The tauon, or tau lepton, is a negatively charged elementary particle with a lifetime of 3×10⁻¹³ seconds and a high mass of 1777 MeV (compared to 939 MeV for protons and 0.511 MeV for electrons). It has an associated antiparticle (the anti-tauon) and neutrinos (the tau neutrino and tau antineutrino). In particle physics, an elementary particle is a particle of which other, larger particles are composed. ... Mass is a property of physical objects that, roughly speaking, measures the amount of matter they contain. ... The neutrino is an elementary particle. ... An antineutrino is the antimatter equivalent particle of the neutrino. ...

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 tauon has a spin of 1/2. The tau lepton and its antiparticle carry the same electric charges as the electron and positron, respectively. According to the standard model of particle physics, all the elementary particles seen in particle collision experiments can be divided into three generations. ... In physics, a particle is a lepton if it has a spin of 1/2 and does not experience the strong nuclear force. ... Properties The electron is a subatomic particle. ... The moons shadow, as seen in muons 700m below ground at the Soudan 2 detector. ... In physics, spin is an intrinsic angular momentum associated with microscopic particles. ... The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle of the electron. ...

Decay

The tauon 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 tauon, the hadronic decay is through the weak interaction. In particle physics, a hadron is a subatomic particle which experiences the strong 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 (only approximately, due to neutrino oscillations), a tau neutrino is created when a tauon decays to a muon or electron. Neutrino oscillation refers to the phenomenon of neutrinos oscillating between behaving like different flavors, in the sense that the flavor eigenstates are defined as the wavefunction that will produce a charged lepton of a particular type (electron, muon or tau lepton) when interacting with a W-boson, and a neutrino...

The branching ratio for the decay of a tauon into an electron and neutrinos is about 18%, and similar for decay into a muon and neutrinos. The branching ratio for hadronic decay is about 64%. This is a technical term in particle physics and nuclear physics. ...

Discovery

The tauon was detected in 1975 by Martin Lewis Perl with his colleagues at the SLAC-LBL group. Their equipment consisted of SLAC's 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 tauon directly, rather they 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. ... For the Science Fiction weapon, as seen in Star Trek, see Photon torpedo. ...

There must have been undetected particles because not all energy from the initial collision could be accounted for in the final state. However, they did not detect any other muons or electrons, or any hadrons or photons. 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 tauon. The DESY (Deutsches Elektronen Synchrotron, German Electron Synchrotron) is a German physics research institute. ...

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

• List of particles

List of particles in particle physics. ...

References

• M. L. Perl et al, "Evidence for Anomalous Lepton Production in e⁺-e^- Annihilation" Phys. Rev. Lett., 35, 1489 (1975)