# 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 .