Transition properties of low-lying states in $^{28}$Si probed via inelastic proton and alpha scattering

Abstract

$0^+$, $1^-$, $2^+$, and $3^-$ excitations of $^{28}\textrm{Si}$ are investigated via proton and $α$ inelastic scattering off $^{28}\textrm{Si}$. The structure calculation of $^{28}\textrm{Si}$ is performed with the energy variation after total angular momentum and parity projections in the framework of antisymmetrized molecular dynamics (AMD). As a result of the AMD calculation, the oblate ground and prolate bands, $0^+$ and $3^-$ excitations, and the $1^-$ and $3^-$ states of the $K^π=0^-$ band are obtained. Using the matter and transition densities of $^{28}\textrm{Si}$ obtained by AMD, microscopic coupled-channel calculations of proton and $α$ scattering off $^{28}\textrm{Si}$ are performed. The proton-$^{28}\textrm{Si}$ potentials in the reaction calculation are microscopically derived by folding the Melbourne $g$-matrix $NN$ interaction with the AMD densities of $^{28}\textrm{Si}$. The $α$-$^{28}\textrm{Si}$ potentials are obtained by folding the nucleon-$^{28}\textrm{Si}$ potentials with an $α$ density. The calculation reasonably reproduces the observed elastic and inelastic cross sections of proton and $α$ scattering. Transition properties are discussed by combining the reaction analysis of proton and $α$ scattering and structure features such as transition strengths and form factors. The isoscalar monopole and dipole transitions are focused.