In 1933, Fritz Zwicky realized that most of the matter in the Coma galaxy cluster was invisible. This finding launched a decades-long search for dark matter. Observation after observation has confirmed that if our current understanding of gravity holds that this mysterious matter must exist and in fact makes up about a quarter of our universe. However, we have yet to identify its specific nature.
A leading hypothesis is that dark matter is composed of Weakly Interacting Massive Particles, or WIMPs. LUX-ZEPLIN (LZ) will search for these particles by looking for evidence of WIMPs colliding with xenon nuclei inside the LZ detector, located 4850 feet underground in South Dakota's Sanford Underground Research Facility. (This search is similar to the one undertaken by the Cryogenic Dark Matter Search.)
The LZ group at SLAC plays a major role in designing, fabricating and carrying out the experiment. The laboratory recently invested in a central test platform that is being used to test LZ prototype detectors and will serve as a tool for R&D on fundamental xenon properties that will inform LZ and a potential next generation xenon dark matter experiment. The SLAC LZ group is also responsible for determining how to best purify the liquid xenon that will be used in the detector, since radio-pure xenon is needed to ensure that the experiment can see the very faint signal of a dark matter particle behind the higher rate from natural radiation sources.
SLAC also plays an important role in the LZ’s predecessor, the Large Underground Xenon (LUX) experiment. As one of the largest LUX groups, SLAC is heavily involved in the experiment’s operations and data analysis. LUX will operate until 2016 when it will be replaced with LZ, which will offer one-hundred-times better sensitivity to dark matter.