DARK MATTER EXPERIMENTS

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					                              DARK MATTER EXPERIMENTS
                                                                                     Proposal 270
Particle Physics/Astrophysics collaboration

UK Dark Matter Collaboration:
Imperial College London                               University of Sheffield
University of Edinburgh                               CCLRC

Other participants in Boulby Dark Matter Collaboration:
Boston University                              Occidental College
ITEP (Moscow)                                  University of Rochester
LIP-Coimbra                                    Temple University
UCLA                                           Texas A&M
University of New Mexico

There is now overwhelming evidence in support of a ‘standard’ cosmology in which the Universe
has two dominant components, neither of which can be understood in a straightforward way. One
of these is a contribution to the raw energy content and it accounts for ~73% of the total energy
density in the Universe — the so-called ‘Dark Energy’. The next major contribution to the total
energy density is a matter density which seems to be in some unseen, weakly interacting and non-
relativistic form. This provides another ~22% and is called ‘Cold Dark Matter’. This leaves a
mere ~5% of the Universe to be made up from everything else and this is essentially provided by
all of the normal (baryonic) matter which we already know about. Individual galaxies are also
believed to be made up from a mix of cold dark matter and baryonic matter. There are many
suggestions about the possible form that the cold dark matter may take, but one of the more
persuasive is that it consists of relic stable elementary particles, such as axions (motivated from
CP violation) or neutralinos (motivated by supersymmetry theories).

An experimental programme to search for neutralinos, or more generically Weakly Interacting
Massive Particles (WIMPs), has been in progress since 1991, funded by PPARC. These
experiments search for nuclei recoiling in a detector target due to a WIMP scattering from them.
This elastic scattering process transfers energy to the recoiling nucleus, which produces
scintillation and ionisation in the target, which we measure simultaneously. We have two types of
instrument technology; liquid/gas xenon targets (ZEPLIN), measuring both scintillation and
ionisation, and low pressure gas targets measuring ionization tracks allowing direction to be
determined (DRIFT). First generation detectors of both types have completed operations.
ZEPLIN I has delivered one of the best results in the world (see Fig. 1) and DRIFT I has been a
successful demonstration of this pioneering new technology. The experiments are carried out in a
world-class underground facility established in the NaCl seam of Boulby potash mine near
Whitby, UK.

Boulby facility: The JIF-funded facility has now been upgraded to full class 2500 clean room
status (see Fig.2) in preparation for the imminent installation of the next three detectors, DRIFT
II, ZEPLIN II and ZEPLIN III. It has also been equipped with a class 1000 area for instrument
assembly/preparation and low-background material studies.

Xe programme (ZEPLIN):
• ZEPLIN-II (UKDMC, UCLA, Rochester, Texas A&M) and ZEPLIN-III
(UKDMC, ITEP, LIP-Coimbra) are both two-phase (liquid + gas) detectors with electric fields
extracting some of the primary ionisation electrons from the liquid into the gas phase. Final
assembly and commissioning of ZEPLINs II and III are in progress at RAL and ICL respectively.
– see Figs. 3,4 and 5.

• ZEPLIN-MAX: a 1 tonne design study is ongoing. This is drawing on experience gained from
ZEPLINs II and III. This work is also contributing to a European study within the ILIAS dark
matter network within framework 6.

DRIFT programme (Temple, Occidental, UKDMC, Boston, New Mexico):
Following on from the successful completion of DRIFT I operations, which have verified the
basic design principles, an improved and enlarged modular installation of DRIFT II is underway.
The first module has been fully commissioned on the surface and is now undergoing
commissioning underground (see Figs. 6 and 7).

Future plans: Although experimental dark matter searches are not tied to specific ‘beyond-the-
standard’ models, the most plausible range of SUSY parameters indicate a neutralino-nucleon
cross-section > 10-10 pb, providing physics motivation to aim for detector sensitivities at that
level. For a ‘standard’ dark matter galactic halo, that lower cross-section limit corresponds to
event rates ~ 10-4 per day per kg of target. Thus targets of tonne mass are required to deliver
statistically significant data on year time-scales. Multi-national proposals are being developed for
modular Xe arrays, building up to a 1 tonne target mass.

Recent publications
Monte Carlo studies of combined shielding and veto techniques for neutron background reduction in
underground dark matter experiments based on liquid noble gas targets
C.Bungau et al., Astropart. Phys. 23 (2005), 97-115
Limits on WIMP cross-sections from the NAIAD experiment at the Boulby Underground Laboratory
G. J. Alner et al., submitted to Phys. Lett. B (2005)
The DRIFT-II Dark Matter Detector: Design and Commissioning
G. J. Alner et al., submitted to Nuc. Instrum. Meth. A (2005)
Veto performance for large-scale xenon dark matter detectors
M.J.Carson et al., submitted to Nuc. Instrum. Meth. A (2004)
Muon-induced neutron production and detection with GEANT4 and FLUKA
H. M. Araujo et al., Astropart. Phys. (in press)
Neutron background in a large-scale xenon detector for dark matter searches.
M. J. Carson et al. Astropart. Phys. 21 (2004) 667-687
The DRIFT-I Dark Matter Detector at Boulby: design, installation and operation
G. J. Alner et al., Nucl. Instrum. and Meth. in Phys. Res. A 535(3) (2004) 644–655
Low energy alphas in the drift detector.
D. P. Snowden-Ifft et al., Nucl. Instrum. and Meth. in Phys. Res. A 516 (2004) 406–413
Reduction of Coincident Photomultiplier Noise Relevant to Astroparticle Physics Experiments.
M. Robinson et al., Astropart. Phys. (accepted )
Constraining SUSY dark matter with the ATLAS detector at the LHC,
G. Polesello and D. R. Tovey., JHEP 0405:071 (2004).
Studies of neutron shielding, calibration and veto systems for gaseous dark matter detectors.
P. F. Smith et al., Astroparticle Physics (in press)
Low-temperature study of 35 photomultiplier tubes for the ZEPLIN III experiment.
H. M. Araujo et al., Nucl. Instrum. and Meth. in Phys. Res. A 521 (2004) 407–415
Development of a gadolinium-loaded liquid scintillator for solar neutrino detection and neutron
measurements.
P. K. Lightfoot et al., Nucl. Instrum. and Meth. in Phys. Res. A 522 (2004) 439–446
First limits on nuclear recoil events from the ZEPLIN I Galactic Dark Matter Detector.
G. J. Alner et al.Astropart. Phys. (in press)
Reduction of Coincident Photomultiplier Noise Relevant to Astroparticle Physics Experiments.
M. Robinson et al. Astropart. Phys. (submitted and under review )
A Study of the Scintillation Induced by Alpha Particles and Gamma Rays in Liquid Xenon in an Electric
Field.
J. V. Dawson et al., Nucl. Instr, Meths., (in press)
Cold dark matter and the LHC,
D. R. Tovey et al., J, Phys. G (2004) in press
Direct detection of Dark Matter,
N.J.C. Spooner, SUSY04, Tokyo, 2004
Experimental progress in the Direct Detection of dark Matter,
N.J.T. Smith NAM2004 (Milton Keynes) 2004
Direct detection of Dark Matter,
N.J.C. Spooner, COSMO 2004, Toronto, 2004
The Boulby Dark Matter Programme.
S. M. Paling (on behalf of the Boulby Dark Matter Collaboration), 6th Int. Symp. Sources and Detection of
Dark Matter/Energy in the Universe (Marina del Rey, California, Feb 2004)
Simulation of neutron background for future large-scale particle dark matter detectors.
M. Robinson (for the UK Dark Matter Collaboration), 6th Int. Symp. Sources and Detection of Dark
Matter/Energy in the Universe (Marina del Rey, California, Feb 2004)
Results from the ZEPLIN I dark matter detector.
N.J.T.Smith (for the UK Dark Matter Collaboration), 6th Int. Symp. Sources and Detection of Dark
Matter/Energy in the Universe (Marina del Rey, California, Feb 2004)
ZEPLIN III: a liquid xenon dark matter detector
T.J.Sumner (for the UK Dark Matter Collaboration), 6th Int. Symp. Sources and Detection of Dark
Matter/Energy in the Universe (Marina del Rey, California, Feb 2004)
Dark Matter Searches at Boulby mine.
V. A. Kudryavtsev (for the Boulby Dark Matter Collaboration), XXXIXth Moriond Workshop (La Thuile,
Mar/Apr 2004)

PhDs awarded

ZEPLIN III: A Two-Phase Xenon WIMP Detector.
J. V. Dawson, Ph.D. Thesis (2003)
Development of a Two Phase Liquid Xenon Dark Matter Detector.
D. Davidge, Ph. D. Thesis (2004)
Dark Matter searches with Gas Time Projection Chambers.
B. Morgan, Ph. D. Thesis (2004)
Development of, and Analysis for, Xenon dark matter detectors.
R Holingworth, Ph. D. Thesis (2004)
Figure 1: The ZEPLIN I upper limit is the green curve.
Figure 2: Layout of the underground laboratory. The entire area is now a clean room of better
than class 2500. Stub A is class 1000 and is for instrument assembly and low-background
studies. The locations for ZEPLINs II and III and DRIFT II are shown. Layout of new Boulby
underground facilities.
Figure 3: Internal view of photomultiplier arrangement inside ZEPLIN II.
Figure 4: Assembled ZEPLIN II instrument.
Figure 5: ZEPLIN III internal view. The 31 photomultiplier arrangement can be seen at the top.
The liquid nitrogen reservoir is visible towards the bottom with its highly reflective multi-layer
insulation.
Figure 6: The first DRIFT II module undergoing surface commissioning
Figure 7: The first DRIFT II module in place in the underground laboratory.
Figure 1: The ZEPLIN I upper limit is the green curve.
Figure 2: Layout of the underground laboratory. The entire area is now a clean room of
better than class 2500. Stub A is class 1000 and is for instrument assembly and low-
background studies. The locations for ZEPLINs II and III and DRIFT II are shown.




Figure 3: Internal view of photomultiplier arrangement inside ZEPLIN II.
Figure 4: Assembled ZEPLIN II instrument.
Figure 5: ZEPLIN III internal view. The 31 photomultiplier arrangement can be seen at
the top. The liquid nitrogen reservoir is visible towards the bottom with its highly
reflective multi-layer insulation.




Figure 6: The first DRIFT II module undergoing surface commissioning
Figure 7: The first DRIFT II module in place in the underground laboratory.

				
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Description: DARK MATTER EXPERIMENTS