Type of Work
Physical Review C
The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry A(gamma) with respect to the neutron spin direction of gamma rays emitted in the reaction (n) over right arrow + p -> d + gamma 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. A(gamma) in (n) over right arrow + p -> d + gamma is dominated by a Delta I = 1, S-3(1)-P-3(1) 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(gamma) = [-1.2 +/- 2.1 (stat.) +/- 0.2 (sys.)] x 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(gamma,LR) = [-1.8 +/- 1.9 (stat.) +/- 0.2 (sys.)] x 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 x 10(-8) and the aim of the NPDGamma collaboration is to measure it to 1 x 10(-8). The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory.
Gericke, M. T.; Alacorn, R.; Balascuta, S.; Barron-Palos, L.; Blessinger, C.; Bowman, J. D.; Carlini, R. D.; Chen, W.; Chupp, T. E.; Crawford, C.; Covrig, S.; Dabaghyan, M.; Fomin, N.; Freedman, S. J.; Gentile, T. R.; Gillis, R. C.; Greene, G. L.; Hersman, F. W.; Ino, T.; Jones, Gordon L.; Lauss, B.; Leuschner, M.; Lozowski, W. R.; Mahurin, R.; Masuda, Y.; Mei, J.; Mitchell, G. S.; Muto, S.; Nann, H.; Page, S. A.; Penttila, S. I.; Ramsay, W. D.; Salas-Bacci, A.; Santra, S.; Sharma, M.; Seo, P.-N.; Sharapov, E. I.; Smith, T. B.; Snow, W. M.; Wilburn, W. S.; and Yuan, V., "Measurement of parity-violating gamma-ray asymmetry in the capture of polarized cold neutrons on protons" (2011). Hamilton Digital Commons.
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