Theoretical Study of Few-Body Processes

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Collision physics is entering an incredibly exciting time as a result of recent new experimental advances. One of these advances is the COLTRIMS (cold-target recoil-ion momentum spectroscopy) method. With this method, one can obtain full three-dimensional absolute cross sections for ionization of atoms and molecules by an arbitrarily charged particle. The most detailed information is contained in the fully differential cross section (FDCS) measurements in which the energy and angular location of all the final state particles are measured. Prior to COLTRIMS, FDCS measurements were made only for electron impact, normally only in the scattering plane, and the data were typically not absolute. With COLTRIMS, FDCS measurements are possible for any particle, any anti-particle, or arbitrarily charged ion. Now that these data are available to be compared with theory, there are surprises; the best theories are not in agreement with the experimental data.This research will investigate these open theoretical questions using a variety of different theoretical approaches ranging from first-order perturbation theory using the most accurate possible initial- and final state wavefunctions, to second-order distorted-wave approaches, to many-body perturbation theory. It is anticipated that different approaches will provide different insights into the physics of the collisions.