Parity Violation in Neutron-Proton Capture -- The NPD Gamma Experiment

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

DOI:https://doi.org/10.1016/j.nima.2009.07.057· OSTI ID:979115

Gericke, M. T. ^[1]; Bowman, James D ^[2]; Greene, G. L. ^[3]; Penttila, Seppo I ^[2]

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1. University of Manitoba, Canada
2. ORNL
3. University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL)

The NPDGamma collaboration has recently completed the first phase of a measurement to determine the size of the weak nucleon-nucleon interaction from cold neutron capture on a liquid hydrogen target. In the framework of the nearly 30 year old DDH model [B. Desplanques, J.F. Donoghue, B.R. Holstein, Annals of Physics 124 (1980) 449], the measured process is explained in terms of the weak pion-nucleon coupling, while the framework of modern effective field theory parameterizes the measured process in terms of the {sup 3}S{sub 1}-{sup 3}P{sub 1}, long range transition (essentially the Danilov parameter {rho}{sub t}) [S.L. Zhu et al., Nuclear Physics A 748 (2005) 435; C.-P. Liu, Phys. Rev. C 75 (2007) 065501]. The couplings in terms of either model are directly proportional to the parity violating up-down asymmetry in the angular distribution of gamma rays with respect to the neutron spin direction in the reaction {rvec n} + p {yields} d + {gamma}. The asymmetry has a predicted size of 5 x 10{sup -8} and the aim of the NPDGamma collaboration is to measure it to 20%. The first phase of the measurement was completed at the Los Alamos National Laboratory Neutron Science Center Spallation Source with a preliminary result of (-1.1 {+-} 2.1 stat. {+-} 0.2 sys.) x 10{sup -7}. Here, we report on the measurements and the results obtained so far. The experiment is currently being installed at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, for the remainder of its run time.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 979115
• Journal Information: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Journal Name: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Journal Issue: 2-3 Vol. 611
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
ANGULAR DISTRIBUTION
ASYMMETRY
COLD NEUTRONS
HYDROGEN
LANL
NEUTRON SOURCES
NEUTRONS
NUCLEAR PHYSICS
ORNL
PARITY
PHYSICS
SPALLATION
SPIN