Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Physics

Advisor's Name

Misak M. Sargsian

Advisor's Title

Committee Chair

Advisor's Name

Julian Edward

Advisor's Name

Rudolf Fiebig

Advisor's Name

Rajamani Narayanan

Keywords

Nuclear QCD, Hadronic Structure, Exclusive Reactions, Diquark Model, Photonuclear Reactions, Delta-Isobar Production

Date of Defense

5-25-2011

Abstract

The research presented in this dissertation investigated selected processes that involve baryons and nuclei in hard scattering reactions. These processes are characterized by the production of particles with large energies and transverse momenta. Through these processes, this work explored both, the constituent (quark) structure of baryons (specifically nucleons and ∆-Isobars), and the mechanisms through which the interactions between these constituents ultimately control the selected reactions.

The first of such reactions is the hard nucleon-nucleon elastic scattering, which was studied here considering the quark exchange between the nucleons to be the dominant mechanism of interaction in the constituent picture. In particular, it was found that an angular asymmetry exhibited by proton-neutron elastic scattering data is explained within this framework if a quark-diquark picture dominates the nucleon’s structure instead of a more traditional SU(6) three quarks representation. The latter yields an asymmetry around 90o center of mass scattering with a sign opposite to what is experimentally observed.

The second process is the hard breakup by a photon of a nucleon-nucleon system in light nuclei. Proton-proton (pp) and proton-neutron (pn) breakup in 3He, and ∆∆-isobars production in deuteron breakup were analyzed in the hard rescattering model (HRM), which in conjunction with the quark interchange mechanism provides a QCD description of the reaction. Through the HRM, cross sections for both channels in 3He photodisintegration were computed without the need of a fitting parameter. The results presented here for pp breakup show excellent agreement with recent experimental data.

In ∆∆-isobars production in deuteron breakup, the HRM angular distributions for the two ∆∆ channels were compared to the pn channel and to each other. An important prediction from this study is that the ∆++- channel consistently dominates ∆+0, which is in contrast with models that unlike the HRM consider a ∆∆ system in the initial state of the interaction. For such models both channels should have the same strength. These results are important in developing a QCD description of the atomic nucleus.

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