Abstract:
Discovery of the nature of dark matter is internationally recognised as one of the greatest contemporary challenges in science, fundamental to our understanding of the Universe. Weakly Interacting Massive Particles (WIMPs) that arise naturally in several models of physics beyond the Standard Model are promising candidates. The discovery of galactic WIMPs would therefore enlighten two of the outstanding problems of modern physics - the matter composition of the Universe and the extrapolation of the Standard Model of particle physics to GUT scales. Although no definitive signal has yet been discovered, the worldwide race towards direct detection has been dramatically accelerated by the remarkable progress and evolution of liquid xenon (LXe) time projection chambers (TPCs).
I will present the current status in the worldwide hunt for WIMPs, and focus on the LXe TPC based LUX experiment that recently completed operation in the Davis Cavern of the SURF laboratory, USA. LUX has set the most stringent constraints on WIMP-nucleon interactions to-date, at 1.1x10-46 cm2 for a 50 GeV/c2 WIMP mass (90% C.L.), having found no evidence of signal above expected background in a complete exposure of 3.4x10^4 kg.days. As well as extending the range of WIMP searches some 20 times into unexplored electroweak parameter space, LUX also rules out the interpretation of hints of signal detected in other experiments as arising from low-mass WIMPs. Finally, I will present the multi-tonne successor to LUX: the LZ experiment, currently under construction. This instrument will have sensitivity ideally matched to explore the bulk of the remaining theoretically favoured electroweak phase space towards galactic Dark Matter discovery.