This is a list of known and hypothesized molecular, atomic, and subatomic particles inparticle physics,condensed matter physics andcosmology.
Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles.[1] They are the fundamental objects ofquantum field theory. Many families and sub-families of elementary particles exist. Elementary particles are classified according to theirspin.Fermions have half-integer spin whilebosons have integer spin. All the elementary particles of theStandard Model have been experimentally observed, including theHiggs boson in 2012.[2][3] Many other hypothetical elementary particles, such as thegraviton, have been proposed, but not observed experimentally.
| Elementary particles | |||||||||||||||||||||||||||||
| ElementaryfermionsHalf-integerspinObey theFermi–Dirac statistics | ElementarybosonsInteger spinObey theBose–Einstein statistics | ||||||||||||||||||||||||||||
| Quarks and antiquarksSpin =1/2Fractionalelectric chargeHavecolor chargeParticipate in bothstrong interactionsand inelectroweak interactions | Leptons and antileptonsSpin =1/2Integerelectric chargeNo color chargeParticipate inElectroweak interactions | Gauge bosonsSpin = 1Force carriers | Scalar bosonsSpin = 0 | ||||||||||||||||||||||||||
Three generations
| Three kinds
| One kind Higgs boson (H0 ) | |||||||||||||||||||||||||||
Notes:
[†] An anti-electron (e+
) is conventionally called a "positron".
Fermions are one of the two fundamental classes of particles, the other beingbosons. Fermion particles are described byFermi–Dirac statistics and havequantum numbers described by thePauli exclusion principle. They include thequarks andleptons, as well as anycomposite particles consisting of an odd number of these, such as allbaryons and many atoms and nuclei.
Fermions have half-integer spin; for all known elementary fermions this is1/2ħ. All known fermions exceptneutrinos, are alsoDirac fermions; that is, each known fermion has its own distinctantiparticle. It is not known whether theneutrino is aDirac fermion or aMajorana fermion.[4] Fermions are the basic building blocks of allmatter. They are classified according to whether they interact via thestrong interaction or not. In the Standard Model, there are 12 types of elementary fermions: sixquarks and sixleptons.
Quarks are the fundamental constituents ofhadrons and interact via thestrong force. Quarks are the only known carriers offractional charge, but because they combine in groups of three quarks (baryons) or in pairs of one quark and oneantiquark (mesons), only integer charge is observed in nature. Their respectiveantiparticles are theantiquarks, which are identical except that they carry the opposite electric charge (for example the up quark carries charge +2/3e, while the up antiquark carries charge −2/3e), color charge, and baryon number. There are sixflavors 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 [ħ] | Charge [e] | Mass[5][6][7][8] [MeV/c2] |
|---|---|---|---|---|---|---|
| 1 | up | u | u | 1/2 | +2/3 | 2.16±0.07 |
| down | d | d | 1/2 | −1/3 | 4.70±0.07 | |
| 2 | charm | c | c | 1/2 | +2/3 | 1273.0±4.6 |
| strange | s | s | 1/2 | −1/3 | 93.5±0.8 | |
| 3 | top | t | t | 1/2 | +2/3 | 172570±290 |
| bottom | b | b | 1/2 | −1/3 | 4183±7 |
Leptons do not interact via thestrong interaction. Their respectiveantiparticles are theantileptons, which are identical, except that they carry the opposite electric charge and lepton number. The antiparticle of anelectron 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 tooscillate, so that neutrinos of definiteflavor do not have definite mass: instead, they exist in a superposition of masseigenstates. The hypothetical heavy right-handed neutrino, called a "sterile neutrino", has been omitted.
| Generation | Name | Symbol | Antiparticle | Spin [ħ] | Charge [e] | Mass[9] [MeV/c2] |
|---|---|---|---|---|---|---|
| 1 | electron | e− | e+ | 1 /2 | −1 | 0.511[note 1] |
| electron neutrino | ν e | ν e | 1 /2 | 0 | < 0.0000022 | |
| 2 | muon | μ− | μ+ | 1 /2 | −1 | 105.7[note 2] |
| muon neutrino | ν μ | ν μ | 1 /2 | 0 | < 0.170 | |
| 3 | tau | τ− | τ+ | 1 /2 | −1 | 1776.86±0.12 |
| tau neutrino | ν τ | ν τ | 1 /2 | 0 | < 15.5 |
Bosons are one of the two fundamental particles having integral spinclasses of particles, the other beingfermions. Bosons are characterized byBose–Einstein statistics and all have integer spins. Bosons may be either elementary, likephotons andgluons, or composite, likemesons.
According to theStandard Model, the elementary bosons are:
| Name | Symbol | Antiparticle | Spin [ħ] | Charge [e] | Mass[9] [GeV/c2] | Interaction mediated | Observed |
|---|---|---|---|---|---|---|---|
| photon | γ | self | 1 | 0 | 0 | electromagnetism | yes |
| W boson | W− | W+ | 1 | ±1 | 80.385±0.015 | weak interaction | yes |
| Z boson | Z | self | 1 | 0 | 91.1875±0.0021 | weak interaction | yes |
| gluon | g | self | 1 | 0 | 0 | strong interaction | yes |
| Higgs boson | H0 | self | 0 | 0 | 125.09±0.24 | mass | yes |
TheHiggs boson is postulated by theelectroweak theory primarily to explain the origin ofparticle masses. In a process known as the "Higgs mechanism", the Higgs boson and the other gauge bosons in the Standard Model acquire mass viaspontaneous symmetry breaking of the SU(2) gauge symmetry. TheMinimal Supersymmetric Standard Model (MSSM) predicts several Higgs bosons. On 4 July 2012, the discovery of a new particle with a mass between125 and 127 GeV/c2 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 fourfundamental forces of nature are calledforce particles (gauge bosons). Thestrong interaction is mediated by thegluon, theweak interaction is mediated by the W and Z bosons,electromagnetism by the photon, andgravity by the graviton, which is still hypothetical.
Composite particles arebound states of elementary particles.
Hadrons are defined asstrongly interactingcomposite particles. Hadrons are either:
Quark models, first proposed in 1964 independently byMurray Gell-Mann andGeorge Zweig (who called quarks "aces"), describe the known hadrons as composed of valencequarks and/or antiquarks, tightly bound by thecolor force, which is mediated bygluons. (The interaction between quarks and gluons is described by the theory ofquantum chromodynamics.) A "sea" of virtual quark–antiquark pairs is also present in each hadron.
Ordinarybaryons (compositefermions) contain three valence quarks or three valence antiquarks each.
Ordinarymesons are made up of avalence quark and a valenceantiquark. Because mesons have integerspin (0 or 1) and are not themselves elementary particles, they are classified as "composite"bosons, although being made ofelementaryfermions. Examples of mesons include thepion,kaon, and theJ/ψ. Inquantum hadrodynamics, mesons mediate theresidual strong force between nucleons.
At one time or another, positivesignatures have been reported for all of the followingexotic mesons but their existences have yet to be confirmed.
Atomic nuclei typically consist of protons and neutrons, although exotic nuclei may consist of other baryons, such ashypertriton which contains ahyperon. These baryons (protons, neutrons, hyperons, etc.) 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.
Atoms are the smallest neutral particles into which matter can be divided bychemical 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 specificchemical 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 includepionium (π−
π+
) andquarkonium atoms.
Leptonic atoms, named using -onium, are exotic atoms constituted by the bound state of a lepton and an antilepton. Examples of such atoms includepositronium (e−
e+
),muonium (e−
μ+
), and "true muonium" (μ−
μ+
). Of these positronium and muonium have been experimentally observed, while "true muonium" remains only theoretical.
Molecules are the smallest particles into which a substance can be divided while maintaining the chemical properties of the substance. Each type of molecule corresponds to a specificchemical substance. A molecule is a composite of two or more atoms. Atoms are combined in a fixed proportion to form a molecule. Molecule is one of the most basic units of matter.
Ions are charged atoms (monatomic ions) or molecules (polyatomic ions). They include cations which have a net positive charge, and anions which have a net negative charge.
Quasiparticles are effective particles that exist in many particle systems. The field equations ofcondensed matter physics are remarkably similar to those of high energy particle physics. As a result, much of the theory of particle physics applies to condensed matter physics as well; in particular, there are a selection of field excitations, calledquasi-particles, that can be created and explored. These include:
| Name | Symbol | Antiparticle | Spin [ħ] | Charge [e] | Mass[9] [GeV/c2] | Interaction mediated | Observed |
|---|---|---|---|---|---|---|---|
| graviton | G | self | 2 | 0 | 0 | gravitation | no |
Thegraviton is a hypothetical particle that has been included in some extensions to the Standard Model to mediate thegravitational force. It is in a peculiar category between known and hypothetical particles: as an unobserved particle that is not predicted by, nor required for theStandard Model, it belongs in the table of hypothetical particles. But gravitational force itself is a certainty, and expressing that known force in the framework of aquantum field theory requires a boson to mediate it.
If it exists, the graviton is expected to bemassless because the gravitational force has a very long range, and appears to propagate at the speed of light. The graviton must be aspin-2boson because the source of gravitation is thestress–energy tensor, a second-ordertensor (compared withelectromagnetism's spin-1photon, the source of which is thefour-current, a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.[12]
Many hypothetical particle candidates fordark matter have been proposed likeweakly interacting massive particles (WIMP),weakly interacting slender particles (WISP), orfeebly interacting particles (FIP).
Hypothetical particle candidates to explaindark energy include thechameleon particle and theacceleron.
Virtual particles are mathematical tools used in calculations that exhibits some of the characteristics of an ordinary particle but do not obey themass-shell relation. These particles are unphysical and unobservable. These include:
There are alsoinstantons, field configurations which are a local minimum of the Yang–Mills field equation. Instantons are used in nonperturbative calculations of tunneling rates. Instantons have properties similar to particles, specific examples include:
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