Physics Help
W & Z Boson
W and Z bosons
The W
boson is an elementary
particle, having an
electric charge of just ±1, a mass of
80.4110 GeV (about 80 times the proton's mass), and weak isospin of the
same. There exist three varieties of W bosons: positively-charged types,
negatively-charged (antiparticles of each other) types, and the Z boson,
which possesses no charge whatsoever. 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 (fission).
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 is something of a
conundrum. The W and Z are accurately described by a SU(2)xU(1)
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. Glashow, Weinberg, and 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. At the present time (Sep 25, 2001), the
only missing piece of this model is the Higgs Boson.
Home | Up | Atom | Proton | Neutron | Electron | Quark | Photon | Gluon | W & Z Boson | Graviton | Neutrino
Particle Radiation | Phonon | Roton
Physics Help, made by MultiMedia | Free content and software
This guide is licensed under the GNU
Free Documentation License. It uses material from the Wikipedia.
| 
