Nucleon-nucleon bremsstrahlung calculation: Studies of the off-shell proton electromagnetic vertex and of pseudoscalar vs pseudovector pion-nucleon couplings.
Item
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Title
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Nucleon-nucleon bremsstrahlung calculation: Studies of the off-shell proton electromagnetic vertex and of pseudoscalar vs pseudovector pion-nucleon couplings.
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Identifier
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AAI9908342
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identifier
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9908342
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Creator
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Li, Yi.
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Contributor
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Adviser: Ming Kung Liou
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Date
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1998
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Nuclear
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Abstract
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The nucleon-nucleon bremsstrahlung processes (pp{dollar}\gamma{dollar} and np{dollar}\gamma){dollar} have been used as a tool to study the problems related to both the off-shell proton electromagnetic vertex and pseudoscalar (ps) vs pseudovector (pv) {dollar}\pi{dollar}N coupling. We have developed an approach which can be applied to investigate the two problems together. The following important results have been obtained: (i) The pp{dollar}\gamma{dollar} analyzing powers calculated using the on-shell p{dollar}\gamma{dollar}p vertex, with ps or pv coupling, yield very poor results for most of the cases with small proton scattering angles at 280 MeV. (ii) The calculations using the off-shell p{dollar}\gamma{dollar}p vertex and ps coupling in most cases produce pp{dollar}\gamma{dollar} cross sections which fail to fit the TRIUMF data at 200 and 280 MeV. (iii) The pp{dollar}\gamma{dollar} data for both cross sections and analyzing powers in the energy region between 157 and 280 MeV can only be consistently described by the calculations using the off-shell p{dollar}\gamma{dollar}p vertex and pv coupling. Thus our results indicate that the off-shell p{dollar}\gamma{dollar}p vertex must be used in relativistic pp{dollar}\gamma{dollar} calculations, and the pseudovector coupling is the best choice for the {dollar}\pi{dollar}N vertex. (iv) The on-shell nucleon electromagnetic vertex has been applied to calculate np{dollar}\gamma{dollar} cross sections. The cross sections calculated using the ps coupling are extremely close to that calculated using the pv coupling, implying that the np{dollar}\gamma{dollar} results are not sensitive to the ps-pv question. (v) Exchange effects (the internal contribution) dominate the np{dollar}\gamma{dollar} cross section. This important fact is exactly what has been found in potential-model calculations. (vi) Noncoplanarity effects are very significant in both pp{dollar}\gamma{dollar} and np{dollar}\gamma{dollar} processes, even though such effects are quite different in the two processes. Noncoplanarity effects may be responsible for some discrepancies between theory and experiment. (vii) More accurate pp{dollar}\gamma{dollar} and np{dollar}\gamma{dollar} data, both cross sections and analyzing powers, are needed for further investigation of the off-shell nucleon electromagnetic vertex and of ps vs pv {dollar}\pi{dollar}N couplings.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
