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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
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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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