The ratio of cross sections for inelastic muon scattering on xenon and deuterium nuclei was measured at very low Bjorken x (0.000 02<${\mathit{x}}_{\mathrm{Bj}}$<0.25). The data were taken at Fermilab experiment E-665 with a 490 GeV/c muon beam incident on liquid deuterium and gaseous xenon targets. Two largely independent analysis techniques gave statistically consistent results. The xenon-to-deterium per-nucleon cross-section ratio is constant at approximately 0.7 for ${\mathit{x}}_{\mathrm{Bj}}$ below 0.003.

• Received 2 March 1992

DOI:https://doi.org/10.1103/PhysRevLett.68.3266