Beta Decay with Laser Traps: Search for Scalars

Lasers can be used to cool and trap neutral atoms. Such techniques won the 1997 Nobel Prize for Chu, Phillips, and Cohen-Tannoudji, and are revolutionizing a number of subfields of atomic physics. At TRIUMF, we are applying these techniques to a rather different problem, the study of nuclear beta decay. We use a Magneto-Optical Trap to capture beta-decaying nuclei and hold them suspended in space, free of any backing materials. By detecting the low-energy nuclear recoils in coincidence with the beta, we can reconstruct the neutrino momentum. The angular distribution of the neutrinos with respect to the beta direction is predicted by the Standard Model, and deviations from that prediction are sensitive to new interactions. We are also learning to use these atomic techniques to polarize nuclei to test whether parity is maximally violated in the charged weak interaction. Preliminary measurements of the beta-neutrino angular distribution from a spin-0 nucleus will be shown: our goal is to set limits on the existence of new scalar bosons complementary to those set by high-energy colliders.