Measurement of the Correlation between Nuclear Alignment and Electron Direction inB12Decay as a Direct Search for the Second-Class Axial-Vector Current

Abstract

The alignment correlation term $A{\ensuremath{\alpha}}_{\ensuremath{-}}E{P}_{2}(cos\ensuremath{\theta})$ has been measured in the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay $^{12}\mathrm{B}$ \ensuremath{\rightarrow} $^{12}\mathrm{C}$(g.s.) by a novel technique. The result, ${\ensuremath{\alpha}}_{\ensuremath{-}}({E}_{0})=\ensuremath{-}\frac{(0.1\ifmmode\pm\else\textpm\fi{}0.2)}{\mathrm{GeV}}$, indicates that the conserved vector current weak-magnetism form factor, ${F}_{M}$, is essentially compensated here by the weak electricity (induced tensor) form factor ${F}_{E}$. Using the decomposition of ${F}_{E}={{F}_{E}}^{(1)}+{{F}_{E}}^{(2)}$ into first- and second-class parts, as well as a reliable estimate of ${{F}_{E}}^{(1)}$, we conclude that ${{F}_{E}}^{(2)}$ is small compared to ${F}_{M}$, and compatible with zero.