Performance of the veto detector incorporated into the ZEPLIN-III experiment

Abstract

The ZEPLIN-III experiment is operating in its second phase at the Boulby Underground Laboratory in search of dark matter WIMPs. The major upgrades to the instrument over its first science run include lower background photomultiplier tubes and installation of a plastic scintillator veto system. Performance results from the veto detector using calibration and science data in its first six months of operation in coincidence with ZEPLIN-III are presented. With fully automated operation and calibration, the veto system has maintained high stability and achieves near unity live time relative to ZEPLIN-III. Calibrations with a neutron source demonstrate a rejection of 60% of neutron-induced nuclear recoils in ZEPLIN-III that might otherwise be misidentified as WIMPs. This tagging efficiency reduces the expected untagged nuclear recoil background from neutrons during science data taking to a very low rate of ~0.2 events per year in the WIMP acceptance region. Additionally, the veto detector provides rejection of 28% of gamma-ray induced background events, allowing the sampling of the dominant source of background in ZEPLIN-III - multiple scatter gamma-rays with rare topologies. Since WIMPs will not be tagged by the veto detector, and tags due to gamma-rays and neutrons are separable, this population of multiple scatter events may be characterised without biasing the analysis of candidate WIMP signals in the data.

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• Inelastic Dark Matter
• New results from DAMA/LIBRA
• Limits and Confidence Intervals in the Presence of Nuisance Parameters
• Results from the First Science Run of the ZEPLIN-III Dark Matter Search Experiment
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• The ZEPLIN-III dark matter detector: instrument design, manufacture and commissioning
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• Limits on inelastic dark matter from ZEPLIN-III
• Limits on spin-dependent WIMP-nucleon cross-sections from the first ZEPLIN-II data
• Simulation of neutrons produced by high-energy muons underground
• The ZEPLIN-III dark matter detector: performance study using an end-to-end simulation tool
• The ZEPLIN-III Anti-Coincidence Veto Detector

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• WIMP-nucleon cross-section results from the second science run of ZEPLIN-III
• Single electron emission in two-phase xenon with application to the detection of coherent neutrino-nucleus scattering
• Nuclear recoil scintillation and ionisation yields in liquid xenon from ZEPLIN-III data
• Measurement and simulation of the muon-induced neutron yield in lead
• Quenching Factor for Low Energy Nuclear Recoils in a Plastic Scintillator
• Radioactivity Backgrounds in ZEPLIN-III
• Direct Dark Matter Detection - A spin 3/2 WIMP candidate
• Some properties of dark matter field in the complex octonion space
• A Liquid Scintillation Detector for Radioassay of Gadolinium-Loaded Liquid Scintillator for the LZ Outer Detector
• Debris Flows in Direct Dark Matter Searches-The modulation effect
• Inelastic WIMP-nucleus scattering to the first excited state in ${}^{125}$Te
• Heavy sterile neutrino in dark matter searches
• Performance data from the ZEPLIN-III second science run
• DM-Ice: Current Status and Future Prospects
• Renormalization of the Spin-dependent WIMP scattering off nuclei