This is a list of the different types of particles, known and hypothesized. For a chronological listing of subatomic particles by discovery date, see Timeline of particle discoveries.
This is a list of the different types of particles found in nature. For individual lists of the different particles, see the individual pages given below.
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Elementary particles are particles with no measurable internal structure; that is, they are not 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 particles of the Standard Model have been observed, with the exception of the Higgs boson.
Fermions have half-integer spin; for all known elementary fermions this is 1⁄2. Each fermion has its own distinct antiparticle. Fermions are the basic building blocks of all matter. They are classified according to whether they interact via the color force or not. In the Standard Model, there are 12 types of elementary fermions: six quarks and six leptons.
Quarks are the fundamental constituents of hadrons and interact via the strong interaction. Quarks are the only known carriers of fractional charge, but because they combine in groups of three (baryons) or with their antiparticle (mesons), only integer charge is observed in nature. Their respective antiparticles are the antiquarks which are identical in nearly all respect except that they carry the opposite charge (for example the up quark carries charge +2⁄3, while the up antiquark carries charge −2⁄3). There are six flavours of quarks; the three positively charged quarks are called up-type quarks and the three negatively charged quarks are called down-type quarks.
Name | Symbol | Antiparticle | Charge e |
Mass (MeV/c2) |
---|---|---|---|---|
up | u | u | +2⁄3 | 1.5–3.3 |
down | d | d | −1⁄3 | 3.5–6.0 |
charm | c | c | +2⁄3 | 1,160–1,340 |
strange | s | s | −1⁄3 | 70–130 |
top | t | t | +2⁄3 | 169,100–173,300 |
bottom | b | b | −1⁄3 | 4,130–4,370 |
Leptons do not interact via the strong interaction. Their respective antiparticles are the antileptons which are identical in nearly all respects except that they carry the opposite charge. While the antiparticle of the electron is the antielectron, it is often called 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.
Name | Symbol | Antiparticle | Charge e |
Mass (MeV/c2) |
---|---|---|---|---|
Electron | e− | e+ | −1 | ~ 0.511 |
Electron neutrino | νe | νe | 0 | < 2.2 eV/c2 |
Muon | μ− | μ+ | −1 | ~ 105.6 |
Muon neutrino | νμ | νμ | 0 | < 0.170 |
Tauon | τ− | τ+ | −1 | ~ 1,776.8 |
Tauon neutrino | ντ | ντ | 0 | < 15.5 |
Bosons have integer spin. The fundamental forces of nature are mediated by gauge bosons, and mass is hypothesized to be created by the Higgs boson. According to the Standard Model (and to both linearized general relativity and string theory, in the case of the graviton) the elementary bosons are:
Name | Symbol | Antiparticle | Charge (e) | Spin | Mass (GeV/c2) | Force mediated | Existence |
---|---|---|---|---|---|---|---|
Photon | γ | Self | 0 | 1 | 0 | Electromagnetism | Confirmed |
W boson | W− | W+ | −1 | 1 | 80.4 | Weak | Confirmed |
Z boson | Z | Self? | 0 | 1 | 91.2 | Weak | Confirmed |
Gluon | g | Self? | 0 | 1 | 0 | Strong | Confirmed |
Graviton | G | Self | 0 | 2 | 0 | Gravity | Unconfirmed |
Higgs boson | H0 | Self? | 0 | 0 | > 112 | See below | Unconfirmed |
The Higgs boson (spin-0) is necessitated by electroweak theory primarily to explain the origin of particle masses. Following a process known as the Higgs mechanism, the Higgs boson, and the other fermions in the Standard Model acquire mass via spontaneous symmetry breaking of the SU(2) gauge symmetry. It should be noted that in some theories, the Higgs mechanism, which explains the origin of mass, does not require the existence of a Higgs boson . It is also the only Standard Model particle not yet observed (the graviton is not a standard model particle). Assuming that the Higgs boson exists, it is expected to be discovered at the Large Hadron Collider.
Supersymmetric theories predict the existence of more particles, none of which have been confirmed experimentally as of 2008:
Superpartner | Superpartner of | Spin | Notes |
---|---|---|---|
photino | photon | 1⁄2 | |
gluino | gluon | 1⁄2 | |
Higgsino | Higgs boson | 1⁄2 | |
wino,zino | W and Z bosons | ? | |
gravitino | graviton | 3⁄2 | |
neutralino | neutral bosons | 1⁄2 | The neutralino is a superposition of the superpartners of neutral Standard Model bosons: neutral higgs boson, Z boson and photon. The lightest neutralino is a leading candidate for dark matter. |
chargino | charged bosons | 1⁄2 | The chargino is a superposition of the superpartners of charged Standard Model bosons: charged higgs boson and W boson. |
sterile neutrino | neutrino | ? | Introduced by many extensions of the Standard Model, and may be needed to explain the LSND results. |
sleptons | leptons | 0 | |
squarks | quarks | 0 | The stop squark (superpartner of the top quark) is thought to have a low mass and is often the subject of experimental searches. |
Other theories predict the existence of additional bosons:
Name | Spin | Notes |
---|---|---|
Higgs | 0 | Has been proposed to explain the origin of mass by the spontaneous symmetry breaking of the SU(2) gauge symmetry. |
graviton | 2 | Has been proposed to mediate gravity in theories of quantum gravity. |
graviscalar | 0 | |
graviphoton | 1 | |
axion | 0 | A pseudoscalar particle introduced in Peccei-Quinn theory to solve the strong-CP problem. |
axino | 1⁄2 | Forms, together with the saxion and axion, a supermultiplet in supersymmetric extensions of Peccei-Quinn theory. |
saxion | 0 | |
branon | ? | Predicted in brane world models. |
X and Y bosons | 1 | Predicted by GUT theories to be heavier equivalents of the W and Z. |
W' boson | 1 | |
Z' boson | 1 | |
magnetic photon | ? | |
majoron | 0 | Predicted to understand neutrino masses by the seesaw mechanism. |
Mirror particles are predicted by theories that restore Parity symmetry.
Magnetic monopole is a generic name for particles with non-zero magnetic charge. They are predicted by some GUTs.
Tachyon is a generic name for hypothetical particles that travel faster than the speed of light and have an imaginary rest mass.
Preons were suggested as subparticles of quarks and leptons, but modern collider experiments have all but ruled out their existence.
Kaluza-Klein towers of particles are predicted by some models of extra dimensions. The extra-dimensional momentum is manifested as extra mass in four-dimensional space-time.
Hadrons are defined as strongly interacting composite particles. Hadrons are either:
Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig (who called quarks "aces"), 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.
Notice that mesons are composite bosons, but not composed of bosons. All hadrons, including mesons, are composed of quarks (which are fermions).
Ordinary baryons (composite fermions) contain three valence quarks or three valence antiquarks each.
Some hints at the existence of exotic baryons have been found recently; however, negative results have also been reported. Their existence is uncertain.
Ordinary mesons (composite bosons) contain a valence quark and a valence antiquark, and include the pion, kaon, the J/ψ, and many other types of mesons. In quantum hadrodynamic models, the strong force between nucleons is mediated by mesons.
Exotic mesons may also exist. Positive signatures have been reported for all of these particles at some time, but their existence is still somewhat uncertain.
Atomic nuclei consist of protons and neutrons. Each type of nucleus contains a specific number of protons and a specific number of neutrons, and is called a nuclide or isotope. Nuclear reactions can change one nuclide into another. See table of nuclides for a complete list of isotopes.
Atoms 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. Each type of atom corresponds to a specific chemical element. To date, 117 elements have been discovered (atomic numbers 1-116 and 118), and the first 111 have received official names. Refer to the periodic table for an overview. Atoms consist of protons and neutrons within the nucleus. Within these particles, there are smaller particles still which are then made up of even smaller particles still.
Molecules are the smallest particles into which a non-elemental substance can be divided while maintaining the physical properties of the substance. Each type of molecule corresponds to a specific chemical compound. Molecules are a composite of two or more atoms. See list of compounds for a list of molecules.
The field equations of condensed 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, called quasi-particles, that can be created and explored. These include:
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