Narrow Results

ZEPLIN-III has been deployed at the Boulby Underground Laboratory and is now undergoing final commissioning tests ahead of the first fully-shielded run in search of dark matter WIMPs. We aim to improve on the discovery potential of other two-phase xenon detectors by means of lower background construction and better electron-nuclear recoil discrimination, partly aided by operation at a higher electric field. In this article we give an update on the status of the experiment and its future prospects in terms of sensitivity to WIMP-nucleon scalar interactions. We also highlight the potential of this technology for present and next-generation searches for rare events with small energy deposits.

An active veto detector to complement the ZEPLIN-III two phase Xenon, direct dark matter device is described. The design consists of 52 plastic scintillator segments, individually read out by high efficiency photomultipliers, coupled to a Gd loaded passive polypropylene shield. Experimental work was performed to determine the plastic scintillator characteristics which were used to inform a complete end-to-end Monte Carlo simulation of the expected performance of the new instrument, both operating alone and as an active veto detector for ZEPLIN-III. The veto device will be capable of tagging over 65% of expected coincident nuclear recoil events in the energy range of interest in ZEPLIN-III, and over 14% for gamma ray rejection (gamma and neutron rate is predicted by simulation), while contributing no significant additional background. In addition it will also provide valuable diagnostic capabilities. The inclusion of the veto to ZEPLIN-III will aid to significantly improve the sensitivity to spin independent WIMP-nucleon cross sections ~10^-9 pb.

ZEPLIN-III is a 12 kg two-phase xenon time projection chamber searching for weakly interacting massive particles (WIMPs) accounting for dark matter in our Galaxy. Scintillation and ionisation in the liquid differentiate between nuclear and electron recoils above ∼10 keVnr. 847 kg·days data acquired between Feb 27th and May 20th 2008 has excluded a coherent WIMP-nucleon scattering cross-section above 8:1 × 10⁻⁸ pb at 60 GeVc⁻²