccei-Quinn theory to resolve the strong-CP problem in quantum chromodynamics (QCD). ... In theoretical physics, dilaton originally referred to a theoretical scalar field; as a photon refers in one sense to the electromagnetic field. ... In particle and condensed matter physics, Goldstone bosons (also known as Nambu-Goldstone bosons) are bosons that appear in models with spontaneously broken symmetry. ... This article is about the hypothetical particle. ... The Higgs boson, also known as the God particle, is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. ... A tachyon (from the Greek (takhús), meaning swift, fast) is any hypothetical particle that travels at superluminal velocity. ... In particle physics, the X and Y bosons are hypothetical elementary particles analogous to the W and Z bosons, but corresponding to a new type of force, such as the forces predicted by grand unified theory. ... It has been suggested that this article or section be merged with Z boson. ... In particle physics, a Z boson (or Z-prime boson) refers to a hypothetical new neutral gauge boson (named in analogy with the Standard Model Z boson). ... A sterile particle does not have any charge known to us. ... A regular meson made from a quark (q) and antiquark (q-bar) with spins s2 and s1 respectively and having an overall angular momentum L Exotic hadrons are subatomic particles made of quarks (and possibly gluons), but which do not fit into the usual schema of hadrons. ... Ordinary baryons are bound states of 3 quarks. ... A pentaquark is a subatomic particle consisting of a group of five quarks (compared to three quarks in normal baryons and two in mesons), or more specifically four quarks and one anti-quark. ... Identities and classification of possible tetraquark mesons. ... In particle physics, a glueball is a particle containing no valence quarks. ... A tetraquark is a subatomic particle composed of four quarks. ... A mesonic molecule is a set of two or more mesons bound together by the strong force. ... In physics, a quasiparticle refers to a particle-like entity arising in certain systems of interacting particles. ... Side view of an α-helix of alanine residues in atomic detail. ... This page is about the quasiparticle. ... There is a place named Magnon (pronunciation: ma-nyon) in Gabon, see Magnon, Gabon A magnon is a collective excitation of the electrons spin structure in a crystal lattice. ... Normal modes of vibration progression through a crystal. ... In physics, the plasmon is the quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and sound waves, respectively. ... This article is in need of attention. ... In solid-state physics, a polaron is formed when a moving charge (typically an electron or a hole) in a crystal with some ionic character polarizes (by its electric field) the lattice around it. ...

  Results from FactBites:
 
Lepton - Wikipedia, the free encyclopedia (437 words)
The leptons form a family of elementary particles that are distinct from the other known family of fermions, the quarks.
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).
Tau lepton - Wikipedia, the free encyclopedia (486 words)
The tau lepton belongs to the 3rd generation of leptons.
Since tau-like lepton number is conserved (only approximately, due to neutrino oscillations), a tau neutrino is created when a tau lepton decays to a muon or electron.
The tau lepton was detected through a series of experiments between 1974 and 1977 by Martin Lewis Perl with his colleagues at the SLAC-LBL group.
  More results at FactBites »

 
 

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