Charge Structure of the Neutron

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This research addresses a fundamental question regarding the nature ofthe charge structure of the neutron --- one of the basic building blocksof matter: What is the spatial distribution of the constituent quarkswithin the neutron, which has a net zero charge? This question wasaddressed in Jefferson Laboratory Experiment 93-038 by scatteringlongitudinally polarized electrons quasielastically from a neutron indeuterium. Deuterium consists of a neutron and a proton bound looselytogether; it represents the best neutron target available. In acollision with the neutron, the electron transfers polarization to theneutron. Both components of the neutron polarization vector lie in thescattering plane: The transverse (or sideways) component is normal tothe momentum of the neutron, and the longitudinal component is parallel(or antiparallel) to the neutron momentum. By measuring both thesideways and the longitudinal polarizations, it is possible to extract aquantity called the neutron electric form factor, which is designated bythe letters GEN. Measurements of GEN as a function of momentum transferare related to the spatial distribution of charge within the neutron.The uncertainty in our knowledge of the interior charge density of theneutron becomes smaller as measurements of GEN are extended to highermomentum transfer. Knowledge of GEN is essential to understanding thestructure of matter. GEN is a fundamental quantity needed to challengemodels of nucleon structure, to make detailed microscopic calculationsof electric structure functions, and to interpret the results ofparity-violating experiments. The current research involves carryingout and completing a detailed analysis of the data obtained fromE93-038, preparing the results for publication, and preparing andcarrying out a new experiment to extract GEN at still higher momentumtransfers.