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This is a list of particles in particle physics, including currently known and hypothetical elementary particles, as well as the composite particles that can be built up from them.:For a chronological listing of subatomic particles by discovery date, see Timeline of particle discoveries. Elementary particles An elementary particle is a particle with no measurable internal structure, that is, it is not a composite of other particles. They are the fundamental objects of quantum field theory. Elementary particles can be classified according to their spin, with fermions having half-integer spin and bosons integer spin. Standard Model The Standard Model of particle physics is our current understanding of the physics of elementary particles. All Standard Model particles except the Higgs boson have been observed. Fermions (half-integer spin) Fermions have half-integer spin; for all known elementary fermions this is ½. 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 colour force or not. According to the Standard Model, there are 12 flavors of elementary fermions: six quarks and six leptons. Note that the neutrino masses are known to be non-zero because of neutrino oscillation, but their masses are sufficiently light that they have not been measured directly as of 2006. Bosons (integer spin) Bosons have whole number spins. 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 the elementary bosons are: The Higgs boson (spin-0) is predicted by electroweak theory, and is the only Standard Model particle not yet observed. In the Higgs mechanism of the Standard Model, the massive Higgs boson is created by spontaneous symmetry breaking of the Higgs field. The intrinsic masses of the elementary particles (particularly the massive W± and Z0 bosons) would be explained by their interactions with this field. Many physicists expect the Higgs to be discovered at the Large Hadron Collider (LHC) particle accelerator now under construction at CERN. Hypothetical particles Supersymmetric theories predict the existence of more particles, none of which have been confirmed experimentally as of 2006. Other theories predict the existence of additional bosons. Magnetic monopole is a generic name for particles with non-zero magnetic charge. They are predicted by some GUT theories. Tachyon is a generic name for hypothetical particles that travel faster than the speed of light and have an imaginary rest mass. The preon was a suggested substructure for both quarks and leptons, but modern collider experiments have all but disproven their existence. 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) For a detailed list, see List of baryons. Ordinary baryons (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. Mesons (bosons) For a detailed list, see List of mesons. Ordinary mesons (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 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 Isotope table (complete) for a 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, of which 111 have been officially named. Refer to the periodic table for an overview. 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 composites of one 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: Other Classification by speed See also | |||||||
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