From two mesons and weak currents to the standard model

Suffice to say, the maximal parity violation seen in beta decay during those early years was consistent with a combination of S and T interactions together with a right-handed neutrino (vR)or a combination of V and A interactions together with a left-handed neutrino (vL). The observation of maximal parity violation in muon decay, however, mandated a combination of V and A interaction together with VL. It was for this reason that Sudarshan and I, after reanalysing all the experimental data on parity-conserving and parity-violating experiments in beta and muon decay as well as the experiment on the [n —> ev/n ~ l~v] ratio R, argued that the only possible universal weak interaction was V - A with a vL and that the universal V - A theory could only survive if the claims of four experiments at that time were incorrect. Those experiments were: (a) electron-neutrino angular correlation in He6*; (b) sign of the electron polarization from muon decay; (c) frequency of the electron mode in pion decay; (d) asymmetry from polarized neutron decay. Within the next two years, those four experiments were all redone and the new results were in complete accord with the V - A theory. Within the same two-year period, Goldhaber et al (1958) carried out their ingenious experiment to directly measure the neutrino helicity, which they found to be left-handed, thereby giving powerful support to the universal V-A theory. * It was this experiment, almost universally accepted in the Spring of 1957 (Rustad and Ruby 1955), that led T D Lee to state at the Seventh Rochester Conference (Lee 1957) that: "Beta decay information tells us that the interaction between (p,n) and (e,v) is scalar and tensor, while the two-component neutrino theory plus the law of conservation of leptons implies that the coupling between (e,v)and(/z,v) is vector. This means that the universal Fermi interaction cannot be realized in the way we have expressed it.