Grant: Subatomic Physics Envelope - Research Tools and Instruments

The TRIUMF neutral atom trap lets us detect very low-energy nuclei recoiling from the beta decay of laser-cooled and trapped radioactive atoms. By measuring coincidences with the energetic electrons, we can measure the neutrino momentum event-by-event. With modern atomic techniques, we can also achieve very high known spin polarizations and measure the polarization in situ of the decaying atoms. We have published a measurement of the asymmetry in direction of the neutrino with respect to the nuclear spin of 37K, a well-understood nuclear decay with a half-life of 1.23 sec. We seek to upgrade this experiment to 0.1% accuracy to become competitive with the best neutron beta decay measurements, and complementary to the best muon decay experiments. This will test our knowledge of the charged weak interaction in the Standard Model, which is explained purely by spin-1 W bosons coupling only to left-handed neutrinos. To fix our main systematic errors, we must turn off the magnetic field of our trap faster and with high extinction. We have to turn off the trap to spin-polarize the atoms. Doing this faster will let us count with faster duty cycles to keep the atoms from expanding so we will know better where the decays originate. Higher extinction will let us improve the spin polarization. To do this, we have developed a so-called ""AC MOT"", following development of a group at Manchester U. We must now drive larger coils for our upgraded experiment, and seek larger amplifiers to do this. The AC MOT development has had 4 co-op work terms so far. The AC MOT and optical pumping techniques to improve 41K and 37K polarization is the M.Sc. thesis of a U.B.C. student supervised by the applicant. Polarized observables in 37K decay are the Ph.D. thesis of a Texas A&M student supervised by Texas A&M faculty. We plan to be ready to take data with 37K beam from TRIUMF/ISAC in summer 2011.