Selectivity of the16O(e,e′pp)reaction to discrete final states

Abstract

Resolution of discrete final states in the16 O(e,e ′ pp) 14 C reaction may provide an interesting tool to discriminate between contributions from one-and two-body currents in this reaction. This is based on the observation that the 0 + ground state and first 2 + state of 14 C are reached predominantly by the removal of a 1 S0 pair from 16 O in this reaction, whereas other states mostly arise by the removal of a 3 P pair. This theoretical prediction has been supported recently by an analysis of the pair momentum distribution of the experimental data [1]. In this paper we present results of reaction calculations performed in a direct knock-out framework where final-state interaction and one-and two-body currents are included. The two-nucleon overlap integrals are obtained from a calculation of the two-proton spectral function of 16 O and include both long-range and short-range correlations. The kinematics chosen in the calculations is relevant for recent experiments at NIKHEF and Mainz. We find that the knock-out of a 3 P proton pair is largely due to the (two-body) ∆-current. The 1 S0 pair knock-out, on the other hand, is dominated by contributions from the one-body current and therefore sensitive to two-body short-range correlations. This opens up good perspectives for the study of these correlations in the 16 O(e,e ′ pp) reaction involving the lowest few states in 14 C. In particular the longitudinal structure function f00, which might be separated with super-parallel kinematics, turns out to be quite sensitive to the NN potential that is adopted in the calculations.

Self-consistent Green's function method for nuclei and nuclear matter

“…Figure 51 compares the cross sections for the calulations of Ref. [241,243] with the experimental data, as a function of the missing momentum at the three values of ω [244]. For this calculation final state interactions for the outgoing protons were taken into account by using distorted waves but neglecting their mutual interaction.…”

“…In the following we outline the approach taken in Refs. [245,241] and show a few results for the 16 O(e, e ′ pp) cross section. The sp spectral function of 16 O obtained in Ref.…”

“…Theoretically, these cross sections can be computed with the models developed by the Pavia [241,242] and Ghent [243] groups for the emission of both two protons or a proton-neutron pair. Calculation for the 16 O(e, e ′ pp) case have shown that the transition to the ground state of 14 C is dominated by the high-momentum components in the two-nucleon overlap function.…”

Nucleon-nucleon correlations and two-nucleon currents in exclusive(e,e′NN)reactions

“…In particular, it is impossible to take advantage of the fact that reactions leading to specific final states of the residual nucleus can be selective for one of the two-nucleon knockout mechanisms discussed above. Such a feature has been observed in theoretical studies of (e, e pp) an (e, e pn) reactions on 16 O [13,14]. On the other hand, however, a study of nuclear matter shall exhibit general features which are independent on the specific target nucleus considered and the corresponding long-range or low-energy correlations.…”

Final-state interactions in two-nucleon knockout reactions

“…In the 1990s, high-resolution A(e, e pp) measurements carried out at MAMI [8,9] and NIKHEF [10][11][12] could determine the transition to a specific final state of the residual A − 2 nucleus. When comparing to data for the 16 O(e, e pp) transition to the 0 + ground state of 14 C, model calculations [13][14][15] showed the clear dominance of SRC contributions to the cross section at low c.m. pair momentum, where the initial pair is in a relative S-state.…”