Evidence for the modification of nucleon properties in nuclei from traditional nuclear physics experiments

We consider the manifestation of the quark presence in nuclei. We discuss deep-inelastic electron scattering at both high and low momentum transfer, and also discuss, at some length, elastic electron-nucleus scattering. Recent experiments have led to the conclusion that the quark distribution in nuclei differs from that which would be obtained from a collection of nucleons with properties unmodified from their free-space values. We stress, however, that if the properties of the nucleon are modified in the nucleus there are important consequences for the analysis of other, more traditional, nuclear physics experiments. We discuss nuclear structure functions near the (nucleon) quasielastic peak and show how modified nucleon properties can explain the quenching of the longitudinal response. Most of our discussion, however, is devoted to a study of nuclear charge distributions. We stress that what is being measured in these experiments is the quark charge distribution. We also provide approximate expressions for the quark charge density in terms of modified nucleon electromagnetic form factors and the nucleon density matrix. Numerical estimates of the size of various effects due to the modification of nucleon properties in nuclei are presented. Well-known difficulties found in relating theoretical charge distributions with those measured in electron scattering may be resolved in this approach since we show that only if the nucleon electromagnetic form factors are unmodified in nuclei is the standard analysis correct. Specifically we show that in the case of ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$, certain well-known problems found in relating theoretical and experimental charge densities can be largely resolved by using the matter densities of modern relativistic mean-field theories and the modified electromagnetic form factors we have calculated in an earlier work.