Tensor Interaction Limit Derived From The Alpha-Beta-(Nu)Over-Bar Correlation In Trapped Li-8 Ions

A measurement of the alpha-beta-(nu) over bar angular correlation in the Gamow-Teller decay Li-8 -> Be-8* + (nu) over bar + beta, Be-8* -> alpha + alpha has been performed using ions confined in a linear Paul trap surrounded by silicon detectors. The energy difference spectrum of the alpha particles emitted along and opposite the direction of the beta particle is consistent with the standard model prediction and places a limit of 3.1% (95.5% confidence level) on any tensor contribution to the decay. From this result, the amplitude of any tensor component C-T relative to that of the dominant axial-vector component C-A of the electroweak interaction is limited to vertical bar C-T/C-A vertical bar < 0.18 (95.5% confidence level). This experimental approach is facilitated by several favorable features of the Li-8 beta decay and has different systematic effects than the previous beta-<(nu)over bar> correlation results for a pure Gamow-Teller transition obtained from studying He-6 beta decay. DOI: 10.1103/PhysRevLett.110.092502