Coincidence 58Ni(e, e′pi) cross sections at moderate energy and momentum transfer

We present results of self-consistent Hartree-Fock (HF) and continuum random-phase-approximation (RPA) calculations for proton emission following the electro-excitation of 58Ni in the energy range ω = 25–42 MeV. The calculations are performed for four different values of the momentum transfer ranging between 0.4 and 0.8 fm⁻¹. For the above kinematics, an extensive amount of data is available. We confront the data with the theoretical results obtained within the plane-wave impulse approximation (PWIA), HF and RPA. The role of the final-state interaction (FSI) is investigated. Furthermore, we investigate in how far the angular distributions may reflect the occurrence of giant resonances. A quasi-free knockout (QFK) reaction picture is found unable to account for details of the data. Although the RPA offers a reasonable description of the overall q and ω behaviour of the angular distributions, it does not provide a good description of the proton-decay branch of the quadrupole and octupole resonance.