Limits on spin-dependent WIMP-proton cross-sections using the DRIFT-IId directional dark matter detector

The nature of dark matter remains one of the biggest questions in physics today. Weakly Interacting Massive Particles (WIMPs) are a particularly well motivated candidate for the missing matter that makes up 85% of the mass of the Universe. The most promising method for an unambiguous proof of the existence of WIMPs is via detection of the predicted directional anisotropy. The DRIFT detector at the Boulby Underground Laboratory in the UK is the world’s first large scale directionally sensitive dark matter detector. This thesis presents work focussing on the ability of DRIFT to be competitive with non-directional detectors in exploring new spin-dependent WIMP interaction phase-space. Experimental efforts towards this are discussed, including the first calibration measurements of spin-dependent target gases in DRIFT, and development and implementation of an automated gas mixing system required for spin-dependent gas mixture operation. This thesis presents the first long-term study of backgrounds in DRIFT in which current limiting backgrounds are identified and studied, providing information crucial to future background reduction strategies. Developments of the WIMP analysis procedure are presented that result in an improved sensitivity to WIMP-mimicking neutron-induced nuclear recoils by a factor of 2.4. Data from the first runs with spin-dependent sensitive CS2-CF4 gas mixtures are presented with improved analysis methods. This thesis presents the first blind analysis results from a directionally sensitive dark matter detector with upper limits on the SD WIMP-proton interaction cross-section with a minimum of 0.93 pb for a 100 GeV WIMP