Electroweak Particles
The electroweak theory of particle physics is a unification of the electromagnetic and weak interactions. Because it is a gauge field theory, the force is transmitted between matter particles by other particles known as gauge bosons. The electroweak particles are the photon, the W boson, and the Z boson. In addition, there is theHiggs boson. All matter particles (quarks and leptons) interact through the electroweak interactions.
The photon is the familiar force-carrier of electromagnetism. It is massless, electrically neutral, and interacts with all particles that carry electric charge. The only matter particles with which the photon does not interact are the three neutrinos, which are electrically neutral. Albert Einstein is usually credited with the discovery of the photon because he used its existence to explain the photoelectric effect in 1905, although Isaac Newton was the first to guess that light had a particle-like character.
The Z boson is one of the force carriers of the weak force. The Z boson is massive, with a mass of 91 GeV/c2 . It is similar to the photon in its interactions because it is electrically neutral, with the exception that it also interacts with neutrinos. The Z boson was discovered at the Large Electron Positron Collider (LEP) at the European Center for Nuclear Research (CERN) in Geneva, Switzerland, in 1983.
The W bosons are also carriers of the weak force. The two W bosons, W+ and W- , are antiparticles of each other. Each W particle has a mass of approximately 80 GeV/c2 . The W+ has electric charge +e and the W- has charge -e. W bosons interact with all particles, and are frequently produced as intermediate particles in the decay of other charged particles. The W boson was discovered along with the Z boson at LEP in 1983. In subsequent experimental runs at LEP, pairs of W bosons were also produced.
The Higgs bosons do not carry the electroweak force, as do the gauge bosons, but have the equally important purpose of generating masses for all of the particles. Higgs bosons are quanta of the Higgs field, a mathematical function that has a value at each point in space-time. Unlike other fields, which have the value zero when there are no particles present, the Higgs field has a constant nonzero component, called its vacuum expectation value, or VEV. Interactions of other particles with the constant Higgs component results in mass terms in the mathematical expression for the particle's energy. Without this Higgs interaction, the other particles would be required to have no mass by the gauge symmetry principle. However, the Higgs boson has not yet been discovered, and its discovery is the highest priority for experimental particle physicists. There are high hopes that the Higgs boson will be discovered soon at either LEP, the newly refurbished Tevatron at Fermilab in Chicago, or the new Large Hadron Collider at CERN.
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