Grant: Subatomic Physics Envelope - Project

<p>  Nuclear beta decay correlation experiments helped establish the nature of the weak interaction, a theory with spin-1 bosons coupling only to left-handed leptons. Such measurements can assist particle physics by determining 1st-generation lepton-quark couplings of possible new particles, but must reach excellent accuracy of 0.1% with high significance. Using atom trap technology, we are poised to complete two sets of experiments reaching this accuracy.<br /> Confined in a 1 mm-sized cloud, the nuclei undergo beta decay, producing three products: a positron, a neutrino, and a recoiling daughter nucleus. The daughter nucleus has very little kinetic energy and would stop in a nm of material, but it freely escapes the trap. By detecting it in coincidence with the positron, we can measure the momentum and angular distribution of neutrinos. <br />    We have learned to spin-polarize nuclei, and measuring the polarization of the decaying species by atomic methods independent of the nuclear decays. One Texas A&M Ph.D. student is writing up data from 2012 on the beta asymmetry at 1-2% accuracy, allowing discrimination between theories of isospin mixing in 37K, while one Canadian and one U.S. student are analyzing the more accurate data we have taken this year on several observables at 0.5% accuracy. We plan another series of runs with improvements on the present apparatus to improve to 0.1% accuracy and be complementary to high and medium-energy physics experiments.<br />    We also would improve our best direct sensitivity to general scalar interactions coupling to the first generation of particles by measuring the beta-neutrino correlation in the pure Fermi decay of a spin-0 nucleus. The complete angular acceptance for recoils we have developed will minimize key systematic errors in our EEC-approved upgrade of this experiment, with a goal of reaching 0.1% accuracy. We determine systematic errors for this experiment from statistics-limited kinematic observables that are independent of the angular correlation.</p> <p>  A new possible source of time-reversal violation contributes to the radiative decay of 37K. The correlation between beta, neutrino, and radiative gamma momenta is independent of spin, and therefore free of constraints from electric dipole moments. We intend to add low-energy gamma detectors to the present apparatus and start measurements in this 3-year grant period.</p>