Ionization of atoms by slow heavy particles, including dark matter
  Atoms and molecules can become ionized during the scattering of a slow, heavy
particle off a bound electron. Such an interaction involving leptophilic weakly
interacting massive particles (WIMPs) is a promising possible explanation for
the anomalous 9 sigma annual modulation in the DAMA dark matter direct
detection experiment [R. Bernabei et al., Eur. Phys. J. C 73, 2648 (2013)]. We
demonstrate the applicability of the Born approximation for such an interaction
by showing its equivalence to the semiclassical adiabatic treatment of atomic
ionization by slow-moving WIMPs. Conventional wisdom has it that the ionization
probability for such a process should be exponentially small. We show, however,
that due to nonanalytic, cusp-like behaviour of Coulomb functions close to the
nucleus this suppression is removed, leading to an effective atomic structure
enhancement. Crucially, we also show that electron relativistic effects
actually give the dominant contribution to such a process, enhancing the
differential cross section by up to 1000 times.
