Background Simulations and WIMP Search with Galactic Signature Dark Matter Experiments

There is now compelling evidence that ordinary baryonic matter only represents 15% of the matter content of the Universe. Observational results suggest that the remaining 85% may be constituted of dark matter possibly in the form of weakly interacting massive particles (WIMPs). One of the potential ways to detect these WIMPS is to look for their scattering interactions with nuclei. This is the basis
of direct detection experiments. In particular, galactic signature direct detection experiments look for the characteristic properties of the WIMP signal.
The current landscape of galactic signature experiments is dominated by two main types of experiments. Firstly, NaI (Tl) detectors are searching for the annual modulation
of the WIMP recoil rate induced by the revolution of the Earth. Secondly, directional time projection chambers (TPCs) can reconstruct the momentum of the incoming scattering particle and determinate whether its origin is compatible with the WIMP wind. In this thesis, both types of experiments are addressed.
For these rare-event searches, the performance of the detector is dictated by two linked parameters, the mass of target materials and the rate of background events.
A new generation of galactic signature experiments is currently being developed.
This work addresses the issue of the background levels through the use of Monte-Carlo simulations to predict the event rate associated with the different backgrounds.
In the context of the COSINE experiment, these simulations investigate the neutron background in the detector and compare the associated rate to a theoretical model which proposes that neutrons may be responsible for the positive signal seen by the DAMA experiment. Otherwise, for the proposed CYGNUS experiments, these simulations are done in a way to facilitate the design effort of the collaboration
and orientate the blueprints towards detectors which could potentially achieve background event rates below 1 per year.
These efforts may potentially lead to the creation of background-free experiments larger than the DRIFT-IId TPC. Background-free status was achieved in DRIFT with the discovery of minority carriers in 2013. This thesis presents the current world-leading directional limit on the spin-dependent WIMP-proton cross section achieved with the DRIFT-IId detector. The recent detection of fast neutrons from
the rock at the Boulby underground laboratory is also discussed. This is the first ever measurement of the concentration of radioisotopes in an underground laboratory
using a TPC. This thesis is considering the impact that this new technique may have on future dark matter searches and how it may provide a new tool for neutron metrology in nuclear physics.