Date of Completion

4-26-2019

Embargo Period

4-26-2019

Keywords

nuclear, physics, meson, deeply, virtual, electron, scattering, pseudoscalar, scalar, spin-0, spin, zero, kinematic, fitting, kinematic fitting, beam spin asymmetry, exclusivity

Major Advisor

Kyungseon Joo

Associate Advisor

Kawtar Hafidi

Associate Advisor

Peter Schweitzer

Field of Study

Physics

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

To understand the partonic structure of nucleons in nuclei, measuring the beam spin asymmetry (BSA) from exclusive processes is important to get at the so-called Generalized Parton Distributions (GPDs) that describe the partons’ behavior inside the nucleon. In particular, BSA in Deeply Virtual Meson Production (DVMP) can offer valuable constraints on the transverse GPDs which are not accessible with other exclusive processes. Furthermore, DVMP measurements on bound nucleons can offer insights into structure modification due to the nuclear environment.

The interpretation of this bounded nucleon DVMP on nuclear targets rests on the assumption of factorization and that higher-order effects are negligible. These assumptions can be tested through measurement of nuclear DVMP on a spin-0 target, where at leading order the BSA should be zero.

In the CLAS EG6 experiment, the spin-0 helium-4 gas target is probed via the deeply virtual (Q^2 > 2 (GeV/c)^2) photons from 6 GeV longitudinally polarized electrons. The results of coherent meson electroproduction of pi-zero off heliium-4, where the BSA is measured to be consistent with zero, will be presented and discussed. This benchmark measurement is in agreement with symmetry arguments of a recent theoretical formulation that offers a framework complementary to that of the GPDs and gives confidence in the assumptions made for future studies of exclusive nuclear processes.

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