Improved Limit on Tensor Currents in the Weak Interaction from $^8$Li $β$ Decay

Abstract

The electroweak interaction in the Standard Model (SM) is described by a pure vector-axialvector structure, though any Lorentz-invariant component could contribute. In this work, we present the most precise measurement of tensor currents in the low-energy regime by examining the β-ν correlation of trapped 8 Li ions with the Beta-decay Paul Trap. We find a βν = −0.3325±0.0013stat ± 0.0019syst at 1σ for the case of coupling to right-handed neutrinos (CT = −C T ), which is consistent with the SM prediction.