The nuclear mass dependence of the number of short-range correlated (SRC) proton-proton (pp) and proton-neutron (pn) pairs in nuclei is a sensitive probe of the dynamics of short-range pairs in the ground state of atomic nuclei. This work presents an analysis of electroinduced single-proton and two-proton knockout measurements off 12 C, 27 Al, 56 Fe, and 208 Pb in kinematics dominated by scattering off SRC pairs. The nuclear mass dependence of the observed A(e, e pp)/ 12 C(e, e pp) cross-section ratios and the extracted number of pp-and pn-SRC pairs are much softer than the mass dependence of the total number of possible pairs. This is in agreement with a physical picture of SRC affecting predominantly nucleon-nucleon pairs in a nodeless relative-S state of the mean-field basis.
Background: Exclusive two-nucleon knockout after electroexcitation of nuclei (A(e, e N N ) in brief) is considered to be a primary source of information about short-range correlations (SRC) in nuclei. For a proper interpretation of the data, final-state interactions (FSI) need to be theoretically controlled.Purpose: Our goal is to quantify the role of FSI effects in exclusive A(e, e pN ) reactions for four target nuclei representative for the whole mass region. Our focus is on processes that are SRC driven. We investigate the role of FSI for two characteristic detector setups corresponding with a "small" and "large" coverage of the available phase space.Method: Use is made of a factorized expression for the A(e, e pN ) cross section that is proportional to the two-body center-of-mass (c.m.) momentum distribution of close-proximity pairs. The A(e, e pp) and A(e, e pn) reactions for the target nuclei 12 C, 27 Al, 56 Fe and 208 Pb are investigated. The elastic attenuation mechanisms in the FSI are included using the relativistic multiple-scattering Glauber approximation (RMSGA). Single-charge exchange (SCX) reactions are also included. We introduce the nuclear transparency T pN A , defined as the ratio of exclusive (e, e pN ) cross sections on nuclei to those on "free" nucleon pairs, as a measure for the aggregated Conclusion:The SCX mechanisms represent a relatively small (order of a few percent) contribution of SRCdriven A(e, e pN ) processes. The mass dependence of FSI effects in exclusive A(e, e pN ) can be captured in a robust power law and is in agreement with the predictions obtained in a toy model.
We investigate the factorization properties of the exclusive electroinduced two-nucleon knockout reaction A(e,e pN). A factorized expression for the cross section is derived and the conditions for factorization are studied. The A(e,e pN) cross section is shown to be proportional to the conditional center-of-mass (c.m.) momentum distribution for close-proximity pairs in a state with zero relative orbital momentum and zero radial quantum number. The width of this conditional c.m. momentum distribution is larger than the one corresponding with the full c.m. momentum distribution. It is shown that the final-state interactions (FSIs) only moderately affect the shape of the factorization function for the A(e,e pN) cross sections. Another prediction of the proposed factorization is that the mass dependence of the A(e,e pp) [A(e,e pn)] cross sections is much softer than[NZ].
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