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UKDMC, measured for DM77. Xe Target lined with PTFE reflector. recoil discrimination. Xe filled Turrets capped by quartz windows. DAMA, preprint INFN/AE-00/10, 2000. 3 modules. gammas. 4 sub- units. CS 2. C recoils. - PowerPoint PPT Presentation
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Dark Matter Experiments at Boulby mine The Boulby Dark Matter Collaboration
Imperial College of Science, Technology and Medicine, London: B. Ahmed, A. Bewick, D. Davidge, J. V. Dawson, A. S. Howard, W. G. Jones, M. K. Joshi, V. Lebedenko, I. Liubarsky, R. LЯscher, T. J. Sumner, J. J. Quenby; Rutherford Appleton Laboratory: G. J. Alner, S. P. Hart, I. Ivaniouchenkov, J. D. Lewin, R. M. Preece, N. J. T. Smith, P.F. Smith; Queen Mary, University of London: J. C. Barton;
University of Sheffield: M. J. Carson, T. Gamble, R. Hollingworth, V. A. Kudryavtsev, T. B. Lawson, P. K. Lightfoot, J. E. McMillan, B. Morgan, G. Nicklin, S. M. Paling, J. W. Roberts, M. Robinson, N. J. C. Spooner, D R. Tovey; Occidental College: D. P. Snowden-Ifft, J. Kirkpatrick; Temple University: C. J. Martoff, R. Ayad; UCLA: D. B. Cline, H. Wang, Y. Seo, M. Atac, F. Sergiampietri; LLNL: W. W. Craig;
Columbia University: C. J. Hailey, M. Sileo, P. Graham, J. Hong; CERN/ICGF-CNR-Torino/INFN-Padova: P. Picchi, F. Pietropaolo, L. Periale, G. Mannocchi, C. Castagnoli; ITEP, Moscow: D. Akimov, A. Danilov; Texas A&M University: J. T. White, J. Gao; UMSNH, Morelia, Mexico: U. Cotti, M. Reyes, L. Villasenor; CINVESTAV, Mexico City: A. Zepeda
NAIAD - NaI Advanced Detector ZEPLIN - ZonEd Proportional scintillation in LIquid Noble gases
DRIFT - Directional Recoil Identification from TracksMotivation:
• Two different targets with high and low masses• Sensitive to both spin-independent and spin-dependent WIMP-nucleus interactions• Aimed to confirm or refute annual modulation signal, claimed by DAMA, with similar type detectors (NaI) but different analysis technique• Can be also used as a diagnostic array to study backgrounds and systematic effects for other dark matter experiments at Boulby
«NAIAD» by John William Waterhouse
Signal discrimination:• Pulse Shape Analysis is used to discriminate between nuclear recoils, which can be caused by WIMP interactions, and electron recoils due to gamma background• Light yield determines the discrimination power of the pulse shape analysis• Running unencapsulated crystals requires stability of the light yield• Each crystal is calibrated with gamma and neutron sources• Integrated pulses are fitted to an exponential• Time constant distributions are fitted to the log(Gauss) function (or two log(Gauss) functions in case of two components) + PMT noise• In real data we search for the second (fast) component with known parameters
gammasource
neutronsource
electronrecoils fromgammabackground
nuclearrecoils
Compton calibrationwith gamma source - electron recoils
Data shows one population of scintillation pulses + PMT noise
6-7 keV 7-8 keV
UKDMC, measuredfor DM77
Sakai, IEEE Transactions on Nuclear Science, vol. NS-34, 1987 - 1 cm crystal
DAMA, preprint INFN/AE-00/10, 2000
Energy calibration and energy resolution
NAIAD results• 6 crystals are currently running at Boulby. Data from 4 crystals have been analysed to set new limits on WIMP-nucleon spin-independent interactions; total exposure = 10.6 kg x years.• Significant improvement over previous limits (1996) has been achieved due to higher light yield and better discrimination.• Extensive studies of NaI(Tl) crystals and their response to various radiations have been performed (energy calibration and resolution, gamma and neutron calibrations etc.).• Pulse shape analysis has been proven to work in NaI detectors and to produce reliable limits. DAMA can use PSA to confirm or refute the positive signal found in annual modulation analysis.
1 ton liquid PXE scintillator Veto
Xe Target lined with PTFE reflector
Xe filled Turretscapped by quartz windows
3.7kg liquid Xe
Xe lineCoolant line
PhotomultiplierVacuum pump oninsulation jacket T90 / ns
Boulby underground laboratory - 1100 metres underground in the salt and potash mine
0
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0 10 20 30 40
observed energy keV
neutron/gamma TC ratio
Fits
t(exp)t(70%)t(av90%)
Calibrations with :• Various gamma sources• Am-Be neutron/gamma sourceVarious measurements of pulse shape• Fitted exponential, t• Mean photon arrival time, T90 • Time to reach 70%, T70
Distributed as a gamma function in 1/X
ZEPLIN I - Liquid XeSinglet/triplet ratio differs for nuclear and electron recoilsRecombination is relevant only for electron recoils (=> t~45ns)Pulse Shape Analysis is applied
Noise cuts (asymmetry cuts, fiducial volume cuts) are applied using projection of normalised amplitude from each PMT onto a plane - S3 cut
Background rejection by Compton veto (liquid scintillator) and S3 cut
0.00001
0.0001
0.001
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0.1
1 10 100
fitted time constant ns
data
gamma cal
GD fit
0.00001
0.0001
0.001
0.01
0.1
1 10 100
fitted time constant ns
c2
Poisson
• 27 days of live time = 90 kg x days• gamma calibration data from contemporaneous veto events• Gamma function fit to 1/ t distribution• Analysis: c2 in high statistics region, Poisson in tail
Spin-independent pb limits for ZEPLIN I, showing other world limits and DAMA signal region
0.000001
0.00001
0.0001
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1 10 100 1000 10000
Mass GeV
ZEPLIN I (25 d)ZEPLIN I (est 8m)EdelWeissCDMSIGEXDAMA (ann mod)
ZEPLIN II - Double Phase Xe Detector - under construction (30 kg)
Xe detector with field:• Electric field prevents recombination and allows the measurement of the ionisation yield.• For electron recoils the track is less dense and the electric field is more efficient in separating electrons from ions.• Ionisation electron drifts towards a high field region in the gas phase.• Electro-luminescence light from the avalanche process around a multi-wire plane is detected as 2nd scintillation.
Active volume
Gas phase
g
Electro-luminescence
Primary-Scintillation
nuclear recoils: high primary scintillation, low ionisation yield (2nd scintillation)electron recoils: low primary scintillation, high ionisation yield (2nd scintillation)
3 modules
80 kg target
4 sub- units
shielding
ZEPLIN III and ZEPLIN MAX - Double Phase Xe Detector withhigh electric field - at R&D phase
• alpha population gradually moves closer to vertical as the E-field is increased
• Primary vs secondary scintillation for alphas for several values of electric field
The effect of increasing the voltage from 7kV to 12kV
Towards 1 ton Xe detectorZEPLIN MAX
Poster made by V. A. Kudryavtsev, University of Sheffield, UKE-mail: [email protected], http://www.shef.ac.uk/~phys/people/vitaly/
UKDMC web-site: http:// hepwww.rl.ac.uk/ukdmc/
New Caverns at Boulby50 m
New surface lab
Directionality:• WIMP velocity distribution in the Earth’s frame is strongly peaked in the direction of the solar motion – A WIMP ‘wind’• A strong signature - sidereal variation of the directions of recoil tracks• Distribution of recoil directions in galactic coordinates is peaked in direction opposite to solar motion
DRIFT concept -low pressure (40 torr) gas Time Projection Chamber• Ionisation tracks > 1 mm.• Electrons are drifted in an electric field to the x-y readout region.• Drift time measurements provide z-co-ordinates of the tracks.• This allows full 3D reconstruction of events (track length, energy, orientation)
Simulation of tracks from different particles in a low pressure gas
Negative ion DRIFT:electron capture by electronegative gas reduces track diffusion (~0.5 mm at 0.5 m drift length)
Electric Field
Scattered WIMP
MWPC Readout
Plane
Cathode
Drift direction
CSCS22
Recoil Atom
DRIFT I - first directional WIMP detector
DRIFT I at Boulby
Large scale DRIFT design
High resolution readout
WIM
P-n
ucle
on
cro
ss-s
ecti
on
, p
b NaI 1996
NAIAD/Xe 2002/3
Xe 2003/4
DRIFT 2004/5
Xe 2005
Xe-MAX 2006
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10 100 1000WIMP mass, GeV
ZEPLIN II
DRIFT II and DRIFT III - towards a 100 kg directional detector
Vacuum Vessel Optics Modules
Projected sensitivity of WIMP detectors at Boulby
Preliminary limits from ZEPLIN I
ZEPLIN I: results
Response of a prototype detector to gammas and neutrons
C recoils
S recoils
gammas
recoil discrimination