Missing strength in longitudinal electron response and y-scaling

Abstract

We propose that some of the missing strength in the longitudinal electron response in nuclei results from changes in the electromagnetic form factor in medium. In the chiral bag model the virtual γ-ray couples partly through vector mesons, partly directly to quarks in the bag. In the low momentum region, where the former is important, if the vector meson mass decreases in medium as we argue then there will be a decrease in the form factor. Net effects from this are not large, however. At higher momenta q∼1 GeV/ c the form factor is dominated by the direct coupling to the quarks. This does not seem to change appreciably for densities up to nuclear matter density. Thus, experiments, such as y-scaling, which look chiefly at these higher momenta will not see much change in the nucleon properties.