Inelastic electron scattering to negative parity states ofSi28

Abstract

Negative-parity states of $^{28}\mathrm{Si}$ are studied by high-resolution inelastic electron scattering. The form factors of the ${1}^{\ensuremath{-}}$ (8.904), ${5}^{\ensuremath{-}}$ (9.702), ${1}^{\ensuremath{-}}$, ${2}^{\ensuremath{-}}$ (9.929), ${3}_{2}^{\ensuremath{-}}$ (10.180), and ${4}^{\ensuremath{-}}$ $T=1$ (12.664) states are determined for the first time, for momentum transfers between 0.9 and 2.4 ${\mathrm{fm}}^{\ensuremath{-}1}$. The ${3}_{1}^{\ensuremath{-}}$ (6.879) state is studied by subtracting off the theoretical contribution of the nearby ${4}^{+}$ (6.889) state. An upper limit for the ${5}^{\ensuremath{-}}$ $T=1$ (13.248) is established. The ${3}^{\ensuremath{-}}$ $T=\frac{0}{{6}^{\ensuremath{-}}}$ $T=0$ complex (11.58) remains unresolved. We present evidence for oblate-prolate deformation changes in the ${3}^{\ensuremath{-}}$ $T=0$ states. The experimental data are compared with predictions of the open-shell random phase approximation of Rowe and Wong. In $^{28}\mathrm{Si}$, the open-shell random phase approximation is demonstrated to be extremely sensitive to the ground state wave function used, and other possible limitations of the open-shell random phase approximation are discussed.NUCLEAR REACTIONS $^{28}\mathrm{Si}$ ($e, {e}^{\ensuremath{'}}$), $E=96\ensuremath{-}279$ MeV, $\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{}, 160\ifmmode^\circ\else\textdegree\fi{}$, negative parity states; measured $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}(E, \ensuremath{\theta})$; deduced electromagnetic form factors, Tassie model parameters, $B(\mathit{\ensuremath{\lambda}})$ values. Open-shell random phase approximation calculations.