List of particles

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 or believed to exist in the whole of the universe. For individual lists of the different particles, see the individual pages given below.

Contents

Elementary particles

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

Fermions have half-integer spin; for all known elementary fermions this is 12. All known fermions are 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.[1] 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

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 in groups of two with antiquarks (mesons), only integer charge is observed in nature. Their respective antiparticles are the antiquarks which are identical except for the fact that they carry the opposite electric charge (for example the up quark carries charge +23, while the up antiquark carries charge −23), color charge, and baryon number. 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.

Quarks
Name Symbol Antiparticle Charge
e
Mass (MeV/c2)
up u u +23 1.5–3.3
down d d 13 3.5–6.0
charm c c +23 1,160–1,340
strange s s 13 70–130
top t t +23 169,100–173,300
bottom b b 13 4,130–4,370

Leptons

Leptons do not interact via the strong interaction. Their respective antiparticles are the antileptons which are identical except for the fact that they carry the opposite electric charge and lepton number. The antiparticle of the electron is the antielectron, which is nearly always 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.

Leptons
Name Symbol Antiparticle Charge
e
Mass (MeV/c2)
Electron e
e+
−1 0.511
Electron neutrino ν
e
ν
e
 0
Muon μ
μ+
−1 105.7
Muon neutrino ν
μ
ν
μ
0 < 0.170
Tau τ
τ+
−1 1,777
Tau neutrino ν
τ
ν
τ
0 < 15.5

Bosons

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) Interaction mediated Existence
Photon γ Self 0 1 0 Electromagnetism Confirmed
W boson W
W+
−1 1 80.4 Weak interaction Confirmed
Z boson Z Self 0 1 91.2 Weak interaction Confirmed
Gluon g Self 0 1 0 Strong interaction Confirmed
Higgs boson H0
Self 0 0 > 112 None Unconfirmed
Graviton G Self 0 2 0 Gravitation Unconfirmed

The graviton is added to the list although it is not predicted by the Standard Model, but by other theories in the framework of quantum field theory.

The Higgs boson is postulated by electroweak theory primarily to explain the origin of particle masses. In 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 is the only Standard Model particle not yet observed (the graviton is not a Standard Model particle). The Minimal Supersymmetric Standard Model (MSSM) predicts several Higgs bosons. If the Higgs boson exists, it is expected to be discovered at the Large Hadron Collider.

Hypothetical particles

Supersymmetric theories predict the existence of more particles, none of which have been confirmed experimentally as of 2011:

Superpartners
Superpartner Superpartner of Spin Notes
neutralino neutral bosons 12 The neutralinos are superpositions 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.
The MSSM predicts 4 neutralinos
chargino charged bosons 12 The charginos are superpositions of the superpartners of charged Standard Model bosons: charged higgs boson and W boson.
The MSSM predicts two pairs of charginos.
photino photon 12 Mixing with zino, neutral wino, and neutral Higgsinos for neutralinos.
wino, zino W± and Z0 bosons 12 Charged wino mixing with charged Higgsino for charginos, for the zino see line above.
Higgsino Higgs boson 12 For supersymmetry there is a need for several Higgs bosons, neutral and charged, according with their superpartners.
gluino gluon 12 Eight gluons and eight gluinos.
gravitino graviton 32 Predicted by Supergravity (SUGRA). The graviton is hypothetical, too – see next table.
sleptons leptons 0 The superpartners of the leptons (electron, muon, tau) and the neutrinos.
sneutrino neutrino 0 Introduced by many extensions of the Standard Model, and may be needed to explain the LSND results.
A special role has the sterile sneutrino, the supersymmetric counterpart of the hypothetical right-handed neutrino, called sterile neutrino
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.

Note: Just as the photon, Z boson and W± bosons are superpositions of the B0, W0, W1, and W2 fields – the photino, zino, and wino± are superpositions of the bino0, wino0, wino1, and wino2 by definition.
No matter if you use the original gauginos or this superpositions as a basis, the only predicted physical particles are neutralinos and charginos as a superposition of them together with the Higgsinos.

Other theories predict the existence of additional bosons:

Other hypothetical bosons and fermions
Name Spin Notes
Higgs 0 Has been proposed to explain the origin of mass by the spontaneous symmetry breaking of the SU(2) x U(1) gauge symmetry.
SUSY theories predict more than one type of Higgs boson
graviton 2 Has been proposed to mediate gravity in theories of quantum gravity.
graviscalar 0 Also known as radion
graviphoton 1 Also known as gravivector[2]
axion 0 A pseudoscalar particle introduced in Peccei-Quinn theory to solve the strong-CP problem.
axino 12 Superpartner of the axion. Forms, together with the saxion and axion, a supermultiplet in supersymmetric extensions of Peccei-Quinn theory.
saxion 0
branon  ? Predicted in brane world models.
dilaton 0 Predicted in some string theories.
dilatino 12 Superpartner of the dilaton
X and Y bosons 1 These leptoquarks are predicted by GUT theories to be heavier equivalents of the W and Z.
W' and Z' bosons 1
magnetic photon  ?
majoron 0 Predicted to understand neutrino masses by the seesaw mechanism.
majorana fermion 12 ; 32 ?... Gluinos, neutralinos, or other

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.

Composite particles

Hadrons

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.

Baryons (fermions)

A combination of three u, d or s-quarks with a total spin of 32 form the so-called baryon decuplet.
Proton quark structure: 2 up quarks and 1 down quark.
For a detailed list, see List of baryons.

Ordinary baryons (composite fermions) 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 (uud)
    • Neutrons, composed of two down and one up quark (ddu)
  • 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.

Some hints at the existence of exotic baryons have been found recently; however, negative results have also been reported. Their existence is uncertain.

  • Pentaquarks consist of four valence quarks and one valence antiquark.

Mesons (bosons)

Mesons of spin 0 form a nonet
For a detailed list, see List of mesons.

Ordinary mesons are made up of a valence quark and a valence antiquark. Because mesons have spin of 0 or 1 and are not themselves elementary particles, they are composite bosons. Examples of mesons include the pion, kaon, the J/ψ. In quantum hadrodynamic models, 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 existence has 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

A semi-accurate depiction of the helium atom. In the nucleus, the protons are in red and neutrons are in purple. In reality, the nucleus is also spherically symmetrical.

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

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, 118 elements have been discovered, while only the first 112 have received official names. Refer to the periodic table for an overview.

The atomic nucleus consists of protons and neutrons. Protons and neutrons are, in turn, made of quarks.

Molecules

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.

Condensed matter

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:

  • Phonons are vibrational modes in a crystal lattice.
  • Excitons are bound states of an electron and a hole.
  • Plasmons are coherent excitations of a plasma.
  • Polaritons are mixtures of photons with other quasi-particles.
  • Polarons are moving, charged (quasi-) particles that are surrounded by ions in a material.
  • Magnons are coherent excitations of electron spins in a material.

Other

  • An anyon is a generalization of fermion and boson in two-dimensional systems like sheets of graphene which obeys braid statistics.
  • A plekton is a theoretical kind of particle discussed as a generalization of the braid statistics of the anyon to dimension > 2.
  • A WIMP (weakly interacting massive particle) is any one of a number of particles that might explain dark matter (such as the neutralino or the axion).
  • The pomeron, used to explain the elastic scattering of Hadrons and the location of Regge poles in Regge theory.
  • The skyrmion, a topological solution of the pion field, used to model the low-energy properties of the nucleon, such as the axial vector current coupling and the mass.
  • A genon is a particle existing in a closed timelike world line where spacetime is curled as in a Frank Tipler or Ronald Mallett time machine.
  • A goldstone boson is a massless excitation of a field that has been spontaneously broken. The pions are quasi-Goldstone bosons (quasi- because they are not exactly massless) of the broken chiral isospin symmetry of quantum chromodynamics.
  • A goldstino is a Goldstone fermion produced by the spontaneous breaking of supersymmetry.
  • An instanton is a field configuration which is a local minimum of the Euclidean action. Instantons are used in nonperturbative calculations of tunneling rates.
  • A dyon is a hypothetical particle with both electric and magnetic charges
  • A geon is an electromagnetic or gravitational wave which is held together in a confined region by the gravitational attraction of its own field energy.
  • An inflaton is the generic name for an unidentified scalar particle responsible for the cosmic inflation.
  • A spurion is the name given to a "particle" inserted mathematically into an isospin-violating decay in order to analyze it as though it conserved isospin.

Classification by speed

  • A tardyon or bradyon travels slower than light and has a non-zero rest mass.
  • A luxon travels at the speed of light and has no rest mass.
  • A tachyon (mentioned above) is a hypothetical particle that travels faster than the speed of light and has an imaginary rest mass.

See also

References

  1. ^ B. Kayser, Two Questions About Neutrinos, arXiv:1012.4469v1 [hep-ph] (2010).
  2. ^ R. Maartens (2004). Brane-World Gravity. 7. 7. http://www.emis.de/journals/LRG/Articles/lrr-2004-7/download/lrr-2004-7BW.pdf.  Also available in web format at http://www.livingreviews.org/lrr-2004-7.


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