Measurement of parity-violating γ-ray asymmetry in the capture of polarized cold neutrons on protons

M. T. Gericke, Ricardo Alarcon, S. Balascuta, L. Barrón-Palos, C. Blessinger, J. D. Bowman, R. D. Carlini, W. Chen, T. E. Chupp, C. Crawford, S. Covrig, M. Dabaghyan, N. Fomin, S. J. Freedman, T. R. Gentile, R. C. Gillis, G. L. Greene, F. W. Hersman, T. Ino, G. L. JonesB. Lauss, M. Leuschner, W. R. Lozowski, R. Mahurin, Y. Masuda, J. Mei, G. S. Mitchell, S. Muto, H. Nann, S. A. Page, S. I. Penttilä, W. D. Ramsay, A. Salas-Bacci, S. Santra, M. Sharma, P. N. Seo, E. I. Sharapov, T. B. Smith, W. M. Snow, W. S. Wilburn, V. Yuan

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53 Scopus citations


The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry Aγ with respect to the neutron spin direction of γ rays emitted in the reaction n+p→d+γ using the capture of polarized cold neutrons on the protons in a liquid parahydrogen target. One expects parity-odd effects in the hadronic weak interaction between nucleons to be induced by the weak interaction between quarks. Aγ in n-+p→d+γ is dominated by a ΔI=1, 3S1-3P1 parity-odd transition amplitude in the n-p system. The first phase of the measurement was completed at the Los Alamos Neutron Science Center spallation source (LANSCE), with the result A γ=[-1.2±2.1(stat.)±0.2(sys.)]×10 -7. We also report the first measurement of an upper limit for the parity-allowed left-right asymmetry in this reaction, with the result A γ,LR=[-1.8±1.9(stat.)±0.2(sys.)]×10 -7. In this paper we give a detailed report on the theoretical background, experimental setup, measurements, extraction of parity-odd and parity-allowed asymmetries, analysis of potential systematic effects, and LANSCE results. The asymmetry has an estimated size of 5×10-8 and the aim of the NPDGamma collaboration is to measure it to 1×10-8. The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory.

Original languageEnglish (US)
Article number015505
JournalPhysical Review C - Nuclear Physics
Issue number1
StatePublished - Jan 31 2011

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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