Text: [QUANT MECH] A particle, such as the electron, proton, or neutron, which obeys the rule that the wave function of several identical particles changes sign when the coordinates of any part are interchanged; it therefore obeys the Pauli exclusion principle. fermions have half-integer values of spin [see BOSON which have integer value spin] An odd half-integer spin particle. Fermions act on each other by exchanging bosons. Examples include leptons (such as the electron), neutrons, protons and quarks. They are indistinguishable, have antisymmetric wave functions, and obey Fermi-Dirac statistics. Fermions obey Fermi-Dirac statistics. Fermions are particles which have half-integer spin and therefore are constrained by the Pauli exclusion principle. Particles with integer spin are called bosons. Fermions incude electrons, protons, neutrons. The wavefunction which describes a collection of fermions must be antisymmetric with respect to the exchange of identical particles, while the wavefunction for a collection of bosons is symmetric. The fact that electrons are fermions is foundational to the buildup of the periodic table of the elements since there can be only one electron for each state in an atom (only one electron for each possible set of quantum numbers). The fermion nature of electrons also governs the behavior of electrons in a metal where at low temperatures all the low energy states are filled up to a level called the Fermi energy. This filling of states is described by Fermi-Dirac statistics. Mesons Mesons are intermediate mass particles which are made up of a quark-antiquark pair. Three quark combinations are called baryons. Mesons are bosons, while the baryons are fermions.

See Also: BOSON

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