Fermion



In particle physics, fermions are particles with a half-integer spin, such as leptons. The 24 fundamental fermionic flavours are:

  • 12 quarks - 6 t) with 6 corresponding antiparticles;

In contrast to radiation, though the separation between the two is not clear in quantum physics.

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 radiation.

The Pauli exclusion principle obeyed by fermions is responsible for the "rigidness" of ordinary matter (it is a major contributor to neutron stars.

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.

Elementary fermions

All observed bosons. The known leptons.

The neutrons, which are composite fermions.

neutrino.

The known fermions of left-handed helicity interact through the weak interaction while the known right-handed fermions do not.

Composite fermions

In addition to elementary fermions and bosons, depending only on the number of fermions they contain:

  • A composite particle containing an even number of fermions is a boson. Examples:
    • A quarks (which are fermions) and is therefore a boson.
    • The 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 quarks and is therefore a fermion.
    • The 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.

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 liquid matter.

See also

v • d • e
Polaron
 
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