Coherence length and nuclear shadowing for transverse and longitudinal photons

Abstract

We study nuclear shadowing for transverse and longitudinal photons. The coherence length, which controls the onset of nuclear shadowing at small Bjorken-x is longer for longitudinal than for transverse photons. The light-cone Green function technique properly treats the finite coherence length in all multiple scattering terms. This is especially important in the region x>0.01, where most of the data exist. NMC data on shadowing in deep inelastic scattering are well reproduced in this approach. We also incorporate nonperturbative effects, in order to extrapolate this approach to small photon virtualities Q^2, where perturbative QCD cannot be applied. This way, we achieve a description of shadowing that is based only on quark and gluon degrees of freedom, even at low Q^2.