Radioactivity Backgrounds in ZEPLIN-III

Understand

We examine electron and nuclear recoil backgrounds from radioactivity in the ZEPLIN-III dark matter experiment at Boulby.

• The rate of low-energy electron recoils in the liquid xenon WIMP target is 0.75$\pm$0.05 events/kg/day/keV, which represents a 20-fold improvement over the rate observed during the first science run.
• Energy and spatial distributions agree with those predicted by component-level Monte Carlo simulations propagating the effects of the radiological contamination measured for materials employed in the experiment.
• Neutron elastic scattering is predicted to yield 3.05$\pm$0.5 nuclear recoils with energy 5-50 keV per year, which translates to an expectation of 0.4 events in a 1-year dataset in anti-coincidence with the veto detector for realistic signal acceptance.