Asymmetry of Beta-Ray Angular Distribution in Polarized 12B and 12N and Second-Class Current

Abstract

An explicit formula for beta-ray angular distribution in the decay of polarized nuclei is given by taking into account the radiative corrections, Coulomb corrections of the finite-size nucleus, weak magnetisim, induced pseudoscalar, second-class induced tensor, and contributions of the d-wave leptons. Generally speaking, the radiative corrections are almost the same for P0 (cosθ) and P1 (cosθ) terms. In particular, the logarithmic divergence disappears for the asymmetry factor in the case of the Gamow-Teller transitions. And the effect of the induced pseudoscalar current is extremely small. Experimental data on the beta decays of polarized 12B and 12N are carefully investigated, and it is shown that these data are in favor of the existence of the second-class induced tensor current. Contributions of the ∫(σ·r)r and ∫σr2 terms, which are evaluated with available nuclear models, are found to be negligible. The effect of the exchange currents is also discussed in connection with the elementary particle treatment of the nuclear beta decay.