Elementary particles are particles for which there is no known way of dividing them into smaller units. Theoretical and experimental studies have shown that the spin possessed by such particles cannot be explained by postulating that they are made up of even smaller particles rotating about a common center of mass (see classical electron radius); as far as can be determined, these elementary particles have no inner structure. The spin of an elementary particle is a truly intrinsic physical property, akin to the particle's electric charge and rest mass.
It turns out that a convenient definition of the spin quantum number s is s = n/2, where n can be any non-negative integer. Hence the allowed values of s are 0, 1/2, 1, 3/2, 2, etc. The value of s for an elementary particle depends only on the type of particle, and cannot be altered in any known way.
All known matter is ultimately composed of elementary particles called fermions, and all elementary fermions have s = 1/2. Examples of fermions are the electron and positron, the quarks making up protons and neutrons, and the neutrinos. Elementary particles emit and receive one or more particles called bosons. This boson exchange gives rise to the three fundamental interactions ("forces") of the Standard model of particle physics; hence bosons are also called force carriers. These bosons have s=1. A basic example for a boson is the photon. Electromagnetism is the force that results when charged particles exchange photons.
Theory predicts the existence of two bosons whose s differs from 1. The force carrier for gravity is the hypothetical graviton; theory suggests that it has s = 2. The Higgs mechanism predicts that elementary particles acquire nonzero rest mass by exchanging hypothetical Higgs bosons with an all-pervasive Higgs field. Theory predicts that the Higgs boson has s = 0. If so, it would be the only elementary particle for which this is the case.
http://en.wikipedia.org/wiki/Spin_%28physics%29
It turns out that a convenient definition of the spin quantum number s is s = n/2, where n can be any non-negative integer. Hence the allowed values of s are 0, 1/2, 1, 3/2, 2, etc. The value of s for an elementary particle depends only on the type of particle, and cannot be altered in any known way.
All known matter is ultimately composed of elementary particles called fermions, and all elementary fermions have s = 1/2. Examples of fermions are the electron and positron, the quarks making up protons and neutrons, and the neutrinos. Elementary particles emit and receive one or more particles called bosons. This boson exchange gives rise to the three fundamental interactions ("forces") of the Standard model of particle physics; hence bosons are also called force carriers. These bosons have s=1. A basic example for a boson is the photon. Electromagnetism is the force that results when charged particles exchange photons.
Theory predicts the existence of two bosons whose s differs from 1. The force carrier for gravity is the hypothetical graviton; theory suggests that it has s = 2. The Higgs mechanism predicts that elementary particles acquire nonzero rest mass by exchanging hypothetical Higgs bosons with an all-pervasive Higgs field. Theory predicts that the Higgs boson has s = 0. If so, it would be the only elementary particle for which this is the case.
http://en.wikipedia.org/wiki/Spin_%28physics%29
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