Measurement of the parity violating asymmetry Aγin n⃗+p→d+γ

The weak pion-nucleon coupling constant H π 1 remains poorly determined, despite many years of effort. The recent measurement of the 133 Cs anapole moment has been interpreted to give a value of H π 1 almost an order of magnitude larger than the limit established in the 18 F parity doublet experiments. A measurement of the gamma ray directional asymmetry A γ for the capture of polarized neutrons by hydrogen has been proposed at Los Alamos National Laboratory. This experiment will determine H π 1 independent of nuclear structure effects. However, since the predicted asymmetry is small, A γ ≈5×10 −8 , systematic effects must be reduced to −9 . The design of the experiment will is presented, with an emphasis on the techniques used for controlling systematic errors.