Giant Resonances in the Doubly Magic Nucleus ${}_{}{}^{48}{}_{}{}^{}Ca$ from the ( $\mathit{e},{\mathit{e}}^{\prime }\mathit{n}$) Reaction

The ${}^{48}\mathrm{Ca}\left({e,e}^{\prime }n\right)$ reaction has been investigated for excitation energies 11–25 MeV and momentum transfers $0.22–0.43{\mathrm{fm}}^{-1\mathrm{}}$ at the superconducting Darmstadt electron linear accelerator S-DALINAC. Electric dipole and quadrupole plus monopole strength distributions are extracted from a multipole decomposition of the spectra. Their fragmented structure is described by microscopic calculations allowing for coupling of the basic particle-hole excitations to more complex configurations. Comparison of the excitation spectrum of the residual nucleus ${}^{47}\mathrm{Ca}$ with statistical model calculations reveals a $39\left(5\right)\%$ contribution of direct decay to the damping of the giant dipole resonance.