Neutral current

Electromagnetism

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Weak neutral current interactions are one of the ways in which subatomic particles can interact by means of the weak force. These interactions are mediated by the
Z
boson. The discovery of weak neutral currents was a significant step toward the unification of electromagnetism and the weak force into the electroweak force, and led to the discovery of the W and Z bosons.

Definition

The neutral current that gives the interaction its name is that of the interacting particles. For example, the neutral-current contribution to the
ν
e
e−
→
ν
e
e−
elastic scattering amplitude

{\mathfrak {M}}^{{{\mathrm {NC}}}}\propto J_{{\mu }}^{{{\mathrm {(NC)}}}}(\nu _{{{\mathrm {e}}}})\;J^{{{\mathrm {(NC)}}\mu }}({\mathrm {e^{{-}}}})

where the neutral currents describing the flow of the neutrino and of the electron are given by

J^{{{\mathrm {(NC)}}\mu }}(f)={\bar {u}}_{{f}}\gamma ^{{\mu }}{\frac {1}{2}}\left(g_{{V}}^{{f}}-g_{{A}}^{{f}}\gamma ^{{5}}\right)u_{{f}},

and $g_{{V}}^{{f}}$ and $g_{{A}}^{{f}}$ are the vector and axial vector couplings for fermion $f$ .

The
Z
boson can couple to any Standard Model particle, except gluons and photons. However, any interaction between two charged particles that can occur via the exchange of a virtual
Z
boson can also occur via the exchange of a virtual photon. Unless the interacting particles have energies on the order of the
Z
boson mass (91 GeV) or higher, the virtual
Z
boson exchange has an effect of a tiny correction ( $~(E/M_{Z})^{2}$ ) to the amplitude of the electromagnetic process. Particle accelerators with energies necessary to observe neutral current interactions and to measure the mass of
Z
boson weren't available until 1983.

On the other hand,
Z
boson interactions involving neutrinos have distinctive signatures: They provide the only known mechanism for elastic scattering of neutrinos in matter; neutrinos are almost as likely to scatter elastically (via
Z
boson exchange) as inelastically (via
W
boson exchange). Weak neutral currents were predicted in 1973 by Abdus Salam, Sheldon Glashow and Steven Weinberg,^[1] and confirmed shortly thereafter in 1973, in a neutrino experiment in the Gargamelle bubble chamber at CERN.

References

↑ "The Nobel Prize in Physics 1979". Nobel Foundation. Retrieved 2008-09-10.

External links

THE DISCOVERY OF WEAK NEUTRAL CURRENTS, CERN Courier
public web CERN
britannica
R Nave
http://www.actaphys.uj.edu.pl/vol37/pdf/v37p2295.pdf
http://www.symmetrymagazine.org/breaking/2009/07/07/gargamelle/
cerncourier
Padilla, Antonio (Tony). "Gargamelle and Neutral Currents". Sixty Symbols. Brady Haran for the University of Nottingham.

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Neutral current

Definition

See also

References

External links