Improved Limit on Tensor Currents in the Weak Interaction from Li-8 beta Decay

The electroweak interaction in the standard model is described by a pure vector-axial-vector structure, though any Lorentz-invariant component could contribute. In this Letter, we present the most precise measurement of tensor currents in the low-energy regime by examining the beta-(nu) over bar correlation of trapped Li-8 ions with the Beta-decay Paul Trap. We find a(beta nu) = -0.3325 +/- 0.0013(stat) +/- 0.0019(syst) at 1 sigma for the case of coupling to right-handed neutrinos (C-T = -C-T'), which is consistent with the standard model prediction.