LUX and LZ - the direct search for Dark Matter and novel approaches to low-energy calibration

by Dr Richard Gaitskel
(Brown University)

Particle dark matter is thought to be the overwhelming majority of the matter in the Universe. Its gravitational contribution overwhelms that from the ordinary matter that we, the earth and the stars, are composed of. However, we still have no convincing direct evidence for the existence of particle dark matter. This may soon change... I will discuss the LUX Experiment which has world leading results in the search for WIMPs (weakly interacting massive particles). LUX is a 350 kg liquid Xe time projection chamber, and is operating underground at the Sanford Lab, Homestake, SD. I will also discuss LZ the next generation 8 tonne liquid Xe detector, progeny of LUX and ZEPLIN, that will be constructed and then operated at Sanford Lab, scheduled to first take data in 2019. In order to be confident that we are directly detecting dark matter, and not misidentifying backgrounds, we need to understand the response of our detectors. The field is littered with many false detections. I will discuss some of the novel techniques that LUX has developed to better calibrate the detector response. This will include a description of the novel calibration of nuclear recoils (NR) in liquid xenon (LXe) performed in situ in the LUX detector using mono-energetic 2.45 MeV neutrons produced by a D-D neutron generator. This technique was used to measure the NR charge yield in LXe (Qy) to <1 keV recoil energy with an absolute determination of the deposited energy. The LUX result is a factor of lower in energy compared to any other previous measurement in the field, and provides a significant improvement in calibration uncertainties. Strategies for extending this calibration technique to even lower energies and smaller uncertainties will be discussed. This has a significant impact on LUX's ability to look for low mass WIMPs.