First observation of p-odd γ asymmetry in polarized neutron capture on hydrogen

• Main Authors: Musgrave, Matthew (Author), NPDGamma Collaboration (Author)
• Other Authors: Massachusetts Institute of Technology. Laboratory for Nuclear Science (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2020-04-23T20:12:34Z.
• Subjects: Article
• Online Access: Get fulltext

 We report the first observation of the parity-violating gamma-ray asymmetry A[subscript γ under superscript 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[subscript γ under superscript np] isolates the ΔI=1, ³S[subscript 1]→³P[subscript 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[subscript γ under superscript np]=[-3.0±1.4(stat)±0.2(syst)]×10-⁸, which implies a DDH weak πNN coupling of h[subscript π under superscript 1]=[2.6±1.2(stat)±0.2(syst)]×10-⁷ and a pionless EFT constant of [physics equation; see resource]. We describe the experiment, data analysis, systematic uncertainties, and implications of the result. ©2018