Results from the first science run of the ZEPLIN-III dark matter search experiment

The ZEPLIN-IIIexperiment in the Palmer Underground Laboratory at Boulby uses a 12 kg two-phase xenon time-projection chamberto search for the weakly interacting massive particles( WIMPs) that may account for the dark matter of our Galaxy. The detector measures both scintillation and ionization produced by radiation interacting in the liquid to differentiate between the nuclear recoilsexpected from WIMPsand the electron- recoilbackground signals down to {approx}10 keV nuclear- recoilenergy. An analysis of 847 kg{center_dot}days of data acquired between February 27, 2008, and May 20, 2008, has excluded a WIMP-nucleon elastic scattering spin-independent cross section above 8.1x10{sup -8} pb at 60 GeVc{sup -2} with a 90% confidence limit. It has also demonstrated that the two-phase xenontechnique is capable of better discrimination between electron and nuclear recoilsat low-energy than previously achieved by other xenon-based experiments.