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Title: Meson exchange currents in neutron-proton bremsstrahlung

Abstract

Background: The meson exchange current (MEC) contribution is important in the neutron-proton bremsstrahlung process (np{gamma}) when the two nucleon-scattering angles are small. However, our understanding of such effects is limited, and the reason why meson exchange current effects dominate the np{gamma} cross section has not been thoroughly investigated. Purpose: The primary focus of this investigation is to understand the origin of the MEC contribution, to identify the leading MEC amplitudes, and to comprehend why these MEC amplitudes dominate the np{gamma} cross sections. Method: We used a new method that combines the one-boson-exchange (OBE) approach with the soft-photon approach to define 10 different np{gamma} amplitudes. These amplitudes are used to calculate np{gamma} cross sections at 225 MeV for nucleon laboratory scattering angles lying between 12 deg. and 43 deg. The results of these calculations are then compared to investigate the meson exchange current effect in np{gamma}. Results: (i) The OBE amplitude M{sub np{gamma}}{sub ,{mu}}{sup PS} and the two-u-two-t special (TuTts) soft-photon amplitude M{sub np{gamma}}{sub ,{mu}}{sup TuTts} predict quantitatively similar np{gamma} cross sections. (ii) The MEC effect is found to be significant when the two nucleon-scattering angles are far from the elastic limit (45 deg.), but the effect is insignificant when themore » nucleon angles approach the elastic limit. (iii) The origin of the MEC effect and the leading MEC amplitudes have been identified in this investigation. Furthermore, the reason is now clear why the leading MEC amplitudes dominate the np{gamma} cross section when the nucleon-scattering angles are small. (iv) The contribution from the anomalous magnetic moments of the proton and the neutron is confirmed to be negligibly small. (v) In general, the theoretical cross sections using the amplitude M{sub np{gamma}}{sub ,{mu}}{sup PS}, or the amplitude M{sub np{gamma}}{sub ,{mu}}{sup TuTts}, are consistent with the triple differential cross sections recently measured at the Los Alamos National Laboratory. However, there exists an unexplained discrepancy between theory and experiment in some cases. Conclusions: The findings of this investigation have enhanced our understanding of the meson exchange current effect in np{gamma}. The comparative amplitude method introduced can be used for other bremsstrahlung investigations.« less

Authors:
; ; ; ;  [1]
  1. College of Physics and Technology, Guangxi University, Nanning, Guangxi 530004 (China)
Publication Date:
OSTI Identifier:
21189891
Resource Type:
Journal Article
Journal Name:
Physical Review. C, Nuclear Physics
Additional Journal Information:
Journal Volume: 77; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevC.77.044001; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0556-2813
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; AMPLITUDES; BOSON-EXCHANGE MODELS; BREMSSTRAHLUNG; CURRENTS; DIFFERENTIAL CROSS SECTIONS; LANL; MAGNETIC MOMENTS; MEV RANGE; NEUTRONS; PHOTONS; PROTONS; SCATTERING

Citation Formats

Yi, Li, Liou, M K, Schreiber, W M, Gibson, B F, Timmermans, R G. E., Department of Physics and Institute for Nuclear Theory, Brooklyn College of the City University of New York, Brooklyn, New York 11210, Department of Physics, College of Staten Island of the City University of New York, Staten Island, New York 10314, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and Theory Group, Kernfysisch Versneller Instituut, University of Groningen Zernikelaan 25, NL-9747 AA Groningen. Meson exchange currents in neutron-proton bremsstrahlung. United States: N. p., 2008. Web. doi:10.1103/PHYSREVC.77.044001.
Yi, Li, Liou, M K, Schreiber, W M, Gibson, B F, Timmermans, R G. E., Department of Physics and Institute for Nuclear Theory, Brooklyn College of the City University of New York, Brooklyn, New York 11210, Department of Physics, College of Staten Island of the City University of New York, Staten Island, New York 10314, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, & Theory Group, Kernfysisch Versneller Instituut, University of Groningen Zernikelaan 25, NL-9747 AA Groningen. Meson exchange currents in neutron-proton bremsstrahlung. United States. https://doi.org/10.1103/PHYSREVC.77.044001
Yi, Li, Liou, M K, Schreiber, W M, Gibson, B F, Timmermans, R G. E., Department of Physics and Institute for Nuclear Theory, Brooklyn College of the City University of New York, Brooklyn, New York 11210, Department of Physics, College of Staten Island of the City University of New York, Staten Island, New York 10314, Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and Theory Group, Kernfysisch Versneller Instituut, University of Groningen Zernikelaan 25, NL-9747 AA Groningen. 2008. "Meson exchange currents in neutron-proton bremsstrahlung". United States. https://doi.org/10.1103/PHYSREVC.77.044001.
@article{osti_21189891,
title = {Meson exchange currents in neutron-proton bremsstrahlung},
author = {Yi, Li and Liou, M K and Schreiber, W M and Gibson, B F and Timmermans, R G. E. and Department of Physics and Institute for Nuclear Theory, Brooklyn College of the City University of New York, Brooklyn, New York 11210 and Department of Physics, College of Staten Island of the City University of New York, Staten Island, New York 10314 and Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 and Theory Group, Kernfysisch Versneller Instituut, University of Groningen Zernikelaan 25, NL-9747 AA Groningen},
abstractNote = {Background: The meson exchange current (MEC) contribution is important in the neutron-proton bremsstrahlung process (np{gamma}) when the two nucleon-scattering angles are small. However, our understanding of such effects is limited, and the reason why meson exchange current effects dominate the np{gamma} cross section has not been thoroughly investigated. Purpose: The primary focus of this investigation is to understand the origin of the MEC contribution, to identify the leading MEC amplitudes, and to comprehend why these MEC amplitudes dominate the np{gamma} cross sections. Method: We used a new method that combines the one-boson-exchange (OBE) approach with the soft-photon approach to define 10 different np{gamma} amplitudes. These amplitudes are used to calculate np{gamma} cross sections at 225 MeV for nucleon laboratory scattering angles lying between 12 deg. and 43 deg. The results of these calculations are then compared to investigate the meson exchange current effect in np{gamma}. Results: (i) The OBE amplitude M{sub np{gamma}}{sub ,{mu}}{sup PS} and the two-u-two-t special (TuTts) soft-photon amplitude M{sub np{gamma}}{sub ,{mu}}{sup TuTts} predict quantitatively similar np{gamma} cross sections. (ii) The MEC effect is found to be significant when the two nucleon-scattering angles are far from the elastic limit (45 deg.), but the effect is insignificant when the nucleon angles approach the elastic limit. (iii) The origin of the MEC effect and the leading MEC amplitudes have been identified in this investigation. Furthermore, the reason is now clear why the leading MEC amplitudes dominate the np{gamma} cross section when the nucleon-scattering angles are small. (iv) The contribution from the anomalous magnetic moments of the proton and the neutron is confirmed to be negligibly small. (v) In general, the theoretical cross sections using the amplitude M{sub np{gamma}}{sub ,{mu}}{sup PS}, or the amplitude M{sub np{gamma}}{sub ,{mu}}{sup TuTts}, are consistent with the triple differential cross sections recently measured at the Los Alamos National Laboratory. However, there exists an unexplained discrepancy between theory and experiment in some cases. Conclusions: The findings of this investigation have enhanced our understanding of the meson exchange current effect in np{gamma}. The comparative amplitude method introduced can be used for other bremsstrahlung investigations.},
doi = {10.1103/PHYSREVC.77.044001},
url = {https://www.osti.gov/biblio/21189891}, journal = {Physical Review. C, Nuclear Physics},
issn = {0556-2813},
number = 4,
volume = 77,
place = {United States},
year = {Tue Apr 15 00:00:00 EDT 2008},
month = {Tue Apr 15 00:00:00 EDT 2008}
}