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Blyth, D; Fry, J; Fomin, N; Alarcon, R; Alonzi, L; Askanazi, E; Baeßler, S; Balascuta, S; Barrón-Palos, L; Barzilov, A; Bowman, J D; Birge, N; Calarco, J R; Chupp, T E; Cianciolo, V; Coppola, C E; Crawford, C B; Craycraft, K; Evans, D; Fieseler, C; Frlež, E; Garishvili, I; Gericke, M T W; Gillis, R C; Grammer, K B; Greene, G L; Hall, J; Hamblen, J; Hayes, C; Iverson, E B; Kabir, M L; Kucuker, S; Lauss, B; Mahurin, R; McCrea, M; Maldonado-Velázquez, M; Masuda, Y; Mei, J; Milburn, R; Mueller, P E; Musgrave, M; Nann, H; Novikov, I; Parsons, D; Penttilä, S I; Počanić, D; Ramirez-Morales, A; Root, M; Salas-Bacci, A; Santra, S; Schröder, S; Scott, E; Seo, P-N; Sharapov, E I; Simmons, F; Snow, W M; Sprow, A; Stewart, J; Tang, E; Tang, Z; Tong, X; Turkoglu, D J; Whitehead, R; Wilburn, W S
Physical review letters, 2018-Dec-14, Volume: 121, Issue: 24Journal Article
We report the first observation of the parity-violating gamma-ray asymmetry A_{γ}^{np} in neutron-proton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. A_{γ}^{np} isolates the ΔI=1, ^{3}S_{1}→^{3}P_{1} component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless effective field theory. We measured A_{γ}^{np}=-3.0±1.4(stat)±0.2(syst)×10^{-8}, which implies a DDH weak πNN coupling of h_{π}^{1}=2.6±1.2(stat)±0.2(syst)×10^{-7} and a pionless EFT constant of C^{^{3}S_{1}→^{3}P_{1}}/C_{0}=-7.4±3.5(stat)±0.5(syst)×10^{-11} MeV^{-1}. We describe the experiment, data analysis, systematic uncertainties, and implications of the result.
