RUI: Hadronic Structure and Interactions

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This research focuses on two areas: (i) the description of hadron properties in terms of their constituent quarks and gluons, and (ii) the production of strangeness and charm in antiproton-proton interactions. (i) A hybrid approach will be used to describe hadron properties in terms of both perturbative and non-perturbative processes. A statistical model will represent perturbative degrees of freedom, and a meson cloud model will represent the nonperturbative fluctuation of baryons into meson-baryon states. A study of the pion-nucleon form factor will reduce the model-dependence of pion cloud contributions to this and other hadron structure calculations. This project will address one of the outstanding challenges to theory posed by recent experiment, the momentum-dependence of light quark distributions in the proton sea, and determine the parton contributions to strangeness and spin in the proton. Predictions will be made for experiments running at Fermilab and planned at JPARC. (ii) The creation of antihyperon-hyperon pairs in antiproton-proton annihilations tests theoretical models for the description of strangeness and charm production. Quark model calculations and reaction matrix analyses of these reactions will be made and compared to meson-exchange and constituent quark models, and to recent spin transfer measurement results from CERN, which disagree with all theoretical calculations. Cross sections and spin observables will be calculated for the experiments planned by the PANDA collaboration at FAIR, which will extend the CERN measurements to higher energies and to the production of charmed hyperons. Nucleons (protons and neutrons) and other hadrons are particles composed of quarks, gluons, and a fluctuating sea of quark-antiquark pairs. In this research we study the fundamental questions of how the properties of a particle are determined by the properties of its constituents, and how those constituents affect the ways in which particles interact with one another. An example of this type of question is proton spin. The proton spin is 1/2, but it consists of many quarks (spin 1/2) and gluons (spin 1). How do all these spins add up to give us a spin-1/2 proton? This work will be carried out with undergraduate research assistants from Seattle University. Their research experience will provide an integration of classroom learning and the excitement of contemporary research. Students will receive training in research methods and scientific communication. They will work in teams, mentor younger students and present their work in papers, posters and talks at meetings of professional societies. They will also share their work with the local campus community in seminars and events sponsored by Seattle University student research organizations.