Precision Beta-Decay Studies in the Mirror Systems of ⁸Li and ⁸B

The weak interaction of the Standard Model is well-described by a vector-axial vector, or ‘V-A’, structure, which reproduces both maximal parity violation and left-handed neutrinos in beta-decay. However, there is no first-principles reason that other the interactions, such as scalar (S) or tensor (T), may not be present. Tensor currents were searched through a measurement of the beta-neutrino angular correlation coefficient a_bn in the beta-delayed alpha decays of ⁸Li and ⁸B. These decays were studied with the Beta-decay Paul Trap (BPT) at the ATLAS facility of Argonne National Laboratory. The BPT traps a cloud of ions at rest in a volume of ~1 mm³ for extended periods of time, allowing for a backing-free measurement of the emitted particles. The trapping volume is surrounded by segmented, 1mm thick DSSDs, from which the decay kinematics can be fully constrained by a b-a-a triple coincidence measurement. This enables both a nearly background-free measurement of the b-n angular correlation coefficient a_bn. We will present the first measurement of a_bn in 8B and a novel method to constrain C_T and C’_T in the decay of mirror systems.