Toward precision D coefficient measurement in polarized neutron decay and the development of A helium-3 neutron polarizer.

Abstract

I describe the search for possible time reversal symmetry violation by measurement of the coefficient D in polarized neutron decay. This relates to the triple product among the neutron polarization vector, electron momentum, and proton momentum in the neutron decay rate $(w\sim{-}\\sigma\sb{n}\cdot(\vec p\sb{e}\times\vec p\sb{p})).$ With the improvements in neutron polarization (97%), an optimal octagonal detector geometry, and neutron spin transport system, about $15\times10\sp6$ decay events were selected from data acquired at the Cold Neutron Research Facility at NIST, Gaithersburg. I have developed techniques for extracting D from the positive and negative triple product decay rates. My preliminary result is $D=(12.1\pm13.4)\times10\sp{-4}$ where the uncertainty is statistical only. The false D resulting from the instrumental factor $(\sigma\sb{\kappa})$ and neutron polarization uncertainty $(\sigma\sb{P})$ are negligible. I also estimate the false D of the asymmetric transverse polarization (ATP) effect with an upper limit $5\times10\sp{-4}$ for the preliminary analysis of the initial data. I also describe development of an optical pumping/spin exchange neutron spin filter and obtained 40% neutron polarization for 2 A neutrons with a 10 amagat-cm 35 cm$\sp3$ polarized $\sp3$He cell.