Neutral current

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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
ee− → ν
ee− 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 1974, in a neutrino experiment in the Gargamelle bubble chamber at CERN.

See also

References

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

External links

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