Fenker, Benjamin Brown (2016-11). Precise Measurement of the ?-Asymmetry in the Decay of Magneto-Optically Trapped, Spin-Polarized 37K. Doctoral Dissertation. Thesis uri icon


  • Precise low-energy measurements in nuclear ?-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 ?-scattering and other systematic effects. The result, A? (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.

publication date

  • November 2016