Electroweak Interactions

Abstract

Until 1973 all observed weak interactions were consistent with the hypothesis that they were mediated by the exchange of heavy charged bosons W ^± only. They are called charged current interactions because they change the electric charge of the lepton, for example, in the interaction, $\overline{\nu}_{\mu} + p \rightarrow\mu^{+} + n$, the charge of neutrino is changed when it is destroyed and a new particle (μ ⁺) is produced. Another example is ν _μ +n→μ ⁻+p. Although charged weak processes were recognized from the beginning as in beta decay, the possibility of neutral weak processes was not appreciated until 1958. Typical examples of neutral current events are

$$\begin{aligned} &\overline{\nu}_{\mu} + e^{-} \rightarrow\overline{ \nu}_{\mu} + e^{-},\qquad\nu_{\mu} + e^{-} \rightarrow\nu_{\mu} + e^{-},\qquad\nu_{\mu} + N \rightarrow\nu_{\mu} + \mathrm{hadron}, \\ &\overline{\nu}_{\mu} + p \rightarrow\overline{\nu}_{\mu} + p,\qquad\nu_{\mu} + p \rightarrow\nu_{\mu} + p \end{aligned}$$

They demonstrate the existence of neutral currents because the current connects only muonic lepton with muonic lepton. Both muonic leptons have the same charge (zero) and thus the current must be neutral. Same reasoning applies to electronic lepton and hadron.