Long-Range Coulomb Forces in DIS: Missed Radiative Corrections?

摘要

The Born approximation, one photon exchange, used for DIS is subject tovirtual radiative corrections which are related to the long-range Coulombforces. They may be sizeable for heavy nuclei since Z\alpha is not a smallparameter. So far these corrections are known only for two processes, elasticscattering and bremsstrahlung on the Coulomb field of a point-like target.While the former amplitude acquires only a phase, in the latter case the crosssection is modified also. Although the problem of Coulomb corrections for DISon nuclei is extremely difficult, it should be challenged rather than 'sweptunder the carpet'. The importance of these radiative corrections is questionedin present paper. We show that in the simplest case of a constant hadroniccurrent the Coulomb corrections provide a phase to the Born amplitude,therefore the cross section remains the same. Inclusion of more realistichadronic dynamics changes this conclusion. The example of coherent productionof vector mesons off nuclei reveals large effects. So far a little progress hasbeen made deriving exact lepton wave functions in the Coulomb field of anextended target. Employing available results based on the first-orderapproximation in Z\alpha, we conclude that the Coulomb corrections are stillimportant for heavy nuclei. We also consider an alternative approach forextended nuclear targets, the eikonal approximation, which we demonstrate toreproduce the known exact results for Coulomb corrections. Calculatingelectroproduction of vector mesons we again arrive at a large deviation fromthe Born approximation. We conclude that one should accept with caution theexperimental results for nuclear effects in DIS based on analyses done in theBorn approximation.