Comparison of the Beta-Alpha Angular Correlations in the Li8 and B8 Beta Decays, and the Conserved Vector Current Theory

This paper describes a comparison of the beta-alpha angular correlations of the beta decays of ${\mathrm{Li}}^{8}$ and ${\mathrm{B}}^{8}$ to the 2.90-Mev alpha-unstable level of ${\mathrm{Be}}^{8}$. The data were fitted to an angular correlation in the laboratory system of the form $W({\ensuremath{\theta}}_{\ensuremath{\beta}\ensuremath{\alpha}})=1+A{cos\ensuremath{\theta}}_{\ensuremath{\beta}\ensuremath{\alpha}}+B{{cos}^{2}\ensuremath{\theta}}_{\ensuremath{\beta}\ensuremath{\alpha}}$, where $A$ and $B$ were independently determined for the ${\mathrm{Li}}^{8}$ and ${\mathrm{B}}^{8}$ beta decays from measurements at ${\ensuremath{\theta}}_{\ensuremath{\beta}\ensuremath{\alpha}}=0\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, \mathrm{and} 180\ifmmode^\circ\else\textdegree\fi{}$. The coefficients $A$ are due to the recoil of ${\mathrm{Be}}^{8*}$ and have the same sign for both beta decays. The coefficients $B$ arise from the interference of forbidden vector matrix elements with the allowed axial vector matrix element and have different signs in the two decays. The correlation for the ${\mathrm{Li}}^{8}$ decay was measured with average total beta energies, ${W}_{\ensuremath{\beta}}\ensuremath{\simeq}5, 8, \mathrm{and} 11$ Mev. Both $A$ and $B$ were found to be approximately linear in ${W}_{\ensuremath{\beta}}$. The correlation for the ${\mathrm{B}}^{8}$ decay was measured only with average ${W}_{\ensuremath{\beta}}\ensuremath{\simeq}11$ Mev. From the data with ${W}_{\ensuremath{\beta}}\ensuremath{\simeq}11$ Mev, the difference of the coefficients, $B({\mathrm{Li}}^{8})\ensuremath{-}B({\mathrm{B}}^{8})$, equals $(0.0070\ifmmode\pm\else\textpm\fi{}0.0012){W}_{\ensuremath{\beta}}$. This result is compared with theoretical predictions based on the older Fermi and the newer conserved vector current theories of beta decay. The experiment agrees with the prediction of the latter theory.