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

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PhysRevC.83.015505· OSTI ID:1007993

Gericke, M T; 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, G 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; Yuan, V

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 Aγ=[-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 Aγ,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.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1007993
• Report Number(s): JLAB-THY-11-1310; DOE/OR/23177-1478
• Journal Information: Physical Review. C, Nuclear Physics, Journal Name: Physical Review. C, Nuclear Physics Journal Issue: 1 Vol. 83; ISSN 0556-2813; ISSN PRVCAN
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ASYMMETRY
COLD NEUTRONS
LOS ALAMOS
NEUTRON SOURCES
NEUTRONS
NUCLEONS
ORNL
PARITY
PROTONS
QUARKS
SPALLATION
SPIN
TRANSITION AMPLITUDES
WEAK INTERACTIONS