Nuclear recoil limits from the ZEPLIN I liquid xenon WIMP dark matter detector

The ZEPLIN I detector is a zero field liquid xenon detector used in the direct search for Galactic WIMP dark matter and has been operated at 2800 mwe depth in the Boulby mine underground facility in the UK. Discrimination between the types of interaction within the liquid xenon volume is performed through measurement of the time constant of the scintillation light, nuclear recoils being characterized by a faster time constant than the predominant background from gamma and beta events. The detector design is outlined, with a discussion of the detection efficiencies and analysis procedure, leading to a 90% c.l. spin independent cross-section upper limit of 1.1 × 10−6 pb at 60 GeV WIMP mass.