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Link to publication Citation for published version (APA):Zondervan, A., de Bever, L. J., Jans, E., Konijn, J., Kruijer, M., Steijger, J. J. M., ... Vanderhaeghen, M. (1995). The 12C(e, ep) and 12C(e, epp) reactions in the -resonance region. Nuclear Physics A, 587(4), 697-720. DOI: 10.1016/0375-9474(95)00044-2 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The 12C(e, e' p) and 12C(e, e' pp) reactions in the A-resonance region AbstractCoincidence cross sections for the "C(e, e'pp) and "C(e, e'p) reactions have been measured in the A-resonance region. The '*C(e, e'pp) reaction has been measured at three different angular settings of the proton detectors to investigate the angular correlation between the emitted protons. The data, which have a low statistical accuracy, are compared with a calculation based on the direct-knockout mechanism, which includes one-and two-body currents. NN-correlations are accounted for via a correlation function, A-excitation via a two-body current and final-state interactions of the emitted protons via an optical potential. The "C(e, e'p) data, taken at large proton-emission angles, cover the region of high missing-energy values

The contributions from 12 C(e, e ′ pn) and 12 C(e, e ′ pp) to the semi-exclusive 12 C(e, e ′ p) cross section have been calculated in an unfactorized model for two-nucleon emission. We assume direct two-nucleon knockout after virtual photon coupling with the two-body pion-exchange currents in the target nucleus. Results are presented at several kinematical conditions in the dip and ∆(1232) regions. The calculated two-nucleon knockout strength is observed to account for a large fraction of the measured (e, e ′ p) strength above the two-nucleon emission threshold.

The reaction '*C(e,e'p)"B has been studied in the dip region at an energy transfer w = 212 MeV, a three-momentum transfer 141 = 270 MeV/c, and missing momenta in the range from 360 MeV/c to 600 MeV/c. Data have been obtained for the ground-state transition and a multiplet of states centered at an excitation energy of about 7 MeV in "B. Distorted-wave impulse approximation calculations under-estimate the data for the ground-state transition and those for the multiplet of states by one and two orders of magnitude, respectively. Long-range correlations in the initial state bring the results of the calculations closer to the data, while two-step processes are shown to increase the calculated strength for the excitation of the multiplet of states by an order ot magnitude relative to the one-step calculations. Calculations that include two-body currents are able to give a proper account of both data sets.Single-particle properties of nuclei have been studied in considerable detail with high-resolution (e, e'p) experiments in the quasi-elastic domain [ 1,2]. The measured proton spectroscopic factors were shown to be quenched by about 3040% compared to shellmodel values for a large range of transitions in various nuclei. These results have been interpreted in the framework of many-body theory [ 31 as evidence for short-and long-range correlations between nucleons in nuclei. In the same framework it is predicted that short-range correlations generate high-momentum components in the nucleon spectral function, which will be mainly manifest at large excitation energies [4,5]. Long-range correlations, on the other hand, are expected to cause a strong enhancement of highmomentum components at lower excitation energies [6,7]. In order to investigate these predictions of many-body theory (e, e'p) experiments at high missing momenta covering a large range of excitation energies are needed.Recently, the first experimental results on high proton momenta in complex nuclei, i.e. *'*Pb and 160, were published [ 8,9]. In both cases an enhancement of the proton momentum distributions for low-lying hole states in the momentum range beyond 300 MeV/c was observed. For *08Pb the results are well described by distorted-wave impulse approximation (DWIA) calculations that include the effects of long-range correlations [ 71 by using quasi-particle wave functions [ 81.The importance of such effects was not investigated 0370.2693/96/$12.00 0 1996 Eisevier Science B.V. All rights reserved SSDI 0370-2693(95)01314-8

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