Limit on Tensor Currents from Li8 β Decay

In the standard model, the weak interaction is formulated with a purely vector-axial-vector ($V\text{-}A$) 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 $\beta \text{-}\overline{\nu }$ correlation in ${}^{6}He$ $\beta$ decay dating back over a half century. In the present paper, the $\beta \text{-}\overline{\nu }\text{-}\alpha$ correlation in the $\beta$ decay of ${}^{8}Li$ and subsequent $\alpha$-particle breakup of the ${{}^{8}Be}^{\ast }$ daughter was measured. The results are consistent with a purely $V\text{-}A$ interaction and in the case of couplings to right-handed neutrinos ($C_T=-C_T^{{}^{\prime }}$) limits the tensor fraction to $|C_T/C_A{|}^2<0.011$ (95.5% C.L.). Finally, the measurement confirms the ${}^{6}He$ result using a different nuclear system and employing modern ion-trapping techniques subject to different systematic uncertainties.