Excitation ofT=1Particle-Hole States inC12by Inelastic Electron Scattering

Abstract

The $T=1\mathrm{}$ single-particle-hole states of ${\mathrm{C}}^{12}$ are considered on the basis of the harmonic-oscillator shell model in the particle-hole formalism developed by Lewis and Walecka. Configuration mixing is included via a Serber-Yukawa residual interaction. Resulting mixed states lying close in energy are grouped together into complexes whose inelastic-electron-scattering form factors are then compared with recent experimental data. This comparison is done mainly at large momentum transfers and large scattering angles, where the transverse excitations (and consequently the $T=1\mathrm{}$ states) dominate, and where the excitation spectrum contains only a few strongly excited features (to be related here to collective single-particle-hole states). By working at high momentum transfer, the contributions from transitions of high multipolarity can be strongly enhanced. Here all possible $T=1\mathrm{}$ single-particle-hole states of all allowed angular momenta are considered in a basis including single-particle states up to the $2s-1d$ shell. A simple square-well shell model is used to account for the quasielastic cross section in the giant-resonance region. All of the gross features of the experimental excitation spectrum for excitation energies between 14 and 30 MeV can be accounted for on the basis of this simple model.