Charge Structure of the Neutron

Kent State University, Kent OH

Investigators

Abstract

This research addresses a fundamental question regarding the nature of the charge structure of the neutron --- one of the basic building blocks of matter: What is the spatial distribution of the constituent quarks within the neutron, which has a net zero charge? This question was addressed in Jefferson Laboratory Experiment 93-038 by scattering longitudinally polarized electrons quasielastically from a neutron in deuterium. Deuterium consists of a neutron and a proton bound loosely together; it represents the best neutron target available. In a collision with the neutron, the electron transfers polarization to the neutron. Both components of the neutron polarization vector lie in the scattering plane: The transverse (or sideways) component is normal to the momentum of the neutron, and the longitudinal component is parallel (or antiparallel) to the neutron momentum. By measuring both the sideways and the longitudinal polarizations, it is possible to extract a quantity called the neutron electric form factor, which is designated by the letters GEN. Measurements of GEN as a function of momentum transfer are related to the spatial distribution of charge within the neutron. The uncertainty in our knowledge of the interior charge density of the neutron becomes smaller as measurements of GEN are extended to higher momentum transfer. Knowledge of GEN is essential to understanding the structure of matter. GEN is a fundamental quantity needed to challenge models of nucleon structure, to make detailed microscopic calculations of electric structure functions, and to interpret the results of parity-violating experiments. The current research involves carrying out and completing a detailed analysis of the data obtained from E93-038, preparing the results for publication, and preparing and carrying out a new experiment to extract GEN at still higher momentum transfers.