Li beta decay recoil form factors*

This work discusses ab initio calculations of recoil form factors in ⁸Li beta decay essential for improving the sensitivity of high-precision experiments that probe the weak interaction theory. We use the symmetry-adapted no-core shell model (SA-NCSM) that utilizes emergent symmetries in nuclei to reduce the dimensionality of the model space, hence making solutions to heavier nuclei and ultra-large model spaces feasible. The large-scale calculations lead to precise prediction of recoil form factors by identifying a strong correlation between them and the ⁸Li ground state quadrupole moment. In addition, our calculations find a 2⁺ state of the alpha + alpha system that is energetically accessible to beta decay but has not been observed in the experimental ⁸Be energy spectrum, and has an important effect on the recoil corrections and decay for the A = 8 systems.