Charge Transfer from the Negative-Energy Continuum: Alternative Mechanism for Pair Production in Relativistic Atomic Collisions

As an alternative mechanism for bound-free electron-positron pair production, the transfer of a negative-energy electron in the Coulomb field of one of the collision partners to a bound state of the other is considered, supplementing the usually adopted view that an electron is excited from a negative-energy state to a bound state of the same atom. Under simplifying assumptions, analytic expressions for the differential and total cross sections can be derived, which explicitly exhibit the dependencies on the nuclear charges and show a surprisingly strong increase with the collision energy.