Abstract
We determine the Coulomb sum for 4He using the world data on 4He(e,e′) and compare the results to calculations based on realistic interactions and including two-body components in the nuclear charge operator. We find good agreement between theory and experiment when using free-nucleon form factors. The apparent reduction of the in-medium GEp implied by IA-interpretation of the L/T-ratios measured in 4He(e,e′p) and 4He(e→,e′p→) is not confirmed.
Highlights
The conjecture of a modification of the form factors of a nucleon embedded in the nuclear medium has received considerable attention during the last few years
This conjecture first arose in connection with measurements of the Coulomb sum rule (CSR) in nuclei like C, Ca and Fe [1,2]
These were found to be much too low relative to theoretical predictions based on the square of the free proton charge form factor GEp, to which the CSR is approximately proportional
Summary
The conjecture of a modification of the form factors of a nucleon embedded in the nuclear medium has received considerable attention during the last few years. This conjecture first arose in connection with measurements of the Coulomb sum rule (CSR) in nuclei like C, Ca and Fe [1,2] These were found to be much too low relative to theoretical predictions based on the square of the free proton charge form factor GEp, to which the CSR is approximately proportional. J. Carlson et al / Physics Letters B 553 (2003) 191–196 about a possible medium-modified ratio of the proton charge and magnetic form factors, GEp/GMp. Recently, polarization transfer experiments of the type (e, e p) [10,11] have measured ratios of asymmetries Px/Pz which, in plane-wave-impulse-approximation (PWIA), are proportional to GEp/GMp. After correcting the data for FSI effects—for caveats concerning meson exchange currents (MEC), see below— ratios smaller than those for free protons have been inferred. For this target the (e, e p) and (e, e p) experiments have found large deviations from the free GEp/GMp [7,8,9,10,11]
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