Precise Measurement of the β-Asymmetry in the Decay of Magneto-Optically Trapped, Spin-Polarized 37K

Abstract

Precise low-energy measurements in nuclear β-decay provide constraints on possible physics beyond the standard model complementary to high-energy collider experiments. This thesis describes the most precise measurement of the positron asymmetry from a polarized nucleus to date. At the TRIUMF Neutral Atom Trap, atoms of the positron emitter 37K are confined in an alternating-current magneto-optical trap and spin-polarized to 99.13(9)% via optical pumping. The use of atom-trapping techniques allow for an exceptionally open geometry with the decay products escaping the trapping region unperturbed by the trapping potential. The emitted positrons are detected in a pair of symmetric detectors placed along the polarization axis to measure the asymmetry. The analysis was performed blind and considers β-scattering and other systematic effects. The result, Aβ (0) = −0.5707 ± 0.0018, places limits on the mass of a hypothetical W boson coupling to right-handed neutrinos to be > 300GeV/c^2 at zero-mixing as well as contributes to an independent determination of the Vud element of the CKM matrix.