Atomic Many-Body Effects in Direct Detection of Dark Matters Using Germanium Detectors
Mukesh Kumar Pandey1*, Chih-Pan Wu1, Lakhwinder Singh3, Jiunn-Wei Chen1, Hsin-Chang Chi2, C. -P. Liu2, Henry T. Wong3
1Department of Physics, National Taiwan University, Taipei 10617, Taiwan
2Department of Physics, National Dong Hwa University, Shoufeng, Hualien 97401, Taiwan
3Institute of Physics, Academia Sinica, Taipei 11529, Taiwan
* Presenter:Mukesh Kumar Pandey,
Direct searches of dark matter (DM) look for signals as results of DM scattering off normal matter. We are able to perform systematic and controlled ab initio calculations of the detector response in the framework of the multi-configuration relativistic random-phase approximation (MCRRPA) once the interaction is given. Recently, the relativistic random-phase approximation(RRPA) has been applied, with remarkable successes, to photoexcitation and photoionization of closed-shell atoms and ions of high nuclear charge, such as heavy noble gas atoms, where the ground state is well isolated from the excited states. For other closed-shell systems, such as alkaline-earth atoms, which have low-lying excited states, such applications have been less successful, owing to the importance of two-electron excitations which are omitted in the RRPA. The MCRRPA theory is a generalization RRPA by using a multi-configuration wave function as the reference state which is suitable for treating photoexcitation and photoionization of closed-shell and certain open-shell systems of high nuclear charge. A detailed formulation of the MCRRPA has been given in a previous paper [1-2 and Reference in]. In a specific DM scattering process which a direct search detector is built to look for, what are the contributions from the electronic and nuclear degrees of freedom? Even though the current common practice in constraining DM interactions is one type at a time, it is necessary to keep in mind that events measured by a detector are a sum from all possible sources. Furthermore, it is desirable from the experimental point of view to determine which process and kinematic region would be best to constrain a certain type of DM interactions with electrons or nucleons. For this purpose, one has to rely on theoretical analysis. In this work, we try to address the above questions using the atom, Germanium—where most calculations can be carried out using MCRRPA Calculation—and study its scattering with nonrelativistic LDM particles of a MeV-GeV mass range. Our results of photoionization cross sections for Germanium detectors are in good agreement with the existing theoretical predictions and experimental results and we fixed it as benchmark for our calculation. These benchmark calculations justify a good understanding of how germanium detector respond to dark matter. Detail results will be presented at the meeting.
1. K.-N. Huang and W. R. Johnson, Phys. Rev. A 25, 634 (1982). .
2. Jiunn-Wei Chen et al, Phys. Rev. D 91, 013005 (2015). .

Keywords: Dark Matter, MCRRPA, Photo-ionization cross section, Germanium Detector