Migdal effect in dark matter direct detection experiments

Abstract

The elastic scattering of an atomic nucleus plays a central role in dark matter direct detection experiments. In those experiments, it is usually assumed that the atomic electrons around the nucleus of the target material immediately follow the motion of the recoil nucleus. In reality, however, it takes some time for the electrons to catch up, which results in ionization and excitation of the atoms. In previous studies, those effects are taken into account by using the so-called Migdal's approach, in which the final state ionization/excitation are treated separately from the nuclear recoil. In this paper, we reformulate the Migdal's approach so that the "atomic recoil" cross section is obtained coherently, where we make transparent the energy-momentum conservation and the probability conservation. We show that the final state ionization/excitation can enhance the detectability of rather light dark matter in the GeV mass range via the nuclear scattering. We also discuss the coherent neutrino-nucleus scattering, where the same effects are expected. *

Coherent elastic neutrino-nucleus scattering at the European Spallation Source

“…5) indicate that it is of O(10)%, comparable to that for CsI[Na] at room temperature [71]. An anomalous increase of the QF for alphas in CsI at low temperature [61,62], and the possible presence of coadjutant low-energy processes such as the Migdal effect [81], are a reminder of the need for a full QF characterization. We temporarily adopt an energy-independent value of 10% (Table I).…”

Direct detection and complementary constraints for sub-GeV dark matter

“…(3.1) for the minimal recoil energy adopted in the respective analysis, or by directly fitting to data provided by the experiment (for PandaX-II [27]). We note that carefully modelling inelastic scattering processes, resulting in the emission of a photon or an atomic electron, in principle allows to improve sensitivities in the few 100 MeV range [72][73][74]. There is also a number of proposed direct detection experiments, and ideas, that would probe even smaller cross sections in the mass range shown in figure 1, but the status of those is presently less certain (for a recent compilation, see ref.…”

Relation between the Migdal Effect and Dark Matter-Electron Scattering in Isolated Atoms and Semiconductors

“…The detectors typically lose sensitivity rapidly for DM masses below a few GeV, due to an inefficient energy transfer from the DM to the recoiling nucleus. However, the kinematic limitations are lifted when the DM-nucleus scattering process is accompanied by the irreducible simultaneous emission of a "bremsstrahlung" photon [1] or a "Migdal"-electron [2], or by considering alternative interactions such as DM-electron scattering [3]. In all cases the entire energy of relative motion between the atom and DM can in principle be transferred to the outgoing photon or electron.…”