Precise predictions and new insights for atomic ionization from the Migdal effect

The scattering of neutral particles by an atomic nucleus can lead to electronic ionization and excitation through a process known as the Migdal effect. We revisit and improve upon previous calculations of the Migdal effect, using the Dirac-Hartree-Fock method to calculate the atomic wave functions. Our methods do not rely on the use of the dipole approximation, allowing us to present robust results for higher nuclear recoil velocities than was previously possible. Our calculations provide the theoretical foundations for future measurements of the Migdal effect using neutron sources, and searches for dark matter in direct detection experiments. We show that multiple ionization must be taken into account in experiments with fast neutrons, and derive the semi-inclusive probability for processes that yield a hard electron above a defined energy threshold. We present results for the noble elements up to and including xenon, as well as carbon, fluorine, silicon and germanium. The transition probabilities from our calculations are publicly available.

Automated summary

In this study, we revisit and improve calculations of the Migdal effect by using the Dirac-Hartree-Fock method. Unlike previous studies, our approach does not rely on the dipole approximation, allowing for more accurate results at higher nuclear recoil velocities. These calculations provide a theoretical basis for future measurements of the Migdal effect using neutron sources and for the search for dark matter in direct detection experiments. We also highlight the importance of considering multiple ionization in experiments with fast neutrons and derive the semi-inclusive probability for processes that produce high-energy electrons above a defined threshold. Our results include noble elements up to xenon, as well as carbon, fluorine, silicon, and germanium, with the transition probabilities publicly available.