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.
]]>Strangeness of the particles is shown vertically and charge diagonally upwards to the left. The Eightfold Way may be understood as a consequence of flavor symmetries between quarks. The strong nuclear force affects quarks inthe same way regardless of their flavor, so replacing one flavor of quark with another in a hadron should not alter its mass very much. The quarks form what is known in Maths as a group.
The theory was supported by the discovery of the discovery of the {jatex options:inline}\Omega^{}{/jatex} particle with a charge of 1, strangeness of 3 and tmaas predicted by the full version of the theory when extended to particles with other spins..



Mediating Particle 

Force 
Relative Strength 
Range 
Name 
Mass 
Charge 
Spin 
Strong 
1 
Short 
Gluon 
0? 
0 
1 
Electromagnetic 
Infinite 
Photon 
0 
0 
1 

Weak 
Short 
80.4, 80.4, 91.2 resp 
1 

Gravity 
Infinite 
Graviton 
0 
0 
2 
There are several things to note:
Both gravity and the electromagnetic force have infinite range. The mediating particle of both these forces are stable and do not decay spontaneously. This means that the flux of the force particles through a sphere drawn around the source of the force is a constant no matter how big the sphere, and this implies the force must obey alaw.
The weak force is mediated by massive particles. We may find the approximate range of the weak force using Heisenberg's Uncertainty Principle for virtual particles
We can estimate the range of the force now by assuming the force particles travel at the speed of light for this time.
This approach is general and can be used to estimate the range of forces from the masses of the mediating particle.
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