Structure of He

Only in the simplest approximation does the spin of He result entirely from the neutron. In actuality, small components of the wavefunction (D- and S-states) lead to non-zero proton polarizations. Spin asymmetries should be powerful tools for investigating the detailed structure of the ground state. A recent MIT/Bates experiment [Ha95] determined the asymmetry and carefully analyzed the model dependence related to NN potentials, nucleon form factors and off-shell prescriptions. It was concluded that, while, these uncertainties prevent an unambiguous determination of , the current theory is able to describe the energy transfer dependence of the asymmetry reasonably well as can be seen in Figure . Note that some 75%of the observed asymmetry is, in PWIA, due to proton polarization via the small wavefunction components. Full exploitation of spin-dependent electron scattering from He is an important component of future few-body physics.