Nuclear Shadowing in DIS at Moderately Small xBx_B

In the rest frame of the nucleus, shadowing is due to hadronic fluctuations of the incoming virtual photon, which interact with the nucleons. We expand these fluctuations in a basis of eigenstates of interaction and take only the $q\bar q$ component of the hadronic structure of the photon into account. We use a representation in which the $q\bar q$-pair has a definite transverse size. Starting from the Dirac equation, we develop a path integral approach that allows to sum all multiple scattering terms and accounts for fluctuations of the transverse size of the pair, as well as for the finite lifetime of the hadronic state. First numerical results hep-ph/9807211 have shown that higher order scattering terms have a strong influence on the total cross section $\sigma^{\gamma^*A}_{tot}$. The aim of this paper is to give a detailed derivation of the formula for the total cross section.Comment: 10 pages, 1 figure, uses svjour, svepj, minor misprints corrected, results unchange

Relating parton model and color dipole formulation of heavy quark hadroproduction

At high center of mass energies, hadroproduction of heavy quarks can be expressed in terms of the same color dipole cross section as low Bjorken-x deep inelastic scattering. We show analytically that at leading order, the dipole formulation is equivalent to the gluon-gluon fusion mechanism of the conventional parton model. In phenomenological application, we employ a parameterization of the dipole cross section which also includes higher order and saturation effects, thereby going beyond the parton model. Numerical calculations in the dipole approach agree well with experimental data on open charm production over a wide range of energy. Dipole approach and next to leading order parton model yield similar values for open charm production, but for open bottom production, the dipole approach tends to predict somewhat higher cross sections than the parton model.Comment: 16 pages, 4 figure