Observational studies of the rotation of galaxies and groups of galaxies
strongly suggest the existence of a dominating amount of matter invisible at
any electromagnetic wavelengths. One of the favoured forms of this
"missing mass", both theoretically and observationally, is the WIMP
(Weakly Interacting Massive Particle). These cold WIMPs are expected to be
scattered by the nuclei of typical detector material at a rate of less than one
per kg per day, yielding energy depositions in the 1-50 keV energy range.
ZEPLIN-III is a two-phase (liquid/gas) xenon detector looking for galactic WIMP
dark matter at the Boulby Underground Laboratory, North Yorkshire, UK, at a
depth of 1100 m. At this depth the cosmic-ray background is reduced by a
factor of a million. The WIMP target consists of 12 kg of cold liquid
xenon topped by a thin layer of xenon gas. These are viewed by an array of 31
photomultiplier tubes immersed in the liquid.
The detector operates at higher electric fields than other, similar
systems, namely its predecessor ZEPLIN-II, and provides high-precision
reconstruction of the interaction point in three dimensions. Together with the
low-background construction (mainly high-purity copper), these features will
give ZEPLIN-III higher sensitivity in direct WIMP searches.
The ZEPLIN-III Collaboration includes the University of Edinburgh,
Rutherford Appleton Laboratory, Imperial College London, LIP-Coimbra (Portugal)
and ITEP-Moscow (Russia).
In memoriam Vadim Nikolaevich
Lebedenko (1939-2008)