Grant: Subatomic Physics Envelope - Project

The standard model of the weak interaction united it with electromagnetism by using currents with similar Lorentz transformations, naturally adding terms that produce extreme lepton helicity to match experiment. The resulting elegant Lagrangian completely breaks parity symmetry, with no particular underlying reason-- e.g. no apparent importance to early-universe cosmology. So it's natural to ask whether parity is truly completely broken in beta decay. Electrons, of course, can have either handedness in nature, so it remains a puzzle that the weak interaction only couples to one of them, while right-handed neutrinos would make neutrinos a completely different type of lepton. We will show how different helicities change the angular distributions of the particles emitted in beta decay. With TRIUMF's atom trap for beta decay (TRINAT) in this grant period we plan to complete an upgraded measurement of the angular distributions of polarized 37K, an isobaric analog decay with very similar initial and final nuclear wavefunctions. We've made a number of technical improvements of our 99.1 +- 0.1% spin polarization, with goal of improving our best nuclear beta asymmetry measurement by factors of 3-5, and extending our measurements to the asymmetry of the recoil nuclei, which would compete directly with the LHC channel p + p -> e + nu to search for unknown interactions. This is the thesis of an existing Ph.D. student, and would provide a dedicated observable for an additional 2-year postdoc. We would complete a 1st measurement of a time-reversal violation experiment in radiative beta decay, which would be unique to the 1st generation of particles. It would be the thesis of a new direct-to-Ph.D. grad student we are trying to recruit. We would then decide whether to pursue an upgraded apparatus via Year 2 RTI. We are working towards a test of time reversal symmetry in the isospin-forbidden decay of 47K, which theoretically has greatly enhanced sensitivity to time-reversal breaking interactions in the progeny nucleus. We would first measure the isospin mixing to determine the enhancement. Our finished measurements of the neutrino spectrum of fission product 92Rb are in agreement with expectations, suggesting such 0- to 0+ decays are not part of the high-energy discrepancy between measured and modelled reactor neutrino spectra. Grad students design, complete, analyze, and interpret entire experiments. Co-op undergrads help with non-critical path atomic experiments where they can fully appreciate the underlying physics while being exposed to the subatomic physics. There are many straightforward and natural ways implemented to consider any interested budding physicist for all positions to ensure the best match-- the TRIUMF student ads have an exemplary open invitation, and the PI feels honored to read every cover letter's story and considers all CV's.