Session 1WB: New Directions in Beta Decay I

Nuclear ab initio calculations of 6He β-decay for beyond the Standard Model studies

Precision measurements of β-decay observables offer the possibility to search for deviations from the Standard Model. A possible discovery of such deviations requires accompanying first-principles calculations. We will present a computation of the nuclear structure corrections for the β-decay of ⁶He which is of central interest in several experimental efforts. We employ the impulse approximation together with wave functions calculated using the ab initio no-core shell model with potentials based on chiral effective field theory. We find that nuclear corrections, which we compute within the sensitivity of future experiments, create significant deviation from the naive Gamow-Teller predictions, making their accurate assessment essential in searches for physics beyond the Standard Model.   

Precision Beta-Decay Studies of 8Li and 8B to Constrain Tensor Currents in the Weak Interaction

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. The existence of these exotic S and T currents can then be probed through their effect on various β-decay correlations, such as the β-ν angular correlation coefficient a_βν and the Fierz interference term b_F. The Gamow-Teller β-decays of ⁸Li and ⁸B are ideal to probes to measure a_βν due to their large Q-values and the delayed alpha emission from the excited state ⁸Be, allowing for a detailed measurement of the kinematic shift between the two fragments which can be used to determine a_βν. These measurements were performed with the Beta decay Paul Trap (BPT) at Argonne National Lab. The BPT is surrounded on 4 sides with double-sided silicon strip detectors backed by plastic scintillator detectors, which allow the kinematics of decay products from the trapped mass-8 ions to be over-constrained. In this presentation we will present the recent results from our work in ⁸Li and first results from the decay of ⁸B.