Precision β − ν correlation measurements with the Beta-decay Paul Trap

The Beta-decay Paul Trap (BPT) at Argonne National Laboratory has proven to be an extremely effective tool for high-precision tests of the Standard Model via measurements of the β − ν correlation in mass-8 isotopes. Using four double-sided silicon strip detectors (DSSDs) backed by plastic scintillators and surrounding the ions confined by the BPT, the kinematics of the decays of the mirror nuclei lithium-8 and boron-8 are overdetermined when all charged decay products are measured. The most stringent low-energy limit on an intrinsic tensor current in the weak interaction was set using the BPT in 2015 (Sternberg, M.G., et al., Phys. Rev. Lett. 115, 182501 2015) utilizing trapped lithium-8. Since then, similar data for boron-8 and higher statistics data for lithium-8 have been collected and are currently being analyzed. With the elimination of radio-frequency (RF) pickup from the DSSDs and a detailed investigation of experimental systematic errors, the uncertainty is now dominated by the contribution from recoil-order terms in the decay rate. Our eventual goal is to limit tensor currents in the weak interaction with relative precision at or below 0.1%.