The ZEPLIN III liquid xenon dark matter detector is designed to potentially discover
the WIMP - a supersymmetric galactic dark matter candidate. This thesis presents
experimental results of the ZEPLIN III commissioning studies, in preparation for
the first and second underground science runs.
Data acquired on the surface, at the Imperial College London laboratories, were
used to characterise the instrument’s response in terms of light yield (LY) and
single photoelectron (SPE) spectra. A zero-field LY was measured as 7.42±0.37
phe/keV and 18.12±0.91 phe/keV in dedicated single- and dual-phase high yield
configurations, respectively, consistent with Monte Carlo simulations. Mean SPE
measured pulse areas ranged from 41.78±1.55 Vps to 52.37±1.59 Vps, depending
on the method employed. A 3-D position reconstruction was verified and, significantly,
no evidence of a potentially-contaminating background -population was
observed. This study directly lead to critical development of the DAQ software and
hardware configuration. The PMT array was confirmed as responsive and, crucially,
the particle discrimination principle was demonstrated. Zero-field LYs of (4.6-4.7)
±0.5 phe/keV were recovered from the centre of the chamber, exceeding simulation
predictions. With-field (3.01 kV/cm in the liquid) LYs of (1.2-1.8) ±0.3 phe/keV
from the liquid scintillation (S1) and an electroluminescence yield (S2) of (98-140)
±35 phe/keV from the gas phase were also determined.
ZEPLIN III was deployed in the Boulby Underground Laboratory, UK and demonstrated
successful operation at high field (up to 3.79 kV/cm in the liquid), in situ.
An alternative Poisson method for obtaining single photoelectron distributions was
developed by the ZEPLIN collaboration. The origin of long- events in surface
data was investigated and ultimately resolved as an artefact of early versions of
the data reduction software. An S1 zero-field LY of 4.72±0.10 phe/keV, obtained
with a 57Co external source, was recovered for the centre of the chamber. The instrument’s
energy resolution was evaluated and a novel parameterisation approach,
developed by the author, yielded sigma=1.08±0.06
p
E(keV ) with a dominant stochastic
term. A ‘flat-fielding’ method was established, proving to minimise the resolution
significantly, yielding 8.6% and 7.3% for S1 and S2, respectively, in the fiducialised
anti-correlated energy channel. This flat-fielding recipe, along with construction
of the light collection correction matrices, formed the basis of the final procedures
subsequently applied to first science run data-sets.