The leptons – light particles – do not experience the strong interaction. There are twelve leptons:
The electron
and the associated electron neutrino
The muon
and the associated muon neutrino
The tau particle
and associated
neutrino
Each of these particles has an antiparticle giving twelve leptons in total.
All the leptons have spin
– they are fermions and obey the exclusion principle.
More properties are summarized in the table below.
|
Particle |
Symbol |
Antiparticle |
Mass |
|
|
|
Lifetime (s) |
Principle Decay Modes |
|
Electron |
|
|
0.511 |
|
0 |
0 |
Stable |
|
|
Electron Neutrino |
|
|
0? |
|
0 |
0 |
Stable |
|
|
Muon |
|
|
105.7 |
0 |
|
0 |
|
|
|
Muon Neutrino |
|
|
0? |
0 |
|
0 |
Stable |
|
|
Tau |
|
|
1777 |
0 |
0 |
|
|
|
|
Tau Neutrino |
|
|
0? |
0 |
0 |
|
Stable |
|
or
Despite all having no charges, each neutrino is distinct from it's associated antineutrino. The spin angular momentum of a neutrino has a component that is opposite to it's linear momentum while that of an antineutrino is parallel to it's linear momentum.
Leptons obey a conservation principle. Corresponding to the three pairs of leptons there are three lepton numbers
and
which are +1 for leptons and -1 for the antileptons.