W boson
The W and Z bosons are elementary particles. The two W bosons are antiparticles of each other and have an electric charge of ±1, a mass of 80.4110 GeV (about 80 times the proton's mass), and weak isospin of ±1. The Z boson is its own antiparticle and has a mass of 91.2 Gev and zero electric charge and isospin. The mass of the W and Z bosons is extremely significant as it causes the weak nuclear force to have limited range in contrast to electromagnetism. The W particle is named after the weak nuclear force, and the Z particle was semi-humourously given its name because it was said to be the last particle to need discovery.
The W and Z bosons were first predicted in the 1960s by electroweak theory for which a number of Nobel Prizes were awarded.
The discovery of the W Boson occurred in 1983, during a series of SPS accelerator-based experiments being conducted by Carlo Rubbia and Simon van der Meer, working at the CERN laboratory.
For their efforts, they were awarded the Nobel Prize, one year later.
W and Z bosons mediate the weak nuclear force. The W Boson is best known for mediating reactions for nuclear decay. For example
- n → p + e− +
νe
(neutron decays into proton + electron + anti-neutrino). This reaction is known as beta decay. The opposite process also occurs:
- p + e− → n + νe
(proton + electron goes to neutron + neutrino) and is called electron capture. Since protons are not fundamental particles (they are made up of quarks), it is the quarks that interact. The first example is then
- d → W− + u,
and then the W− decays into an electron and electron-type neutrino.
That the W and Z bosons have mass and photons do not was a major obstacle in developing electroweak theory in the 1960's. The W, Z are accurately described by a SU(2) Gauge theory, but the bosons in a gauge theory must be massless. The photon is also massless because the photon and electromagnetism are described by a U(1) gauge theory. Some mechanism is required to break the SU(2) symmetry, giving mass to the W and Z in the process. The most popular is called the Higgs mechanism, and requires an extra particle, the Higgs Boson.
The combination of the SU(2) gauge theory describing the W and Z, the electromagnetic interaction, and the Higgs mechanism is known as the Glashow-Weinberg-Salam model. Sheldon Glashow, Steven Weinberg, and Abdus Salam won the 1979 Nobel Prize in Physics for this work. These days it is very widely accepted, and has been adopted as part of the standard model of particle physics. As of 2003, the only prediction of the model which has not been experimentally confirmed is the existence of the Higgs Boson.
Referenced By
Carlo Rubbia | Exchange particle | High-energy physics | High energy physics | Kaon | Particle physics | Particle physics foundation ontology | Particles | Particles and fields | PhysIcs | Science/Physics and Hard Sciences | Standard Model | Weak | Weak force | Weak interaction | Weak nuclear force
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