Tauon

τ-lepton
classification
Elementary particle fermion lepton
properties
electric charge	−1  e (−1.602 · 10 −19  C )
Dimensions	1.907 54 (13)  u 3.167 54 (21) · 10 −27  kg 3477.23 (23)  m e
Resting energy	1776.86 (12)  MeV
Compton wavelength	6.977 71 (47) · 10 −16  m
Spin	1/2
average lifespan	290.3 (5) · 10 −15  s
Interactions	weak electromagnetic gravitation

The tauon , also τ-lepton , tau-lepton or τ-particle , is the heaviest of the three charged leptons of the standard model of elementary particles . Its mass is 1777 MeV / c ² and thus about 3500 times the mass of its light sister particle, the electron . Its mean lifespan is about 0.29 picoseconds, making it significantly more unstable than a muon .

Name and discovery

The name Tauon , or the letter τ , was chosen after the Greek word for third (τρίτον, tríton ), because the τ lepton is the third charged electron-like particle. It was discovered in 1975 by Martin L. Perl and his colleagues at SLAC during electron-positron collisions in the SPEAR ring. For this discovery in particular, Perl received the Nobel Prize in Physics in 1995 .

Decay

Feynman diagram of the most common decay channels, which applies ${\displaystyle \pi ^{-}\equiv (d,{\bar {u}})}$

The τ-lepton can decay into the lighter leptons

${\displaystyle {\begin{array}{lcll}\tau ^{-}&\to &e^{-}+{\bar {\nu }}_{e}+\nu _{\tau }\ \quad \quad \quad &(17{,}82\pm 0{,}04)\,\%\\\tau ^{-}&\to &\mu ^{-}+{\bar {\nu }}_{\mu }+\nu _{\tau }&(17{,}39\pm 0{,}04)\,\%\\\end{array}}}$

as well as in different hadrons , e.g. B. pions or kaons . Here is a selection of the numerous decay channels:

${\displaystyle {\begin{array}{lcll}\tau ^{-}&\to &\pi ^{-}+\pi ^{0}+\nu _{\tau }&(25{,}49\pm 0{,}09)\,\%\\\tau ^{-}&\to &\pi ^{-}+\nu _{\tau }&(10{,}82\pm 0{,}05)\,\%\\\tau ^{-}&\to &2\pi ^{-}+\pi ^{+}+\nu _{\tau }&(\ 9{,}31\pm 0{,}05)\,\%\\\tau ^{-}&\to &\pi ^{-}+2\pi ^{0}+\nu _{\tau }&(\ 9{,}26\pm 0{,}10)\,\%\\\tau ^{-}&\to &2\pi ^{-}+\pi ^{+}+\pi ^{0}+\nu _{\tau }&(\ 4{,}62\pm 0{,}05)\,\%\\\tau ^{-}&\to &K^{*}(892)^{-}+\nu _{\tau }&(\ 1{,}20\pm 0{,}07)\,\%\\\tau ^{-}&\to &\pi ^{-}+3\pi ^{0}+\nu _{\tau }&(\ 1{,}04\pm 0{,}07)\,\%\\\tau ^{-}&\to &\pi ^{-}+{\bar {K}}^{0}+\nu _{\tau }&(\ 0{,}840\pm 0{,}014)\,\%\\\tau ^{-}&\to &K^{-}+\nu _{\tau }&(\ 0{,}696\pm 0{,}010)\,\%\\\end{array}}}$

The quark composition of the most commonly involved mesons is:

${\displaystyle {\begin{array}{lcll}|\pi ^{-}\rangle &=&\ |d{\bar {u}}\rangle \\|\pi ^{0}\rangle &=&\left(|u{\bar {u}}\rangle -|d{\bar {d}}\rangle \right)/{\sqrt {2}}\\|K^{-}\rangle &=&\ |s{\bar {u}}\rangle \\|{\bar {K}}^{0}\rangle &=&\ |s{\bar {d}}\rangle \\\end{array}}}$

These mesons are pseudoscalar mesons with total spin 0 and odd parity . It can also vector meson with total spin 1 and odd parity arise, such. B. this : ${\displaystyle J^{P}=0^{-}}$ ${\displaystyle J^{P}=1^{-}}$ ${\displaystyle K^{*}(892)^{-}}$

${\displaystyle {\begin{array}{lcll}|{\bar {K}}^{*}(892)^{-}\rangle &=&|s{\bar {u}}\rangle \end{array}}}$

Individual evidence

1. ↑ The information on the particle properties (info box) is, unless otherwise stated, taken from the publication of the CODATA Task Group on Fundamental Constants : CODATA Recommended Values. National Institute of Standards and Technology, accessed July 4, 2019 . 
2. ↑ ^{a b c} M. Tanabashi et al. ( Particle Data Group ): Review of Particle Physics . In: Physical Review D . tape 98, 030001 , July 31, 2018, doi : 10.1103 / PhysRevD.98.030001 (English, APS download [PDF; 66.9 MB ; accessed on July 4, 2019]).
3. ^ Martin L. Perl: Evidence for, and properties of, the new charged heavy lepton. In: Tran Thanh Van (ed.): Proceedings of the XII Rencontre de Moriond. 1977. (SLAC-PUB-1923, PDF ).
4. ↑ ML Perl et al .: Evidence for Anomalous Lepton Production in e + -e- Annihilation . In: Physical Review Letters . 35, No. 22, 1975, pp. 1489-1492. doi : 10.1103 / PhysRevLett.35.1489 .