- By:
- Snow, William M; Fry, Jason A; Fomin, Nadia ; Alarcon, Ricardo O; Baessler, Stefan F; Bowman, James D; Birge, Noah W; Calarco, John R; Cianciolo, Thomas ; Chupp, Timothy E; Coppola, Christopher E; Crawford, Christopher B; Craycraft, Kayla L; Garishvili, Irakli ; Gericke, Michael T; Grammer, Kyle B; Greene, Geoffrey L; Hamblen, Joshua B; Hayes, Christopher B; Iverson, Erik B; Mahurin, Robert S; Mueller, Paul E; Musgrave, Matthew M; Novikov, Ivan S; Penttila, Seppo I; Pocanic, Dinko ; Salas Bacci, Americo F; Scott, Elizabeth M; Sprow, Aaron P; Tang, Zhaowen ; Tong, Xin ; Whitehead, Ryan A; Wilburn, Wesley S
- Journal Name:
- Physical Review Letters
- Page Number:
- 1-6
- Volume:
- 121
- Issue Number:
- 242002
- Publication Date:
- June 20, 2025
- View DOI Listing:
- https://doi.org/10.1103/PhysRevLett.121.242002
Abstract
We report the first observation of the parity-violating 2.2 MeV gamma-ray asymmetry A^(np)_gamma 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^(np)_gamma isolates the Delta I = 1, ^3S_1-> ^3P_1 component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to the weak coupling constant h^1_pi in the DDH meson exchange model and to a low energy constant C^[^3S_1 ->^3P_1]/C_0 in pionless effective field theory. We measured A^(np)_gamma = (-3.0 +/-1.4(stat.)+/-0.2(sys.))x10e-8, which implies a DDH weak NN coupling of h^1_pi = (3.1+/-1.5)x10e-7 and a pionless EFT constant of C^[^3S_1->^3P_1]/C_0 = (-5.2+/-2.4)x10e-10 MeV^(-1). We describe the experiment, data analysis, systematic uncertainties, and the implications of the result.
