Target effects in negative-continuum assisted dielectronic recombination

The process of recombination of a quasi-free electron into a bound state of an initially bare nucleus with the simultaneous creation of a bound-electron--free-positron pair is investigated. This process is called the negative-continuum assisted dielectronic recombination (NCDR). In a typical experimental setup, the initial electron is not free but bound in a light atomic target. In the present work, we study the effects of the atomic target on the single and double-differential cross sections of the positron production in the NCDR process. The calculations are performed within the relativistic framework based on QED theory, with accounting for the electron-electron interaction to first order in perturbation theory. We demonstrate how the momentum distribution of the target electrons removes the non-physical singularity of the differential cross section which occurs for the initially free and monochromatic electrons.