Polarized Electron Scattering from Nucleons

College Of William And Mary, Williamsburg VA

Investigators

Abstract

This research grant supports a program of electromagnetic and weak current experiments to probe the flavor content and spin structure of protons and neutrons (nucleons). At present, these properties of the nucleon cannot be precisely predicted using quantum chromodynamics, the accepted fundamental theory of the strong interaction, and so experiment must lead the way. A series of parity-violating electron scattering experiments at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) will enable us to determine the strange quark "sea" contribution to the nucleon ground state. These experiments include a measurement in Hall A of the parity-violating asymmetry in scattering from the proton at low momentum transfer, and measurements of the asymmetry in scattering from 4He and 208Pb. The G0 parity-violation experiment in Hall C is moving from the design and construction stage to the commissioning and data-taking stage. This experiment will definitively map out the strange quark vector form factors for the nucleon as a function of momentum transfer. A measurement of the asymmetry for the N to Delta(1232) transition will be made simultaneously, and planned measurements on deuterium will probe the axial form factor. A new initiative is under development to use a modified version of the G0 spectrometer to perform a parity-violation electron scattering experiment at very low momentum transfer, in order to make a sensitive search for physics beyond the standard model. A series of polarized electron scattering experiments at Jefferson Lab are dedicated to elucidating the spin structure of the nucleon using polarized 3He targets. This program is well underway, three experiments using these targets will take place in the next year at Jefferson Lab, and a 3He target cell lab at William and Mary supports this program.