A precision measurement of the ${\beta }^{+}$ decay of ${}^8\mathrm{B}$ was performed using the Beta-decay Paul Trap to determine the $\beta \text{−}\nu$ angular correlation coefficient $a_{\beta \nu }$. The experimental results were combined with new ab initio symmetry-adapted no-core shell-model calculations to yield the second-most precise measurement from Gamow-Teller decays, $a_{\beta \nu }=-0.3345\pm 0.0019_{\mathrm{stat}}\pm 0.0021_{\mathrm{syst}}$. This value agrees with the standard model value of $-1/3$ and improves uncertainties in ${}^8\mathrm{B}$ by nearly a factor of 2. By combining results from ${}^8\mathrm{B}$ and ${}^8\mathrm{Li}$, a tight limit on tensor current coupling to right-handed neutrinos was obtained. A recent global evaluation of all other precision $\beta$ decay studies suggested a nonzero value for right-handed neutrino coupling in contradiction with the standard model at just above $3\sigma$. The present results are of comparable sensitivity and do not support this finding.

Atomic masses are a foundational quantity in our understanding of nuclear structure, astrophysics, and fundamental symmetries. The longstanding goal of creating a predictive global model for the binding energy of a nucleus remains a significant challenge, however, and prompts the need for precise measurements of atomic masses to serve as anchor points for model developments. We present precise mass measurements of neutron-rich Ru and Pd isotopes performed at the Californium Rare Isotope Breeder Upgrade facility at Argonne National Laboratory using the Canadian Penning Trap mass spectrometer. The masses of ${}^{108}\mathrm{Ru}, {}^{110}\mathrm{Ru}$, and ${}^{116}\mathrm{Pd}$ were measured to a relative mass precision $\delta m/m\approx {10}^{-8}$ via the phase-imaging ion-cyclotron-resonance technique, and represent an improvement of approximately an order of magnitude over previous measurements. These mass data were used in conjunction with the physically interpretable machine learning (PIML) model, which uses a mixture density neural network to model mass excesses via a mixture of Gaussian distributions. The effects of our new mass data on a Bayesian-updating of a PIML model are presented.

Neutrinoless double beta decay ($0\nu \beta \beta$) provides a way to probe physics beyond the Standard Model of particle physics. The upcoming nEXO experiment will search for $0\nu \beta \beta$ decay in ¹³⁶Xe with a projected half-life sensitivity exceeding ${10}^{28}$ years at the 90% confidence level using a liquid xenon (LXe) Time Projection Chamber (TPC) filled with 5 tonnes of Xe enriched to ∼90% in the $\beta \beta$-decaying isotope ¹³⁶Xe. In parallel, a potential future upgrade to nEXO is being investigated with the aim to further suppress radioactive backgrounds and to confirm $\beta \beta$-decay events. This technique, known as Ba-tagging, comprises extracting and identifying the $\beta \beta$-decay daughter ¹³⁶Ba ion. One tagging approach being pursued involves extracting a small volume of LXe in the vicinity of a potential $\beta \beta$-decay using a capillary tube and facilitating a liquid-to-gas phase transition by heating the capillary exit. The Ba ion is then separated from the accompanying Xe gas using a radio-frequency (RF) carpet and RF funnel, conclusively identifying the ion as ¹³⁶Ba via laser-fluorescence spectroscopy and mass spectrometry. Simultaneously, an accelerator-driven Ba ion source is being developed to validate and optimize this technique. The motivation for the project, the development of the different aspects, along with the current status and results, are discussed here.