Arizona State University, Tempe, Arizona 85287, USA.
High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
Phys Rev Lett. 2018 Dec 14;121(24):242002. doi: 10.1103/PhysRevLett.121.242002.
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.
我们首次观察到使用极化冷中子入射液氘靶在橡树岭国家实验室散裂中子源中进行的中子-质子俘获的宇称破坏γ射线不对称性 A_{γ}^{np}。A_{γ}^{np} 分离出弱核子-核子相互作用的 ΔI=1, ^{3}S_{1}→^{3}P_{1} 分量，该分量主要由介子交换主导，并且可以直接与 DDH 介子交换模型或无π有效场论中的单个耦合常数相关联。我们测量到 A_{γ}^{np}=[-3.0±1.4(stat)±0.2(syst)]×10^{-8}，这意味着 DDH 弱πNN 耦合 h_{π}^{1}=[2.6±1.2(stat)±0.2(syst)]×10^{-7}，以及无π有效场论常数 C^{^{3}S_{1}→^{3}P_{1}}/C_{0}=[-7.4±3.5(stat)±0.5(syst)]×10^{-11} MeV^{-1}。我们描述了实验、数据分析、系统不确定性以及结果的意义。
