Leptons

The leptons – light particles – do not experience the strong interaction. There are twelve leptons:

The electronand the associated electron neutrino

The muonand the associated muon neutrino

The tau particleand associatedneutrino

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

or

Tau Neutrino

0?

0

0

Stable


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 numbersandwhich are +1 for leptons and -1 for the antileptons.