Abstract
The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry with respect to the neutron spin direction of rays emitted in the reaction 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. in is dominated by a , - 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 . We also report the first measurement of an upper limit for the parity-allowed left-right asymmetry in this reaction, with the result . 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 and the aim of the NPDGamma collaboration is to measure it to . The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory.
1 More- Received 1 March 2010
DOI:https://doi.org/10.1103/PhysRevC.83.015505
© 2011 American Physical Society