Spin Polarization in Electron Scattering off Few - Nuclei.
The purpose of this investigation is twofold: to establish a relativistic formalism for the description of inelastic, two-body, coincidence, electron scattering off few-body nuclei with spins one half or one, and to investigate the role of strangeness-induced weak-neutral -current matrix elements of few-body nuclei and parity-violating admixtures to the nucleon wave function in elastic, parity -violating electron-nucleus scattering. Helicity formalism was used in the formulation of comprehensive treatments of all single-polarization observables in scalar and pseudo-scalar electro-production off spin one half targets and all single- and double-polarization observables in deuteron two-body photo- and electro-disintegration, from a unified standpoint. A discussion of necessary and sufficient measurements needed for a complete determination of all transition amplitudes is given. Wigner rotation of the recoil polarization coincidence electro-disintegration and electro-production structure functions due to the boost from the centre-of-mass to the lab frame are calculated. Inequalities among polarized spin one half target and unpolarized ejectile as well as unpolarized target and polarized spin one half ejectile coincidence structure functions due to the positivity of the polarized coincidence cross section are derived for arbitrary reactions with spin one half targets and ejectiles. It is shown how to separate strangeness-induced form factors of the nucleon from elastic, parity-violating electron scattering data. A parity-violating quark-quark potential is derived by a non-relativistic reduction of one-W^+/-,Z^circ -exchange Feynman diagrams. The abnormal parity admixture in the nucleon wave function is calculated using first order perturbation theory in a non-relativistic quark model with harmonic oscillator wave functions and the lowest -lying negative parity nucleon resonances. The contribution of these parity admixtures to the elastic parity-violating electromagnetic current matrix element of the nucleon is evaluated. Special attention is paid to the gauge invariance of the calculation: gauge invariance preserving two-body quark parity-violating electromagnetic current is constructed. It is shown that the elastic parity-violating electromagnetic current matrix element has the correct behaviour in the long-wave-length limit only if all abnormal parity admixtures to the wave function are included. A new definition of the parity-violating, time-reversal preserving elastic electromagnetic current matrix element, which automatically satisfies the threshold theorem, is given. An exact argument, based on closure, about the contribution of all parity admixtures to the elastic parity-violating electromagnetic current matrix element is established. The complete elastic parity-violating electromagnetic current matrix element of the nucleon is shown to vanish identically, to first order in G_ F, in all non-relativistic quark models with spin and iso-spin independent, local, strong quark-quark potentials. ftn*Originally published in DAI, Vol. 52 No. 3. Reprinted here with corrected bibliographic information.
- Pub Date:
- January 1990
- Physics: Nuclear