Observation of Shadowing in the Virtual-Photon Total Hadronic Cross Section on Nuclei

Abstract

We have measured the total hadronic cross section of virtual photons incident on carbon, copper, and lead in the region $Q^2=0.01-30\mathrm{}$ Ge${\mathrm{V}}^2$ and $\nu =40-200\mathrm{}$ GeV. A 209-GeV/c muon beam was used as a source of virtual photons. The results indicate shadowing of the virtual photons below $Q^2=1\mathrm{}$ Ge${\mathrm{V}}^2$ and a decrease of shadowing for $Q^2>3\mathrm{}$ Ge${\mathrm{V}}^2$. The shadowing persists to larger $Q^2$ than indicated by experiments at lower $\nu$.