Polarization probe for beta-decaying atoms

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Using the TRIUMF Neutral Atom Trap (TRINAT), we seek part per thousand accuracy of several angular correlations in the beta decay of spin-polarized 37K, to search for new interactions not in the standard model. Such accuracy would be competitive with the best planned searched in neutron beta decay, and explore physics beyond the Standard Model at scales set by M_W/(accuracy)**1/2 or about 2 TeV, complementary to the LHC. A test experiment at 2% accuracy has identified several areas to be improved, most covered under the project grant. Many weak decay experiments are limited by the knowledge of the absolute polarization of the decaying species. We measure the polarization of the decaying 37K atoms in situ by a non-destructive atomic technique that photoionizes and collects a small fraction of the unpolarized atoms. The technique worked in the earlier published experiment at 2% statistical accuracy, but we have improved the polarization greatly, so there are many fewer unpolarized atoms to probe. This grant is for a photoionization laser that can be pulsed on demand, which will let us probe at advantageous times during the polarization cycle, improving our signal/noise about two orders of magnitude. This will let us achieve our design sensitivity. Otherwise the knowledge of the polarization would become our limiting systematic error. It will also let us directly image the distribution of atoms while polarized, eliminating another important systematic error. A related request is for 3 large-area microchannel plates, common spares for the ion and electron detectors. We are implementing an electron detector inherited by our Texas A&M colleagues, and have used our existing spares to replace those that had deteriorated with time. The large area will let us collect all the atomic electrons-- measurements with a 40 mm detector in December 2012 suggest some are at higher energy-- while the position sensitivity will help signal/noise on the photoelectron diagnostic. The techniques will continue to be used and optimized by our present Ph.D. student and by co-op and summer undergrads learning multidisciplinary atomic, laser, and particle detection techniques. The scale of the photoionization parts of the experiment have provided a good place for undergrad participation in the past, since the optics simply requires patience, and the atomic physics involves extending textbook quantum mechanics.