β-decay asymmetries in polarized B12 and N12 and the G-parity-nonconserving weak interaction

The decay asymmetries (a) in polarized B12 and N12 have been measured as a function of β-ray energy (E). The coefficients α, in a form of a=P(pE)(1+αE), have been determined to be α-(B12)=+(0.31±0.06)%/MeV and α+(N12)=-(0.21±0.07)%/MeV. The experimental value, α - α+=(0.52±0.09)%/MeV. is larger than the prediction of conserved-vector-current theory, (α - α+)CVC0.27%/MeV, and in favor of the existence of the second-class induced-tensor current.