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Encyclopedia > Fermion

In particle physics, fermions are particles with half-integer spin, such as protons and electrons. They are named after Enrico Fermi. In the Standard Model there are two types of elementary fermions: quarks and leptons. Thousands of particles explode from the collision point of two relativistic (100 GeV per ion) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... In mathematics, a half-integer is a number of the form , where is an integer. ... In physics, spin refers to the angular momentum intrinsic to a body, as opposed to orbital angular momentum, which is the motion of its center of mass about an external point. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... e- redirects here. ... Enrico Fermi (September 29, 1901 – November 28, 1954) was an Italian physicist most noted for his work on the development of the first nuclear reactor, and for his contributions to the development of quantum theory, particle physics and statistical mechanics. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... The six flavours of quarks and their most likely decay modes. ... In physics, a particle is a lepton if it has a spin of 1/2 and does not experience the strong nuclear force. ...


In contrast to bosons, only one fermion can occupy a quantum state at a given time. Thus, if more than one fermion occupies the same place in space, the properties of each fermion (e.g. its spin) must be different from the rest. Therefore fermions are usually related with matter while bosons are related with radiation, though the separation between the two is not clear in quantum physics. In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... A quantum state is any possible state in which a quantum mechanical system can be. ... This article or section does not cite any references or sources. ... In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ...

Contents

Basic properties

Due to their half-integer spin, as an observer circles a fermion (or as the fermion rotates 360° about its axis) the wavefunction of the fermion changes sign. A related phenomenon is called an antisymmetric wavefunction behavior of a fermion. Fermions obey Fermi-Dirac statistics, meaning that when one swaps two fermions, the wavefunction of the system changes sign. A consequence of this is the Pauli exclusion principle — no two fermions can occupy the same quantum state at the same time. This results in "rigidness" or "stiffness" of matter which include fermions (atomic nuclei, atoms, molecules, etc), so fermions are sometimes said to be the constituents of matter, and bosons to be particles that transmit interactions (forces), or constituents of radiation. This article discusses the concept of a wavefunction as it relates to quantum mechanics. ... In set theory, the adjective antisymmetric usually refers to an antisymmetric relation. ... Fermi-Dirac distribution as a function of ε/μ plotted for 4 different temperatures. ... This article discusses the concept of a wavefunction as it relates to quantum mechanics. ... The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925. ... A quantum state is any possible state in which a quantum mechanical system can be. ... This article or section does not cite any references or sources. ... Boson (game) Bosons, named after Satyendra Nath Bose, are particles which form totally-symmetric composite quantum states. ... In physics, force is an influence that may cause an object to accelerate. ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ...


The Pauli exclusion principle obeyed by fermions is responsible for the "rigidness" of ordinary matter (it is a major contributor to Young modulus), and for the stability of the electron shells of atoms (thus for stability of atomic matter). It also is responsible for the complexity of atoms (making it impossible for all atomic electrons to occupy the same energy level), thus making complex chemistry possible. It is also responsible for the pressure within degenerate matter which largely governs the equilibrium state of white dwarfs and neutron stars. The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925. ... This article does not adequately cite its references or sources. ... Electron atomic and molecular orbitals In atomic physics and quantum chemistry, the electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure (eg, a crystal). ... It has been suggested that the central science be merged into this article or section. ... Degenerate matter is matter which has sufficiently high density that the dominant contribution to its pressure arises from the Pauli exclusion principle. ... This article or section does not adequately cite its references or sources. ... A neutron star is one of the few possible endpoints of stellar evolution. ...


In large systems, the difference between bosonic and fermionic statistics is only apparent at large densities when their wave functions overlap. At low densities, both types of statistics are well approximated by Maxwell-Boltzmann statistics, which is described by classical mechanics. It has been suggested that the section Physical applications of the Maxwell-Boltzmann distribution from the article Maxwell-Boltzmann distribution be merged into this article or section. ... Classical mechanics is a branch of physics which studies the deterministic motion of objects. ...


Elementary fermions

All observed elementary particles are either fermions or bosons. The known elementary fermions are divided into two groups: quarks and leptons. In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... The six flavours of quarks and their most likely decay modes. ... In physics, a particle is a lepton if it has a spin of 1/2 and does not experience the strong nuclear force. ...


The quarks make up protons and neutrons, which are composite fermions. For other uses of this term, see: Quark (disambiguation) 1974 discovery photograph of a possible charmed baryon, now identified as the Σc++ In particle physics, the quarks are subatomic particles thought to be elemental and indivisible. ... In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... This article or section does not adequately cite its references or sources. ...


Leptons include the electron and similar, heavier particles (muon and tauon) and neutrino. In physics, a particle is a lepton if it has a spin of 1/2 and does not experience the strong nuclear force. ... e- redirects here. ... The muon (from the letter mu (μ)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. ... The tauon, or tau lepton, is a negatively charged elementary particle with a lifetime of 3×10−13 seconds and a high mass of 1777 MeV (compared to 939 MeV for protons and 0. ... Neutrinos are elementary particles denoted by the symbol ν. Travelling close to the speed of light, lacking electric charge and able to pass through ordinary matter almost undisturbed, they are extremely difficult to detect. ...


The known fermions of left-handed helicity interact through the weak interaction while the known right-handed fermions do not. this page is about helicity in fluid mechanics. ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ...


Composite fermions

In addition to elementary fermions and bosons, composite particles (made up of more fundamental particles) are also either fermions or bosons, depending only on the number of fermions they contain: In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ...

  • A composite particle containing an even number of fermions is a boson. Examples:
    • A meson contains two quarks (which are fermions) and is therefore a boson.
    • The nucleus of a carbon-12 atom contains 6 protons and 6 neutrons (all fermions) and is therefore also a boson.
  • A composite particle containing an odd number of fermions is a fermion. Examples:
    • A baryon contains three quarks and is therefore a fermion.
    • The nucleus of a carbon-13 atom contains 6 protons and 7 neutrons and is therefore a fermion.

The number of bosons within a composite particle has no effect on whether it is a boson or a fermion. Mesons of spin 1 form a nonet In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ... The six flavours of quarks and their most likely decay modes. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... Carbon 12 is a stable isotope of the element carbon. ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... The six flavours of quarks and their most likely decay modes. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... Carbon-13 is a stable isotope of carbon. ...


Fermionic or bosonic behavior of a composite particle (or system) is only seen at large (compared to size of the system) distance. At proximity, where spatial structure begins to be important, a composite particle (or system) behaves according to its constituent makeup. For example, two atoms of helium can not share the same space if it is comparable by size to the size of the inner structure of the helium atom itself (~10−10 m)—despite bosonic properties of the helium atoms. Thus, liquid helium has finite density comparable to the density of ordinary liquid matter. General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ...


See also

 v  d  e 
Particles in physics - elementary particles
Fermions: Quarks: (Up · Down · Strange · Charm · Bottom · Top) | Leptons: (Electron · Muon · Tau · Neutrinos)
Gauge bosons: Photon | W and Z bosons | Gluons
Not yet observed: Higgs boson | Graviton | Other hypothetical particles

  Results from FactBites:
 
Fermion - Wikipedia, the free encyclopedia (209 words)
Composite particles composed of fermions may be either fermions or bosons, depending on the number of fermionic constituents: Particles composed of an even number of fermions are themselves bosons (such as mesons); those composed of an odd number of fermions are themselves fermions (such as baryons).
The elementary particles that make up ordinary matter are fermions, belonging to either the quarks (which form protons and neutrons) or the leptons (such as electrons).
The Pauli exclusion principle of fermions is responsible for "rigidness" of ordinary matter and for the stability of the electron shells of atoms, making complex chemistry possible.
  More results at FactBites »

 
 

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