How well we know the structure of the proton depends on our knowledge of the form factors of the proton. The ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer methods differ by a factor of 3 at four momentum transfer squared (Q²)=5.6 GeV². The two photon exchange (TPE) effect is the leading candidate to explain this discrepancy. The theoretical estimates of the TPE effect are model dependent so precise measurement is required to resolve this problem. The TPE effect can be measured in a model independent way by measuring the ratio of positron-proton to electron-proton elastic scattering cross-sections. We produced a simultaneously mixed electron-positron beam in the engineering test run computed in October 2006 and measured the e +p/e− p ratio using the CEBAF large acceptance spectrometer (CLAS). Due to the luminosity constraint our kinematic coverage is limited to low Q² and high ϵ (longitudinal polarization of the virtual photon). We continued our background study through GEANT4 simulation developed for the test run design in order to find more background sources and to design required shielding. The simulation is validated by using the test run data and is used further to optimize the luminosity for the final experiment. We are able to increase the luminosity by an order of magnitude for the upcoming final run. The final experiment will extend the data in high Q² and low ϵ region where TPE effect is expected to be large.
","abstract_html":"<p>How well we know the structure of the proton depends on our knowledge of the form factors of the proton. The ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer methods differ by a factor of 3 at four momentum transfer squared (<em>Q</em>²)=5.6 GeV². The two photon exchange (TPE) effect is the leading candidate to explain this discrepancy. The theoretical estimates of the TPE effect are model dependent so precise measurement is required to resolve this problem. The TPE effect can be measured in a model independent way by measuring the ratio of positron-proton to electron-proton elastic scattering cross-sections. We produced a simultaneously mixed electron-positron beam in the engineering test run computed in October 2006 and measured the <em>e</em> +<em>p/e</em>− <em>p</em> ratio using the CEBAF large acceptance spectrometer (CLAS). Due to the luminosity constraint our kinematic coverage is limited to low <em>Q</em>² and high ϵ (longitudinal polarization of the virtual photon). We continued our background study through GEANT4 simulation developed for the test run design in order to find more background sources and to design required shielding. The simulation is validated by using the test run data and is used further to optimize the luminosity for the final experiment. We are able to increase the luminosity by an order of magnitude for the upcoming final run. The final experiment will extend the data in high <em>Q</em>² and low ϵ region where TPE effect is expected to be large.</p>","abstract_has_math":false,"creators":["Niroula, Megh Raj"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Lawrence B. Weinstein","Charles I. Sukenik","Gail E. Dodge","Hari Areti","Scott R. Sechrist"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2010,"date_issued":"2010-04-01T07:00:00Z","date_published":"2010-04-01T07:00:00Z","updated_at":"2026-07-24T03:34:18Z","subjects":["Born approximation","Elastic scattering","Two-photon exchange","Elementary Particles and Fields and String Theory","Nuclear"],"languages":[],"rights":["In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
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"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["9781124148083","https://digitalcommons.odu.edu/physics_etds/65"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["How well we know the structure of the proton depends on our knowledge of the form factors of the proton. The ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer methods differ by a factor of 3 at four momentum transfer squared (Q²)=5.6 GeV². The two photon exchange (TPE) effect is the leading candidate to explain this discrepancy. The theoretical estimates of the TPE effect are model dependent so precise measurement is required to resolve this problem. The TPE effect can be measured in a model independent way by measuring the ratio of positron-proton to electron-proton elastic scattering cross-sections. We produced a simultaneously mixed electron-positron beam in the engineering test run computed in October 2006 and measured the e +p/e− p ratio using the CEBAF large acceptance spectrometer (CLAS). Due to the luminosity constraint our kinematic coverage is limited to low Q² and high ϵ (longitudinal polarization of the virtual photon). We continued our background study through GEANT4 simulation developed for the test run design in order to find more background sources and to design required shielding. The simulation is validated by using the test run data and is used further to optimize the luminosity for the final experiment. We are able to increase the luminosity by an order of magnitude for the upcoming final run. The final experiment will extend the data in high Q² and low ϵ region where TPE effect is expected to be large.
"]},{"key":"dc:title","label":"Title","values":["Beyond the Born Approximation: A Precise Comparison of e+p and e-p Elastic Scattering in the CEBAF Large Acceptance Spectrometer (CLAS)"]}]}],"canonical_facts":{"dc:contributor":["Lawrence B. Weinstein","Charles I. Sukenik","Gail E. Dodge","Hari Areti","Scott R. Sechrist"],"dc:creator":["Niroula, Megh Raj"],"dc:date.available":["2019-02-21T08:00:00Z"],"dc:description.abstract":["How well we know the structure of the proton depends on our knowledge of the form factors of the proton. The ratio of the electromagnetic form factors of the proton measured by the Rosenbluth and the polarization transfer methods differ by a factor of 3 at four momentum transfer squared (Q²)=5.6 GeV². The two photon exchange (TPE) effect is the leading candidate to explain this discrepancy. The theoretical estimates of the TPE effect are model dependent so precise measurement is required to resolve this problem. The TPE effect can be measured in a model independent way by measuring the ratio of positron-proton to electron-proton elastic scattering cross-sections. We produced a simultaneously mixed electron-positron beam in the engineering test run computed in October 2006 and measured the e +p/e− p ratio using the CEBAF large acceptance spectrometer (CLAS). Due to the luminosity constraint our kinematic coverage is limited to low Q² and high ϵ (longitudinal polarization of the virtual photon). We continued our background study through GEANT4 simulation developed for the test run design in order to find more background sources and to design required shielding. The simulation is validated by using the test run data and is used further to optimize the luminosity for the final experiment. We are able to increase the luminosity by an order of magnitude for the upcoming final run. The final experiment will extend the data in high Q² and low ϵ region where TPE effect is expected to be large.
"],"dc:identifier":["9781124148083","https://digitalcommons.odu.edu/physics_etds/65"],"dc:rights":["In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).
"],"dc:subject":["Born approximation","Elastic scattering","Two-photon exchange","Elementary Particles and Fields and String Theory","Nuclear"],"dc:title":["Beyond the Born Approximation: A Precise Comparison of e+p and e-p Elastic Scattering in the CEBAF Large Acceptance Spectrometer (CLAS)"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T03:34:18Z"}