Pion density in nuclei and deep-inelastic lepton scattering

Recent data indicate that quark densities in a high-$A$ nucleus differ significantly from those measured in the free-nucleon case. We examine whether this effect can be explained in terms of deepinelastic scattering from mesons responsible for nuclear binding. Although features of the data are reproduced qualitatively, we are unable to approach a quantitative description of the magnitude of the experimental effect at small $x$ unless we postulate an enhanced pion density of about 0.4 extra pions per nucleon (roughly three times that provided by conventional nuclear models), and/or make assumptions about the small-$x$ behavior of the meson structure function which are inconsistent with available data. These conclusions are insensitive to the manner in which we impose momentum conservation. The slope of the ratio of structure functions vs $x$ is reproduced easily in the range $0.05<x<0.5$. We speculate that a quantitative fit to the data requires an "intrinsic" enhancement of the nucleon structure function due to the nuclear medium as well as scattering from the mesons associated with binding.