  The nucleon self-energies of $^{40}$Ca and $^{48}$Ca are determined using a
nonlocal dispersive optical model (DOM). By enforcing the dispersion relation
connecting the real and imaginary part of the self-energy, scattering and
structure data are used to constrain these self-energies. The ability to
calculate both bound and scattering states simultaneously puts these
self-energies in a unique position to consistently describe exclusive knockout
reactions such as $(e,e'p)$. The present analysis reveals the importance of
high-energy proton reaction cross-section data in constraining spectroscopic
factors required for the description of the $(e,e'p)$ cross sections. In
particular, it is imperative that high-energy proton reaction cross-section
data are measured for $^{48}$Ca in the near future so that the quenching of the
spectroscopic factors in the $^{48}$Ca$(e,e'p)^{47}$K reaction can be
unambiguously constrained using the DOM. Measurements of proton reaction cross
sections in inverse kinematics employing rare isotope beams with large neutron
excess will provide corresponding constraints on proton spectroscopic factors
for exotic nuclei. Moreover, DOM generated spectral functions indicate that the
quenching of spectroscopic factors compared to $^{40}$Ca is not only due to
long-range correlation, but also partly due to the increase in high-momentum
protons in $^{48}$Ca on account of the strong neutron-proton interaction.
Single-particle momentum distributions of protons and neutrons in $^{48}$Ca
calculated from these spectral functions confirm that neutron excess causes a
higher fraction of high-momentum protons than neutrons.
