List of particles

This is a list of known and hypothesized molecular, atomic, and subatomic particles in particle physics, condensed matter physics and cosmology.

Standard Model elementary particles

Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles. They are the fundamental objects of quantum field theory. Many families and sub-families of elementary particles exist. Elementary particles are classified according to their spin. Fermions have half-integer spin while bosons have integer spin. All the elementary particles of the Standard Model have been experimentally observed, including the Higgs boson in 2012. Many other hypothetical elementary particles, such as the graviton, have been proposed, but not observed experimentally.

Fermions

s are one of the two fundamental classes of particles, the other being bosons. Fermion particles are described by Fermi–Dirac statistics and have quantum numbers described by the Pauli exclusion principle. They include the quarks and leptons, as well as any composite particles consisting of an odd number of these, such as all baryons and many atoms and nuclei.
Fermions have half-integer spin; for all known elementary fermions this is ħ. All known fermions except neutrinos, are also Dirac fermions; that is, each known fermion has its own distinct antiparticle. It is not known whether the neutrino is a Dirac fermion or a Majorana fermion. Fermions are the basic building blocks of all matter. They are classified according to whether they interact via the strong interaction or not. In the Standard Model, there are 12 types of elementary fermions: six quarks and six leptons.

Quarks

s are the fundamental constituents of hadrons and interact via the strong force. Quarks are the only known carriers of fractional charge, but because they combine in groups of three quarks or in pairs of one quark and one antiquark, only integer charge is observed in nature. Their respective antiparticles are the antiquarks, which are identical except that they carry the opposite electric charge, color charge, and baryon number. There are six flavors of quarks; the three positively charged quarks are called "up-type quarks" while the three negatively charged quarks are called "down-type quarks".

Generation	Name	Symbol	Antiparticle	Spin	Charge	Mass
1	up	u			+
1	down	d			−
2	charm	c			+
2	strange	s			−
3	top	t			+
3	bottom	b			−

Leptons

s do not interact via the strong interaction. Their respective antiparticles are the antileptons, which are identical, except that they carry the opposite electric charge and lepton number. The antiparticle of an electron is an antielectron, which is almost always called a "positron" for historical reasons. There are six leptons in total; the three charged leptons are called "electron-like leptons", while the neutral leptons are called "neutrinos". Neutrinos are known to oscillate, so that neutrinos of definite flavor do not have definite mass: instead, they exist in a superposition of mass eigenstates. The hypothetical heavy right-handed neutrino, called a "sterile neutrino", has been omitted.

Generation	Name	Symbol	Antiparticle	Spin	Charge	Mass
1	electron				−1	0.511
1	electron neutrino				0
2	muon				−1	105.7
2	muon neutrino				0
3	tau				−1
3	tau neutrino				0

Bosons

s are one of the two fundamental particles having integral spinclasses of particles, the other being fermions. Bosons are characterized by Bose–Einstein statistics and all have integer spins. Bosons may be either elementary, like photons and gluons, or composite, like mesons.
According to the Standard Model, the elementary bosons are:

Name	Symbol	Antiparticle	Spin	Charge	Mass	Interaction mediated	Observed
photon		self	1	0	0	electromagnetism
W boson			1	±1		weak interaction
Z boson		self	1	0		weak interaction
gluon		self	1	0	0	strong interaction
Higgs boson		self	0	0		mass

The Higgs boson is postulated by the electroweak theory primarily to explain the origin of particle masses. In a process known as the "Higgs mechanism", the Higgs boson and the other gauge bosons in the Standard Model acquire mass via spontaneous symmetry breaking of the SU gauge symmetry. The Minimal Supersymmetric Standard Model predicts several Higgs bosons. On 4 July 2012, the discovery of a new particle with a mass between was announced; physicists suspected that it was the Higgs boson. Since then, the particle has been shown to behave, interact, and decay in many of the ways predicted for Higgs particles by the Standard Model, as well as having even parity and zero spin, two fundamental attributes of a Higgs boson. This also means it is the first elementary scalar particle discovered in nature.
Elementary bosons responsible for the four fundamental forces of nature are called force particles. The strong interaction is mediated by the gluon, the weak interaction is mediated by the W and Z bosons, electromagnetism by the photon, and gravity by the graviton, which is still hypothetical.

Composite particles

Composite particles are bound states of elementary particles.

Hadrons

s are defined as strongly interacting composite particles. Hadrons are either:

Composite fermions, in which case they are called baryons.
Composite bosons, in which case they are called mesons.

Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig, describe the known hadrons as composed of valence quarks and/or antiquarks, tightly bound by the color force, which is mediated by gluons. A "sea" of virtual quark–antiquark pairs is also present in each hadron.

Baryons

Ordinary baryons contain three valence quarks or three valence antiquarks each.

Nucleons are the fermionic constituents of normal atomic nuclei:
* Protons, composed of two up and one down quark
* Neutrons, composed of two down and one up quark
Hyperons, such as the Λ, Σ, Ξ, and Ω particles, which contain one or more strange quarks, are short-lived and heavier than nucleons. Although not normally present in atomic nuclei, they can appear in short-lived hypernuclei.
A number of charmed and bottom baryons have also been observed.
Pentaquarks consist of four valence quarks and one valence antiquark.
Other exotic baryons may also exist.
Mesons

Ordinary mesons are made up of a valence quark and a valence antiquark. Because mesons have integer spin and are not themselves elementary particles, they are classified as "composite" bosons, although being made of elementary fermions. Examples of mesons include the pion, kaon, and the J/ψ. In quantum hadrodynamics, mesons mediate the residual strong force between nucleons.
At one time or another, positive signatures have been reported for all of the following exotic mesons but their existences have yet to be confirmed.

A tetraquark consists of two valence quarks and two valence antiquarks;
A glueball is a bound state of gluons with no valence quarks;
Hybrid mesons consist of one or more valence quark–antiquark pairs and one or more real gluons.
Atomic nuclei

typically consist of protons and neutrons, although exotic nuclei may consist of other baryons, such as hypertriton which contains a hyperon. These baryons which comprise the nucleus are called nucleons. Each type of nucleus is called a "nuclide", and each nuclide is defined by the specific number of each type of nucleon.

"Isotopes" are nuclides which have the same number of protons but differing numbers of neutrons.
Conversely, "isotones" are nuclides which have the same number of neutrons but differing numbers of protons.
"Isobars" are nuclides which have the same total number of nucleons but which differ in the number of each type of nucleon. Nuclear reactions can change one nuclide into another.
Atoms

s are the smallest neutral particles into which matter can be divided by chemical reactions. An atom consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons. An atomic nucleus consists of 1 or more protons and 0 or more neutrons. Protons and neutrons are, in turn, made of quarks. Each type of atom corresponds to a specific chemical element. To date, 118 elements have been discovered or created.
Exotic atoms may be composed of particles in addition to or in place of protons, neutrons, and electrons, such as hyperons or muons. Examples include pionium and quarkonium atoms.