The G-parity-violating, second-class current- (SCC) induced tensor term in the weak-nucleon axial-vector current was determined from β-decay correlation measurements of the mass A = 20 mirror pair. The alignment correlation terms in the β-decay angular distribution from the purely spin aligned mirror pair, 20F and 20Na, were measured in the present study. Combining the present results with existing results of β and delayed γ-ray angular correlation measurements for the A = 20 mirror pair, the SCC-induced tensor term was extracted to be dII/Ac = 0.18 ± 0.48. In the extraction, the weak-magnetism term, b/Ac = 8.58 ± 0.28, evaluated from the M1 analog γ-ray decay strength, was used in a framework of the conserved vector current hypothesis. This is the first unambiguous extraction of the (b-dII)/Ac term free from the contribution of the second-forbidden form factor, j2, in the axial-vector current, which was a limiting factor for accurate determination of nonexistence of the SSC in the β decay of the A = 20 system.
ASJC Scopus subject areas
- Nuclear and High Energy Physics