MRI Instrument Development for Liquid Xenon Dark Matter Searches: An Atom Trap Trace Analysis System to Measure Ultra-Low Krypton Contamination in Xenon

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The leading hypothesis for the nature of dark matter is that it consists of new elementary particles produced moments after the Big Bang, generally referred to as Weakly Interacting Massive Particles. One way to detect them in an Earth-bound experiment is to measure the low energy nuclear recoils they produce in rare interactions with normal matter. A key requirement is control and reduction of background to an ultra-low level. Traces of radioactive isotopes in noble liquid targets contribute an intrinsic background. For Xenon targets, the isotope of concern is Krypton-85. Even though the abundance of this isotope compared to normal Krypton is extremely small, the Krypton contamination must be reduced to the part per trillion (ppt) level in order for the Krypton-85 background to be negligible in an experiment like XENON. The Atom Trap Trace Analysis (ATTA) method has the potential to accomplish this task.This award is to develop an ATTA system based on laser cooling, trapping, and counting single atoms, with the specific purpose of determining the number of radioactive Krypton atoms in Xenon samples and hence verifying the reduction of the Krypton/Xenon contamination to the ppt level. This three-year instrumentation development project is a collaborative effort between the XENON Dark Matter group and the atomic, molecular, and optical (AMO) group. The program will have a broad scientific impact on dark matter searches and other low background physics experiments based on noble liquids. The project connects laser cooling and trapping of single atoms with the most fundamental question in physics today, the nature of dark matter. The proposed research can impact society in many ways: cold atom techniques are used widely in the field of quantum information and ultra-sensitive Krypton analysis is used in geology for archaeological dating and studies of transport processes in the atmosphere, oceans and groundwater.