An improved design for the Beta-decay Paul Trap

The Beta-decay Paul Trap (BPT) at Argonne National Laboratory measures the beta-neutrino angular correlation coefficient $a_{\beta \nu}$ in the pure Gamow-Teller decay of $^{8}$Li and $^{8}$B (decaying to $^{8}$Be$^* \rightarrow 2 \alpha$) to search for a tensor component of the weak interaction. The BPT has an ultimate measurement goal of 0.1% uncertainty in $a_{\beta \nu}$. Currently, the largest source of systematic uncertainty is the radiative and recoil order term corrections of the decays, which come from theory. These recoil order terms can be measured to constrain the theory corrections, but this requires a complete kinematic reconstruction of the decays. Therefore, a key source of experimental systematic uncertainty is the scattering of the emitted betas on the trap structure, hindering the kinematic reconstructions to measure these recoil order terms. In order to reduce beta scattering by a factor of 3, the existing rectangular BPT electrodes will be replaced by thin wires that approximate a quadrupole potential near the center of the trap. This new design will also reduce the required RF voltage by 30%, improving the resolution of the silicon detectors used in the experiment by reducing pick-up on them. The new design and supporting simulations will be presented.