Scaling Variable for Nuclear Shadowing in Deep-Inelastic Scattering

A new scaling variable is introduced in terms of which nuclear shadowing in deep-inelastic scattering is universal, i.e. independent of $A$, $Q^2$ and $x$. This variable can be interpreted as a measure of the number of gluons probed by the hadronic fluctuations of a virtual photon during their lifetime. The shadowing correction grows at small $x$ substantially less steeply than is suggested by the eikonal approximation. This results from the fact that shadowing is dominated by soft rather than hard interactions.