There is considerable evidence for the existence of dark matter in the universe, however what this is constituted of remains an unanswered question. A favoured candidate to solve this problem is the Weakly Interacting Massive Particle, or WIMP. An example of WIMP is the lightest supersymmetric particle (LSP), predicted by supersymmetry and which fits all the necessary criteria for it to be dark matter. The LUX-ZEPLIN experiment seeks to detect WIMP dark matter through the use of a liquid xenon dual-phase xenon time projection chamber. This technology measures the light and charge signals from WIMP-nucleon interactions at low energies. Whilst the LZ experiment is yet to provide evidence for WIMP interactions, it has set world leading limits on the WIMP-nucleon cross sections.
A key part of the success of the LZ experiment is the understanding of the background events in the detector. This involves reducing the possible backgrounds as low as possible, and incorporating the remaining backgrounds into a background model. One of the remaining backgrounds in the detector is that from neutron activated xenon. When exposed to neutrons, the stable xenon in the detector can be turned into radioactive isotopes such as 127Xe, 129mXe and 131m Xe. The decay rates of these isotopes in the data taken during LZ’s first science run have been measured to inform the overall background model in the detector.
Radioactive xenon isotopes can be produced by exposure to cosmogenic neutrons, or those emitted by calibration sources. LZ uses three neutron sources in calibrations, a deuterium-deuterium generator, an AmLi source, and an AmBe source. The use of these sources causes an increase in the decay rate of these three xenon isotopes. This increase in the decay rate has been used to calculate the production rate of these radioactive isotopes from the various calibration sources, which has been compared to expectations from calculations and simulations. In general these predictions were in good agreement with the results measured from LZ data, especially the production of 131m Xe.
