User:John R. Brews/Sample2

The Standard Model of particle physics is the mathematical theory that describes the weak, electromagnetic and strong interactions between leptons and quarks, the basic particles of particle physics. This model is very strongly supported by experimental observations, and is considered to be a major achievement (perhaps the most outstanding achievement) of theoretical physics. It does not, however, treat the gravitational force, inclusion of which remains an elusive goal of the ultimate "theory of everything". The Standard Model is accordingly not consistent with general relativity. The theory is consistent with special relativity.

The model is only qualitatively described in this article, and mathematical details are not provided. To begin, the basic particles in the Standard Model and their interactions are introduced.

Particles and interactions

The interactions between the particles of the Standard Model are well known experimentally, and transcend the Standard Model. However, the particles of the Standard Model are introduced with the ways that they use these interactions to assemble a complete theory of the interactions between various manifestations of matter. The fundamental particles are spin 1/2 fermions, and their interactions are viewed as exchange forces, which is to say the forces are introduced by the trading back and forth of force carriers, different kinds of particle that represent quanta of the underlying force fields. So, for example, the quanta of the electromagnetic field are photons. The strength of an electromagnetic field is dictated by the number of photons that make it up, and the exchange of photons between particles with electric charge is the mechanism underlying the field's ability to exert an electromagnetic force upon these bodies.

Leptons

Leptons are spin 1/2 fermions that are not subject to the strong force. The known leptons are listed int he table below.

Properties of leptons

Particle/Antiparticle Name	Symbol	Q (e)	Spin	Le	Lμ	Lτ	Mass (MeV/c2)	Lifetime (s)	Common decay
Electron	e−	−1	1/2	+1	0	0	0.510998910(13)	Stable	Stable
Muon	μ−	−1	1/2	0	+1	0	105.6583668(38)	2.197019(21) × 10−6	$e^{-}+{\overline {\nu }}_{e}+\nu _{\mu }$
Tau	τ−	−1	1/2	0	0	+1	1776.84(17)	2.906(10) × 10-13	$\pi ^{-}+\nu _{\tau };\$ $\mu ^{-}+{\overline {\nu }}_{\mu }+\nu _{\tau };\$ $e^{-}+{\overline {\nu }}_{e}+\nu _{\tau }$
Electron neutrino	νe	0	1/2	+1	0	0	< 0.0000022	Unknown
Muon neutrino	νμ	0	1/2	0	+1	0	< 0.17	Unknown
Tau neutrino	ντ	0	1/2	0	0	+1	< 15.5	Unknown

References

NIST