Leptons

Name

Symbol

Mass

Lifetime

Charge

Spin

Date

Source

Note

Family 1

Electron

e

0.511 Mev

Stable

-1

1/2

1897

Cathode Ray Tube

(Carrier of Electricity)

Common Matter,

Discovered By J.J. Thompson

Positron

e +

0.511 Mev

Stable

+1

1/2

1932

Cosmic Radiation

Common Anti-Matter

Formed by Cosmic Radiation

Electron Neutrino

v e

0 (?)

< 50 ev

Stable (?)

0

1/2

1956

Nuclear Reactor

Common Matter,

Produced by Weak Force

Electron

Anti-Neutrino

v e

0 (?)

< 50 ev

Stable (?)

0

1/2

1956

Nuclear Reactor

Common Anti-Matter,

Produced by Weak Force

Family 2

Muon



105.6

2x10-6

-1

1/2

1937

Cosmic Radiation

Pion, Kaon -> Muon

Uncommon Matter

Anti -Muon



105.6

2x10-6

+1

1/2

1937

Cosmic Radiation

Uncommon Matter,

Compose Cosmic Radiation

Muon

Neutrino

v u

0 (?)

< .5 Mev

Stable (?)

0

1/2

1962

Pion Decay in

Uncommon Matter,

Muon

Anti-Neutrino

v u

0 (?)

< .5 Mev

Stable (?)

0

1/2

1962

Pion Decay in Accelerators

Uncommon Matter

Produced by Weak Force

Family 3

Tau

t +

1.784 Gev

3x10-13

-1

1/2

1975

Electron-Positron Annihilation

Rare Matter

Anti-Tau

t -

1.784 Gev

3x10-13

+1

1/2

1975

Electron-Positron Annihilation

Rare Anti-Matter

Tau

Neutrino

v t

0 (?)

< 70 Mev

Stable (?)

0

1/2

---

Inferred from

Tau Decay

Rare Matter

Tau

Anti-Neutrino

vt

0 (?)

< 70 Mev

Stable (?)

0

1/2

---

No Direct Generation

Rare Anti-Matter