Theoretical predictions of wimp-nucleus and neutrino-nucleus scattering in context of dark matter direct detection

Abstract

The nature of dark matter is at present an open question. Assuming the main component of dark matter consists of weakly interacting massive particles (WIMPs), directly detecting such particle via a scattering process with an atomic nucleus would be a strong probe into properties of dark matter. So far direct detection experiments have not provided a conclusive signal of dark matter. Traditionally the experiments aim to detect a coherent, spin- independent, elastic scattering signal which is enhanced by the square of the nuclear mass number. If the coherent channel is for some reason suppressed for WIMP-nucleus interactions, then spin-dependent interactions become important. In this thesis we focus on spin-dependent interactions of WIMPs scattering off two possible detector nuclei 83Kr and 125Te. These nuclei are particularly interesting for inelastic scattering due to their very low-lying first excited states. The nuclear structure of the target nuclei was computed within the nuclear shell model. Our analysis shows that, although the 9.4 keV excited state of 83Kr has some kinematical advantages, the obtained elastic and inelastic scattering event rates do not encourage to build a detector based on 83Kr. On the other hand, 125Te appears to possess nuclear structure very sensitive to spin-dependent interactions based on the results presented in this thesis. A detector based on 125Te might open some new possibilities especially for inelastic scattering searches. With increasing size and sensitivity direct detection experiments will soon become sensitive to coherent scattering of astrophysical neutrinos. This gives rise to the problem commonly referred to as the neutrino floor, which will prevent the experiments probing lower WIMP-nucleon cross sections after the neutrino background becomes visible in the data. In this thesis we present the first calculations of neutrino-nucleus scattering cross sections in a microscopic nuclear framework for most of the stable Xe isotopes. We perform the nuclear structure calculations in the framework of the (proton-neutron) quasiparticle random-phase approximation ((pn)QRPA) for states of even-mass nuclei and in the microscopic quasiparticle-phonon model for states of odd-mass nuclei. We present results for the total cross sections for neutral-current and charged-current processes as a function of the neutrino energy as well as for the solar 8B neutrino and supernova neutrino and antineutrino profiles. This thesis consists of five publications and an overview part. Articles I–III discuss WIMPs scattering off 83Kr and 125Te and articles IV and V discuss neutrino-nucleus scattering in context of Xe dark matter detectors. In the overview part the theoretical formalism and results of all five publications are drawn together in a coherent and concise manner.