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Measurement of parity violation in np capture: the NPDGamma experiment

Journal Article · · Journal of Research of the National Institute of Standards and Technology
DOI:https://doi.org/10.6028/jres.110.024· OSTI ID:2470433
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  1. Univ. of Manitoba, Winnipeg, MB (Canada)
  2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
  3. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
  4. Univ. of California, Berkeley, CA (United States)
  5. Univ. of Michigan, Ann Arbor, MI (United States)
  6. Univ. of New Hampshire, Durham, NH (United States)
  7. Univ. of Tennessee, Knoxville, TN (United States)
  8. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  9. KEK National Laboratory, Tsukuba (Japan)
  10. Hamilton College, Clinton, NY (United States)
  11. Indiana Univ., Bloomington, IN (United States)
  12. Joint Inst. for Nuclear Research (JINR), Dubna (Russian Federation)
  13. University of Dayton, OH (United States)
+ Show Author Affiliations
The NPDGamma experiment will measure the parity-violating directional gamma ray asymmetry Aγ in the reaction $$\vec{n}$$ + p → d + γ. Ultimately, this will constitute the first measurement in the neutron-proton system that is sensitive enough to challenge modern theories of nuclear parity violation, provid ing a theoretically clean determination of the weak pion-nucleon coupling. A new beam line at the Los Alamos Neutron Science Center (LANSCE ) delivers pulsed cold neutrons to the apparatus, where they are polarized by transmission through a large volume polarized 3 He spin filter and cap tured in a liquid para-hydrogen target. The 2.2 MeV gamma rays from the capture reac tion are detected in an array of CsI(Tl) scin tillators read out by vacuum photodiodes operated in current mode. We will complete commissioning of the apparatus and carry out a first measurement at LANSCE in 2004-05, which would provide a statistics limited result for Aγ accurate to a standard uncertainty of ±5 × 10–8 level or better, improving on existing measurements in the neutron-proton system by a factor of 4. Plans to move the experiment to a reactor facility, where the greater flux would enable us to make a measurement with a standard uncertainty of ±1 × 10–8, are actively being pursued for the longer term.
Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
89233218CNA000001
OSTI ID:
2470433
Journal Information:
Journal of Research of the National Institute of Standards and Technology, Journal Name: Journal of Research of the National Institute of Standards and Technology Journal Issue: 3 Vol. 110; ISSN 1044-677X
Publisher:
National Institute of Standards (NIST)Copyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
hadronic weak interaction
neutron capture
parity violation