Electroexcitation of isoscalar states in<i>sup16</i>O

Abstract

We report high resolution measurements of inelastic electron scattering to all narrow normal-parity states of $^{16}\mathrm{O}$ up to 12.05 MeV, which include states with ${J}_{n}^{\ensuremath{\pi}}$(${E}_{x}$ MeV): ${0}_{2}^{+}$(6.049), ${0}_{3}^{+}$(12.049), ${1}_{1}^{\mathrm{\ensuremath{-}}}$(7.117), ${2}_{1}^{+}$(6.917), ${2}_{2}^{+}$(9.845), ${2}_{3}^{+}$(11.52), ${3}_{1}^{\mathrm{\ensuremath{-}}}$(6.130), ${4}_{1}^{+}$(10.356), and ${4}_{2}^{+}$(11.097). The measurements were performed primarily at 90\ifmmode^\circ\else\textdegree\fi{} and 160\ifmmode^\circ\else\textdegree\fi{} and span momentum transfers between 0.6 and 2.6 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. Improved line shape fitting techniques have been developed. These are the first electron scattering measurements for the ${4}_{2}^{+}$ state and of second form-factor maxima for several states. The form factor for excitation of the ${2}_{2}^{+}$ state is strikingly different from that of the other ${2}^{+}$ states and indicates a transition density peaked in the interior. Transition charge densities were extracted from a combined data set that includes earlier electron scattering data renormalized to a recent analysis of elastic scattering from $^{16}\mathrm{O}$. Comparisons have been made with several structure models, including the Brown-Green model, the weak-coupling model, a 2\ensuremath{\Elzxh}\ensuremath{\omega} shell model, and the tetrahedral alpha-cluster model.