Limit on Tensor Currents from 8Li β Decay

In the standard model, the weak interaction is formulated with a purely vector-axial-vector (V-A) structure. Without restriction on the chirality of the neutrino, the most general limits on tensor currents from nuclear beta decay are dominated by a single measurement of the beta-(nu) over bar correlation in He-6 beta decay dating back over a half century. In the present work, the beta-(nu) over bar-alpha correlation in the beta decay of Li-8 and subsequent alpha-particle breakup of the Be-8* daughter was measured. The results are consistent with a purely V-A interaction and in the case of couplings to right-handed neutrinos (C-T = -C'(T)) limits the tensor fraction to vertical bar C-T/C-A vertical bar(2) < 0.011 (95.5% C.L.). The measurement confirms the He-6 result using a different nuclear system and employing modern ion-trapping techniques subject to different systematic uncertainties.