IOP 2014 Joint HEPP & APP Group Meeting

Apr 7 – 9, 2014
Royal Holloway, University of London
Europe/London timezone
Institute of Physics 2014 Joint High Energy Particle Physics and Astro Particle Physics Groups Annual Meeting

Delayed Coincidence Analysis for Determining the 85Kr Background in LUX

Apr 8, 2014, 1:30 PM
15m
Room D (Windsor Building)

Room D

Windsor Building

contributed talk Particle Astrophysics, Current and Future

Speaker

$^{85}$Kr is an anthropogenic radioisotope which makes up a very small fraction of the Kr abundance in the atmosphere, and contributes to the background in double-phase xenon detectors searching for WIMP dark matter. It has a half-life of 10.8 years and decays predominantly via a $\beta^-$ decay with an endpoint of 687 keV. Commercially available xenon procured for LUX contained 130 ppb g/g Kr/Xe, which would lead to unacceptably high background. Before the start of the experiment this was reduced to 4±1 ppt g/g by chromatographic separation, as this noble gas is not removed further by the standard purification methods during operation. Current measurements of the $^{85}$Kr concentration use gas sampling assays to determine the overall Kr content with ppt sensitivity, and then assume a ratio of $^{85}$Kr/Kr as measured in the atmosphere. It is prudent to try to assess this background by determining the $^{85}$Kr content directly. This is possible due to a low branching ratio $\beta^-$ decay providing a delayed $\beta - \gamma$ coincidence with $T_{1/2}$ ~1 $\mu$s. We present results from a search of these rare decays performed on the LUX data used to derive the WIMP result previously published.