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

TL;DR

This paper reports a highly precise measurement of tensor currents in weak interactions using trapped $^{8}$Li ions, confirming the Standard Model's vector-axial-vector structure and setting new limits on possible tensor contributions.

Contribution

The study provides the most precise low-energy measurement of tensor currents in weak interactions, utilizing the Beta-decay Paul Trap to analyze $^{8}$Li beta decay.

Findings

Measured $a_{\beta\nu} = -0.3325 \pm 0.0013_{stat} \pm 0.0019_{syst}$

Results are consistent with Standard Model predictions

Sets new limits on tensor current contributions in weak interactions

Abstract

The electroweak interaction in the Standard Model (SM) is described by a pure vector-axial-vector 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 $\beta$-$\bar{\nu}$ correlation of trapped $^{8}$Li ions with the Beta-decay Paul Trap. We find $a_{\beta\nu} = -0.3325 \pm 0.0013_{stat} \pm 0.0019_{syst}$ at $1\sigma$ for the case of coupling to right-handed neutrinos $(C_T=-C_T')$, which is consistent with the SM prediction.