The total interaction cross sections of the relativistic π + π − -atoms with ordinary atoms are obtained in the eikonal approach which takes into consideration all multiphoton exchange processes. The contribution of these processes strongly depends on the atom nucleus charge Z and varies from 1.5% for titanium (Z = 22) to 14% for tantalum (Z = 73). The formulae derived are applicable for an arbitrary initial state of the π + π − -atom.

No abstract

The Born approximation, one photon exchange, used for DIS is subject to virtual radiative corrections which are related to the long-range Coulomb forces. They may be sizeable for heavy nuclei since Zα is not a small parameter. So far these corrections are known only for two processes, elastic scattering and bremsstrahlung on the Coulomb field of a point-like target. While the former amplitude acquires only a phase, in the latter case the cross section is modified also. Although the problem of Coulomb corrections for DIS on nuclei is extremely difficult, it should be challenged rather than 'swept under the carpet'. The importance of these radiative corrections is questioned in present paper. We show that in the simplest case of a constant hadronic current the Coulomb corrections provide a phase to the Born amplitude, therefore the cross section remains the same. Inclusion of more realistic hadronic dynamics changes this conclusion. The example of coherent production of vector mesons off nuclei reveals large effects. So far a little progress has been made deriving lepton wave functions in the Coulomb field of an extended target. Employing available results based on the first-order approximation in Zα, we conclude that the Coulomb corrections are still important for heavy nuclei. We also consider an alternative approach for extended nuclear targets, the eikonal approximation, which we demonstrate to reproduce the known exact results for Coulomb corrections. Calculating electroproduction of vector mesons we again arrive at a large deviation from the Born approximation. We conclude that one should accept with caution the experimental results for nuclear effects in DIS based on analyses done in the Born approximation.

High-energy Coulomb corrections to the parameters of the Molière multiple scattering theory are obtained. Numerical calculations are presented in the range of the nuclear charge number of the target atom 6 Z 92. It is shown that these corrections have a large value for sufficiently heavy elements of the target material and should be taken into account in describing high-energy experiments with nuclear targets.

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 the interaction and take only the qq component of the hadronic structure of the photon into account. We use a representation in which the qq-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 show that higher order scattering terms have a strong influence on the total cross section σ γ * A tot . The aim of this paper is to give a detailed derivation of the formula for the total cross section.PACS. 11.80.Fv Approximations (eikonal approximation, variational principles, etc.) 11.80.La Multiple scattering 13.60.Hb Total and inclusive cross sections (including deep-inelastic processes) 25.20.Dc Photon absorption and scattering