Nuclear dynamics and quasi-elastic electron scattering

We present results of calculations of the longitudinal and transverse response function for inelastic electron scattering from 56Fe and 12C. In the impulse approximation it is found that the calculated longitudinal response is approximately forty percent too large for 56Fe. We discuss those aspects of nuclear dynamics which could account for this discrepancy and suggest that the depletion of the shell model orbitals through various (short-range) correlation effects may play an important role. It is suggested that a significant longitudinal response may exist at energies above the quasi-elastic domain; this response would involve the excitation of 2p-2h states. In our model there is a significant disagreement between theory and experiment for the transverse response. We ascribe this disagreement to meson-exchange-current effects; however, we present no calculations of such effects in this work. Recent work on meson-exchange-current contributions to the transverse response, based upon a Fermi-gas model, indicates enhancements of the required magnitude may be obtained from virtual excitations of the Δ isobar. Further quantitative studies of these effects in finite nuclei are required. If our model for the quenching of the longitudinal response in the quasi-elastic domain proves to be correct, we can infer that quasi-elastic electron scattering studies may provide a measurement of the average probability of the occupation of a shell model orbital. We conclude that if the impulse approximation is modified to include both the effect of the renormalization of the quasi-particle pole and the meson-exchange-current effects, one can explain the longitudinal and transverse response simultaneously