Induced Pseudoscalar Interaction in Nuclear Beta Decay and G-Parity Nonconservation

Abstract

The pseudoscalar in weak interactions is induced by the lepton-pair decay of the pion emitted from the nucleon. In· muon capture reactions, the strength of this interaction is given by mfp~8fA, theoretically as well as experimentallyY A possible effect of this interaction in nuclear beta decays m,ay be very small, since its effective strength is reduced by a factor 206 compared with that of the muon capture reactions. Recently, a detailed investigation of this problem was required, since the induced pseudoscalar interaction may affect the beta-ray angular distribution in polarized nuclei, and the pseudoscalar may bring an ambiguity for determining the strength of the second-class induced tensor interaction, which violates the G-parity conservation in the axial vector current.2>,s> We show here that there is no such ambiguity remammg, by calculating the particle parameters in the theory of beta decay explicitly. There are extensive investigations for the particle p~rameters by taking into account the induced effects,3> Coulomb1>, 4>7> and radiative8> corrections, and higher order nuclear matrix elements which come from the p and d waves of the leptons,1>, 4>-7> except for the induced pseudoscalar interaction. Here we give· the explicit forms for the particle parameters, which should be added to those given in the published formulasY• 4> -7> We adopt, therefore, the same notation as in the previous publications, and also the units h=me=c=l. We discuss the allowed transition only. We assume the interaction Hamiltonian density,