Neutral current

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, and confirmed shortly thereafter in 1973, in a neutrino experiment in the Gargamelle bubble chamber at CERN.

See also

• Charged current
• Electric current
• Flavor changing neutral current
• Quantum chromodynamics

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.