학술논문
First Observation of $P$-odd $\gamma$ Asymmetry in Polarized Neutron Capture on Hydrogen
Document Type
Working Paper
Author
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.
Source
Phys. Rev. Lett. 121, 242002 (2018)
Subject
Language
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 $\Delta I=1$, \mbox{$^{3}S_{1}\rightarrow {^{3}P_{1}}$} 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 EFT. We measured $A^{np}_\gamma = [-3.0 \pm 1.4 (stat) \pm 0.2 (sys)]\times 10^{-8}$, which implies a DDH weak $\pi NN$ coupling of $h_{\pi}^{1} = [2.6 \pm 1.2(stat) \pm 0.2(sys)] \times 10^{-7}$ and a pionless EFT constant of $C^{^{3}S_{1}\rightarrow ^{3}P_{1}}/C_{0}=[-7.4 \pm 3.5 (stat) \pm 0.5 (sys)] \times 10^{-11}$ MeV$^{-1}$. We describe the experiment, data analysis, systematic uncertainties, and the implications of the result.
Comment: 6 pages, 5 figures
Comment: 6 pages, 5 figures