Recoil Asymmetry in β⁺ Decay of Polarized ³⁷K

Most measurements of nuclear beta decay are in agreement with the charged part of the standard model’s weak interaction. The Lagrangian for the W-boson exchange between quarks and leptons produce only one chirality of leptons and antileptons, leading directly to interactions between nucleons and leptons that Lorentz transform like vectors (as in electromagnetism) and axial vectors that depend on spin. The angular distributions of the recoiling product of spin polarized nuclei are sensitive to new interactions that have other Lorentz transformations. The TRIUMF Neutral Atom Trap (TRINAT) was used to laser trap and polarize ³⁷K, with a nuclear polarization in excess of 99%. The delayed recoiling ion coincident with atomic shake-off electrons was collected in a uniform E-field incident on opposing position/time-of-flight sensitive micro-channel plate detectors. Using the recoil asymmetry A_recoil α - (A_β + B_ν), where A_β and B_ν are the beta and neutrino correlation parameters, we present our first results towards constraints on Lorentz tensor and scalar couplings, which we project to be complementary to other particle physics experiments.