List of particles -1
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 list below.
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 whilebosons have integer spin. All the particles of the Standard Model have been experimentally observed, recently including the Higgs boson.
Fermions
Fermions 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 1⁄2. 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.[3] Fermions are the basic building blocks of allmatter. 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 theantiquarks, which are identical except for the fact that they carry the opposite electric charge (for example the up quark carries charge +2⁄3, while the up antiquark carries charge −2⁄3), color charge, and baryon number. There are six flavors 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
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 anelectron is an antielectron, which is nearly 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, rather they exist in a superposition of mass eigenstates. The hypothetical heavy right-handed neutrino, called a "sterile neutrino", has been left off the list.
| Name | Symbol | Antiparticle | Charge (e) | Mass (MeV/c2) |
|---|---|---|---|---|
| Electron | e− | e+ | −1 | 0.511 |
| Electron neutrino | ν e | ν e | 0 | < 0.000 0022 |
| 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 are one of the two fundamental classes 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.
The fundamental forces of nature are mediated by gauge bosons, and mass is believed to be created by theHiggs field. According to the Standard Model 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 | 125.3 | Mass | Confirmed |
| Graviton | G | Self | 0 | 2 | 0 | Gravitation | Unconfirmed |
The graviton is added to the list[citation needed] although it is not predicted by the Standard Model, but by other theories in the framework of quantum field theory. Furthermore, gravity is non-renormalizable. There are a total of eight independent gluons. 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(2) gauge symmetry. TheMinimal Supersymmetric Standard Model (MSSM) predicts several Higgs bosons. A new particle expected to be the Higgs boson was observed at the CERN/LHC on March 14, 2013, around the energy of 126.5GeV with an accuracy of close to five sigma (99.9999%, which is accepted as definitive). The Higgs mechanism giving mass to other particles has not been observed yet.
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