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Weak isospin
 
 
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The weak isospin in particle physics
Particle physics

Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
 is a quantum number relating to the weak interaction
Weak interaction

The weak interaction is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons....
, and parallels the idea of isospin
Isospin

In physics, and specifically, particle physics, isospin is a quantum number related to the strong interaction. This term was derived from isotopic spin, but the term is confusing as two isotopes of a nucleus have different numbers of nucleons; in contrast, rotations of isospin maintain the number of nucleons....
 under the strong interaction
Strong interaction

In particle physics, the strong interaction, or strong force, or color force, holds quarks and gluons together to form protons, neutrons and other particles....
. Weak isospin is usually given the symbol T or I with the third component written as Tz, T3, Iz or I3. Weak isospin is a component of the weak hypercharge
Weak hypercharge

The weak hypercharge in particle physics is a conserved quantum number relating the electrical charge and the third component of weak isospin, and is similar to the Gell-Mann?Nishijima formula for the hypercharge of strong interactions ....
, which unifies weak interactions with electromagnetic
Electromagnetic

Electromagnetic may refer to:* Electromagnetic radiation* Electromagnetism...
 interactions.

Fermion
Fermion

In particle physics, fermions are subatomic particle which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In contrast to bosons, which have Bose-Einstein statistics, only one fermion can occupy a quantum state at a given time; this is the Pauli Exclusion Principle....
s with negative chirality
Chirality (physics)

A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle....
 (also called left-handed fermions) have T = and can be grouped into doublets with Tz = ± that behave the same under the weak interaction
Weak interaction

The weak interaction is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons....
.






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The weak isospin in particle physics
Particle physics

Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
 is a quantum number relating to the weak interaction
Weak interaction

The weak interaction is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons....
, and parallels the idea of isospin
Isospin

In physics, and specifically, particle physics, isospin is a quantum number related to the strong interaction. This term was derived from isotopic spin, but the term is confusing as two isotopes of a nucleus have different numbers of nucleons; in contrast, rotations of isospin maintain the number of nucleons....
 under the strong interaction
Strong interaction

In particle physics, the strong interaction, or strong force, or color force, holds quarks and gluons together to form protons, neutrons and other particles....
. Weak isospin is usually given the symbol T or I with the third component written as Tz, T3, Iz or I3. Weak isospin is a component of the weak hypercharge
Weak hypercharge

The weak hypercharge in particle physics is a conserved quantum number relating the electrical charge and the third component of weak isospin, and is similar to the Gell-Mann?Nishijima formula for the hypercharge of strong interactions ....
, which unifies weak interactions with electromagnetic
Electromagnetic

Electromagnetic may refer to:* Electromagnetic radiation* Electromagnetism...
 interactions.

Fermion
Fermion

In particle physics, fermions are subatomic particle which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In contrast to bosons, which have Bose-Einstein statistics, only one fermion can occupy a quantum state at a given time; this is the Pauli Exclusion Principle....
s with negative chirality
Chirality (physics)

A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle....
 (also called left-handed fermions) have T = and can be grouped into doublets with Tz = ± that behave the same under the weak interaction
Weak interaction

The weak interaction is one of the four fundamental interactions of nature. In the Standard Model of particle physics, it is due to the exchange of the heavy W and Z bosons....
. For example, "u" type quarks (u, c, t) have Tz = + and always transform in "d" type quarks (d, s, b) that have Tz = − and vice versa. On the other hand, a quark never decays into a quark of the same type. Something similar happens with left-handed lepton
Lepton

Leptons are a family of elementary particles, alongside quarks and gauge bosons . Like quarks, leptons are fermions and are subject to the electromagnetic force, the gravitational force, and weak interaction....
s, which exist as doublets containing a charged lepton with Tz = − and a neutrino
Neutrino

Neutrinos are elementary particles that travel close to the speed of light, lack an electric charge, are able to pass through ordinary matter almost undisturbed and are thus extremely difficult to detect....
 with Tz = .

Fermion
Fermion

In particle physics, fermions are subatomic particle which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In contrast to bosons, which have Bose-Einstein statistics, only one fermion can occupy a quantum state at a given time; this is the Pauli Exclusion Principle....
s with positive chirality
Chirality (physics)

A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle....
 (also called right-handed fermions) have T = 0 and form singlets that do not undergo weak interactions.

There is also a weak isospin conservation law: all weak interactions must preserve the weak isospin.

Weak isospin and the W bosons

The symmetry associated with spin is SU(2). This requires gauge boson
Boson

In particle physics, bosons are subatomic particle which obey Bose-Einstein statistics; they are named after Satyendra Nath Bose and Albert Einstein....
s to transform between weak isospin charges: bosons , and . This implies that bosons have a T = 1, with three different values of Tz.

(Tz = +1) is emitted in transitions , boson (Tz = −1) is emitted in transitions . boson (Tz = 0) would be emitted in reactions where Tz does not change. However, under electroweak unification, the boson mixes with the weak hypercharge
Weak hypercharge

The weak hypercharge in particle physics is a conserved quantum number relating the electrical charge and the third component of weak isospin, and is similar to the Gell-Mann?Nishijima formula for the hypercharge of strong interactions ....
 gauge boson , resulting in the observed boson and the photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
 of Quantum Electrodynamics
Quantum electrodynamics

Quantum electrodynamics is a relativity theory quantum field theory of electrodynamics. QED was developed by a number of physicists, beginning in the late 1920s....
.

Sources and footnotes



See also

  • Field theoretical formulation of standard model
    Standard model (basic details)

    This is a detailed description of the Standard Model of particle physics. It describes how the leptons, quarks, gauge bosons and the Higgs boson fit together....
  • Weak hypercharge
    Weak hypercharge

    The weak hypercharge in particle physics is a conserved quantum number relating the electrical charge and the third component of weak isospin, and is similar to the Gell-Mann?Nishijima formula for the hypercharge of strong interactions ....