Tensor interaction limit derived from the α-β-ν[over ¯] correlation in trapped 8Li ions

Improved Tensor Current Limit from ^{8}B β Decay Including New Recoil-Order Calculations

A precision measurement of the β^{+} decay of ^{8}B was performed using the Beta-decay Paul Trap to determine the β-ν angular correlation coefficient a_{βν}. 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_{βν}=-0.3345±0.0019_{stat}±0.0021_{syst}. This value agrees with the standard model value of -1/3 and improves uncertainties in ^{8}B by nearly a factor of 2. By combining results from ^{8}B and ^{8}Li, a tight limit on tensor current coupling to right-handed neutrinos was obtained. A recent global evaluation of all other precision β decay studies suggested a nonzero value for right-handed neutrino coupling in contradiction with the standard model at just above 3σ. The present results are of comparable sensitivity and do not support this finding.

Angular Correlations in the β Decay of ^{8}B: First Tensor-Current Limits from a Mirror-Nucleus Pair

We present the first measurement of the α-β-ν angular correlation in the Gamow-Teller β^{+} decay of ^{8}B. This was accomplished using the Beta-decay Paul Trap, expanding on our previous work on the β^{-} decay of ^{8}Li. The ^{8}B result is consistent with the V-A electroweak interaction of the standard model and, on its own, provides a limit on the exotic right-handed tensor current relative to the axial-vector current of |C_{T}/C_{A}|^{2}<0.013 at the 95.5% confidence level. This represents the first high-precision angular correlation measurements in mirror decays and was made possible through the use of an ion trap. By combining this ^{8}B result with our previous ^{8}Li results, we demonstrate a new pathway for increased precision in searches for exotic currents.

Impact of Clustering on the ^{8}Li β Decay and Recoil Form Factors

We place unprecedented constraints on recoil corrections in the β decay of ^{8}Li, by identifying a strong correlation between them and the ^{8}Li ground state quadrupole moment in large-scale ab initio calculations. The results are essential for improving the sensitivity of high-precision experiments that probe the weak interaction theory and test physics beyond the standard model. In addition, our calculations predict a 2^{+} state of the α+α system that is energetically accessible to β decay but has not been observed in the experimental ^{8}Be energy spectrum, and has an important effect on the recoil corrections and β decay for the A=8 systems. This state and an associated 0^{+} state are notoriously difficult to model due to their cluster structure and collective correlations, but become feasible for calculations in the ab initio symmetry-adapted no-core shell-model framework.

Improved Limit on Tensor Currents in the Weak Interaction from ^{8}Li β Decay

The electroweak interaction in the standard model is described by a pure vector-axial-vector structure, though any Lorentz-invariant component could contribute. In this Letter, we present the most precise measurement of tensor currents in the low-energy regime by examining the β-ν[over ¯] correlation of trapped ^{8}Li ions with the Beta-decay Paul Trap. We find a_{βν}=-0.3325±0.0013_{stat}±0.0019_{syst} at 1σ for the case of coupling to right-handed neutrinos (C_{T}=-C_{T}^{'}), which is consistent with the standard model prediction.

Limit on Tensor Currents from ^{8}Li β Decay

In the standard model, the weak interaction is formulated with a purely vector-axial-vector (V-A) structure. Without restriction on the chirality of the neutrino, the most general limits on tensor currents from nuclear β decay are dominated by a single measurement of the β-ν[over ¯] correlation in ^{6}He β decay dating back over a half century. In the present work, the β-ν[over ¯]-α correlation in the β decay of ^{8}Li and subsequent α-particle breakup of the ^{8}Be^{*} daughter was measured. The results are consistent with a purely V-A interaction and in the case of couplings to right-handed neutrinos (C_{T}=-C_{T}^{'}) limits the tensor fraction to |C_{T}/C_{A}|^{2}<0.011 (95.5% C.L.). The measurement confirms the ^{6}He result using a different nuclear system and employing modern ion-trapping techniques subject to different systematic uncertainties.

In-trap spectroscopy of charge-bred radioactive ions

In this Letter, we introduce the concept of in-trap nuclear decay spectroscopy of highly charged radioactive ions and describe its successful application as a novel spectroscopic tool. This is demonstrated by a measurement of the decay properties of radioactive mass A=124 ions (here, ^{124}In and ^{124}Cs) in the electron-beam ion trap of the TITAN facility at TRIUMF. By subjecting the trapped ions to an intense electron beam, the ions are charge bred to high charge states (i.e., equivalent to the removal of N-shell electrons), and an increase of storage times to the level of minutes without significant ion losses is achieved. The present technique opens the venue for precision spectroscopy of low branching ratios and is being developed in the context of measuring electron-capture branching ratios needed for determining the nuclear ground-state properties of the intermediate odd-odd nuclei in double-beta (ββ) decay.