IN-MEDIUM BEHAVIOR OF VECTOR-MESONS AND THE LONGITUDINAL AND TRANSVERSE RESPONSE FUNCTIONS IN (E, E'P) REACTIONS

The electromagnetic form factors of nucleons appear dominated by vecto r mesons at momentum transfers smaller than approximately 1 GeV/c. It is therefore expected that measurements of quantities involving the el ectromagnetic form factors of nucleons embedded in nuclei will be sens itive to changes in vector-meson properties arising from their interac tion with the medium. Longitudinal and transverse response functions m easured in quasi-elastic (e, e'p) reactions provide such data for two very different operators, the charge and the current densities. We sho w that a decrease of vector-meson masses in the medium, consistent wit h present expectations about chiral-symmetry restoration in nuclei, pr oduces the quenching observed in the longitudinal response of light sy stems (He-3, He-4) and part of this quenching for heavier nuclei (Ca-4 0) where nuclear correlations are expected to generate an additional s uppression of the longitudinal response. The transverse response is al most unchanged, which is in agreement with the data. Difficulties in e xtracting very quantitative information on the in-medium behaviour of vector mesons from (e, e'p) data are pointed out.