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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 of two types: leptons and quarks. 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 one type of fundamental particle. They have spin 1/2 and are not subject to the strong force. The known leptons are said to be of three families or generations (labeled in the table as 1, 2, 3) and of six flavors, a generic term for the particle names. They are listed in the table below. Their antiparticles also are leptons with opposite electric charge Q and opposite Lepton number L_e,μ,τ.

Lepton flavor properties

Particle name	Symbol	Family/Generation	Q (e)	Le	Lμ	Lτ	Mass (MeV)	Lifetime (s)
Electron	e−	1	−1	+1	0	0	0.510 998 928(11)	Stable
Muon	μ−	2	−1	0	+1	0	105.658 3715(35)	2.197019(21) × 10−6
Tau	τ−	3	−1	0	0	+1	1776.82(16)	2.906(10) × 10-13
Electron neutrino	νe	1	0	+1	0	0	< 0.0000022	Unknown
Muon neutrino	νμ	2	0	0	+1	0	< 0.17	Unknown
Tau neutrino	ντ	3	0	0	0	+1	< 15.5	Unknown

Quarks

Quarks are a type of particle with spin 1/2 that are subject to strong, weak and electromagnetic forces. The known quarks are listed in the table below. The kinds of quark (u, d, c, s, t, d) are referred to as the flavor index of the quark, and besides a flavor index, each quark has a color index, which may be any of three colors: red, green and blue (r, g, b). Their antiparticles also are quarks, but carry anti-colors: anti-red, anti-blue, anti-green.

Quark flavor properties

Name	Symbol	Family/Generation	Mass (MeV)	B	Q(e)	I	C	S	T	B′	Antiparticle	Antiparticle symbol
Up	u	1	2.34 ± 0.19	+1/3	+2/3	+1/2	0	0	0	0	Antiup	ū
Down	d	1	4.78 ± 0.11	+1/3	−1/3	−1/2	0	0	0	0	Antidown	${\overline {d}}$
Charm	c	2	1.294 ± 0.004 × 103	+1/3	+2/3	0	+1	0	0	0	Anticharm	${\overline {c}}$
Strange	s	2	100.2 ± 2.4	+1/3	−1/3	0	0	−1	0	0	Antistrange	${\overline {s}}$
Top	t	3	172.9 ±0.6 ±0.9 × 103	+1/3	+2/3	0	0	0	+1	0	Antitop	${\overline {t}}$
Bottom	b	3	4.19 (+0.18) (−0.06) × 103	+1/3	−1/3	0	0	0	0	−1	Antibottom	${\overline {b}}$

B = baryon number, Q = electric charge, I = isospin, C = charm, S = strangeness, T = topness, B′ = bottomness.
* Notation such as ±xxx denotes measurement uncertainty. In the case of the top quark, the first uncertainty is statistical in nature, and the second is systematic.

The quarks carry fractional electric charge. However, no quark has been observed in isolation, so a "free" fractional electric charge has not been seen.

Quanta

Because gravitation is not included in the standard model, there are three type of interaction included. Each type of interaction is mediated by quanta.

References

NIST