A Precision Measurement of the $\beta$-$\nu$ Angular Correlation in $^8$Li with the Argonne $\beta$-decay Paul Trap

Precise measurements of the $\beta$-$\nu$ angular correlation coefficient, $a$, provide information on the presence of possible exotic couplings in the weak interaction. In the $\beta$-decay of $^8$Li to $^8$Be$^*$ and subsequent breakup into two alpha particles, the large Q value and the $\beta$-$\alpha$-$\nu$ correlation provide enhanced sensitivity to any potential tensor coupling. In an initial measurement using the $\beta$-decay Paul Trap (BPT) at Argonne National Laboratory $2 \times 10^{4}$ $\beta$-$\alpha$-$\alpha$ coincidences were detected and a value of $a$ was inferred that places an upper limit of $1.5\%$ on any tensor contribution. The BPT has since been upgraded with improved double-sided silicon strip detectors---including finer segmentation, thinner dead layers, and thicker active silicon---along with new plastic scintillators to kinematically over-determine the decay. We will discuss the results from recent experiments where more than $4 \times 10^{5}$ $\beta$-$\alpha$-$\alpha$ coincidences were measured.