Improving spin-polarized beta-neutrino correlations

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Using TRIUMF's atom trap for nuclear beta decay (TRINAT), we have measured the beta asymmetry with respect to the nuclear spin in 37K to be -0.5706+-0.0018. Our 0.32% accuracy is the best achieved in any beta asymmetry measurement in a nucleus or the neutron, and is in agreement with the prediction of the Standard Model of particle physics. The first beta asymmetry was measured in 1957 by C.S. Wu of Columbia University and collaborators, and was a major confirmation of the prediction that parity was violated in the weak interaction. It is presently believed that parity is completely broken-- e.g. all known neutrinos are `left-handed', with spin circulation opposite the direction of motion. To be helpful for present-day tests of the Standard Model, much better accuracy must be reached. Our measurement can be used to separately constrain much new physics, and we show constraints competing favorably with other beta decay measurements. We also show that we need improvements to complement high-energy physics by probing couplings of new boson particles to the first-generation up and down quarks involved in nuclear beta decay. We seek to increase the spin polarization and its known accuracy 0.9913+-0.0009 with better optics for the circularly polarized light; coupled with other improvements such as thin-substrate mirrors (using TRINAT project grant), we would improve our accuracy in the beta asymmetry another factor of 3-5. We also seek improvements to in-vacuum ion detection instrumentation to enable a new and complementary experiment on the spin asymmetry of the recoiling nuclei in singles, along with a particular beta-recoil coincidence observable that has very little sensitivity to theoretical corrections. The recoil asymmetry with respect to the nuclear spin would have very high statistics, and holds the promise of an order of magnitude improvement in sensitivity over existing beta decay measurements to certain types of interactions. Our new Canadian M.Sc. student would implement this equipment for an instrumental M.Sc., which should lead to a Ph.D. project on these experiments. Two equipment items would support a further Ph.D. project on the upgrade of our world-best beta-neutrino correlation measurement in unpolarized 38mK decay. We continue to provide opportunities to one undergrad at a time to help us develop the instrumentation and learn the background physics.