Inclusive Scattering of 500-MeV Protons and Pionic Enhancement of the Nuclear Sea-Quark Distribution

We have measured a complete set of polarization-transfer observables in the inclusive scattering of 500-MeV protons from ${}_{}{}^2{}_{}{}^{}\mathrm{H}$ and Pb at $q=1.75\mathrm{}$ ${\mathrm{fm}}^{-1\mathrm{}}$. Axial longitudinal and transverse response functions derived from these data show no differences between Pb and ${}_{}{}^2{}_{}{}^{}\mathrm{H}$. This implies no enhancement of the nuclear pion field in heavy nuclei and consequently that models of the low-$x$ $A$ dependence of certain nuclear structure functions requiring such an enhancement are unlikely to be correct.