Title: Measurement of Parity-Violating y-ray Asymmetry in the Capture of Polarized Cold Neutrons on Protons

Abstract

The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry A{sub {gamma}} with respect to the neutron spin direction of {gamma} rays emitted in the reaction n + p {yields} 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{sub {gamma}} in n + p {yields} d + {gamma} is dominated by a {Delta}I = 1, {sup 3}S{sub 1-}{sup 3}P{sub 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{sub {gamma}} = [-1.2 {+-} 2.1 (stat.) {+-} 0.2 (sys.)] x 10{sup -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{sub {gamma}LR} = [-1.8 {+-} 1.9 (stat.) {+-} 0.2 (sys.)] x 10{sup -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, andmore » LANSCE results. The asymmetry has an estimated size of 5 x 10{sup -8} and the aim of the NPDGamma collaboration is to measure it to 1 x 10{sup -8}. The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory.« less

Authors:

Gericke, M T ^[1]; Bowman, James D ^[2]; Greene, Geoffrey L ^[2]; Penttila, Seppo ^[3]; NPD, Gamma ^[4]

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+ Show Author Affiliations

1. University of Manitoba, Canada
2. ORNL
3. Oak Ridge National Laboratory (ORNL)
4. Collaboration

Publication Date:

2011-01-01

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1004678

DOE Contract Number:  

DE-AC05-00OR22725

Resource Type:

Journal Article

Journal Name:

Physical Review C

Additional Journal Information:

Journal Volume: 83; Journal Issue: 1; Journal ID: ISSN 0556--2813

Country of Publication:

United States

Language:

English

Subject:

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