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In particle physics, a vector boson is a boson with the spin quantum number equal to 1.
The vector bosons considered to be elementary particles in the Standard Model are the gauge bosons or, the force carriers of fundamental interactions: viz. the photon of electromagnetism, the W and Z bosons of the weak interaction, and the gluon of the strong interaction. There also exist composite particles that are vector bosons, such as the vector mesons, made of a quark and antiquark. For some time, through the 1970s and '80s, intermediate vector bosons, vector bosons of "intermediate" mass, were a major topic in high energy physics.
Vector bosons and the Higgs 
Certain vector bosons, i.e. the Z- and W particles, play a prominent role in the recently announced (July 4, 2012) scalar boson (perhaps the Higgs boson), as shown by the attached Feynman diagram.
Feynman diagram of the fusion of two electroweak vector bosons to the scalar Higgs boson
, which is a prominent process of the generation of Higgs bosons at particle accelerators.
(The symbol q means a quark particle, W and Z are the vector bosons of the electroweak interaction. Ho is the Higgs boson.)
The name vector boson arises from quantum field theory. The component of such a particle's spin along any axis has the three eigenvalues −ħ, 0, and +ħ (where ħ is the reduced Planck constant), meaning that any measurement of it can only yield one of these values. (This is, at least, true for massive vector bosons; the situation is a bit different for massless particles such as the photon, for reasons beyond the scope of this article.) The space of spin states therefore has three degrees of freedom, the same as the number of components of a vector in three-dimensional space. Quantum superpositions of these states can be taken such that they transform under rotations just like the spatial components of a rotating vector. If the vector boson is taken to be the quantum of a field, the field is a vector field, hence the name.
See also