From dark to light, ionization and heat. An inquiry concerning the complementary of dark matter electron and dark matter nuclear scattering

Abstract

The recent development of direct detection experiments can be divided into two main approaches: On the one hand, to give weakly interacting massive particles (WIMPs) as Elizabeth Gibney puts it "a final chance to reveal itself", on the other hand, to reach out for candidates beyond the WIMP-paradigm. In this regard, new possibilities in the search for dark matter arise by simultaneously lowering detection thresholds successively and exploiting new kinds of atomic or nuclear phenomena besides the well known dark matter nucleus scattering, namely dark matter electron scattering, the Migdal effect or Bremsstrahlung. While the interaction of dark matter particles and target materials differs for each effect, the observable quantity for each of these phenomena ultimately is the energy deposited in the detector. For dark matter nucleus scattering, some of the kinetic energy of a dark matter particle is transferred to the nucleus of a Standard Model particle. This energy deposition is then converted to measurable signals i.e. ionization, scintillation light or heat. The Migdal effect on the other hand induces ionization signals in addition to the nuclear recoil (3-body process), when a sub-GeV dark matter particle scatters off the nucleus. Finally, when dark matter couples directly to electrons (i. e. electron scattering), ionization and excitation in the electron system of the target atoms can be detected. This means that, depending on the dark matter mass and its coupling to the Standard Model particles, a variety of detection avenues exist at direct detection experiments. The deposited energy of dark matter particles within the detector can mainly (with the exeption of bubble chambers) be measured via scintillation, ionization or heat. Understanding the limits of each effect therefore becomes a key aspect of exploiting the complete potential of current and future direct detection experiments. This is especially the case for dark matter scenarios that go beyond the WIMP paradigm by involving e.g. multiple components. This thesis addresses a comprehensive analysis of the above described dominating theoretical effects induced by dark matter interaction with the Standard Model constituents, primarily taking liquid Xenon as an example. In order to achieve this, the astrophysical parameters, the possible ways of interaction and the detector response for each interaction need to be computed. This results in anticipated interaction rates for each effect and detector. Comparing these anticipated detection rates allows us to draw conclusions for possible blind spots and challenges in setting direct detection limits for particular dark matter scenarios.