Transcript Dark Matter Experiments at Boulby mine The Boulby Dark Matter

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
Motivation:
• 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
DRIFT - Directional Recoil
Identification from Tracks
50 m
Boulby underground laboratory - 1100
metres underground in the salt and
potash mine
New Caverns at Boulby
«NAIAD» by John William Waterhouse
New surface lab
Xe filled Turrets
capped by quartz windows
ZEPLIN I - Liquid Xe
Directionality:
Singlet/triplet ratio differs for nuclear and
electron recoils
Recombination is relevant only for
electron recoils (=> t~45ns)
Pulse Shape Analysis is applied
Xe Target lined with PTFE reflector
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
•
3.7kg liquid
Xe
Calibrations with :
• Various gamma sources
• Am-Be neutron/gamma source
Various 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
1 ton liquid PXE scintillator Veto
Coolant line
Signal discrimination:
Xe line
• 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
DRIFT concept -low pressure
(40 torr) gas Time Projection
Chamber
1
neutron/gamma TC ratio
0.9
Photomultiplier
0.8
0.7
Fits
t(av90%)
t(70%)
t(exp)
0.6
0.5
0.4
0.3
0.2
0.1
Vacuum pump on
insulation jacket
0
0
10
20
30
40
T90 / ns
observed energy keV
Noise cuts (asymmetry cuts, fiducial
volume cuts) are applied using
projection of normalised amplitude
from each PMT onto a plane - S3 cut
gamma
source
neutron
source
Scattered
WIMP
electron
recoils from
gamma
background
Recoil
Atom
Drift direction
Cathode
Simulation of tracks
from different particles
in a low pressure gas
DRIFT I - first directional WIMP detector
ZEPLIN I: results
0.1
• 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
0.1
c2
data
0.01
0.01
gamma cal
GD fit
7-8 keV
0.001
0.001
Poisson
Compton calibration
with gamma source electron recoils
0.0001
0.0001
0.00001
0.00001
1
10
100
1
fitted time constant ns
10
100
fitted time constant ns
Preliminary limits from ZEPLIN I
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.
Data shows one
population of scintillation
pulses + PMT noise
Energy calibration and energy resolution
UKDMC, measured
for DM77
DAMA, preprint
INFN/AE-00/10, 2000
MWPC
Readout
Plane
Electric
Field
Negative ion DRIFT:
electron capture by
electronegative gas
reduces track diffusion
(~0.5 mm at 0.5 m drift
length)
Background rejection by
Compton veto (liquid
scintillator) and S3 cut
nuclear
recoils
6-7 keV
• 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)
CS2
DRIFT I at Boulby
Response of a
prototype
detector to
gammas and
neutrons
recoil discrimination
DRIFT II and DRIFT III
- towards a 100 kg
directional detector
gammas
ZEPLIN II - Double Phase Xe Detector - under
C recoils
construction (30 kg)
S recoils
Sakai, IEEE
Transactions on Nuclear
Science, vol. NS-34,
1987 - 1 cm crystal
Electroluminescence
Gas
phase
nuclear recoils: high primary scintillation,
low ionisation yield
(2nd scintillation)
electron recoils: low primary scintillation,
high ionisation yield
(2nd scintillation)
Vacuum
Vessel
High
resolution
readout
Optics Modules
Large scale DRIFT design
Active
volume
g
PrimaryScintillation
ZEPLIN III and ZEPLIN MAX Double Phase Xe Detector with
high electric field - at R&D phase
Projected sensitivity of WIMP detectors at Boulby
10-3
NaI 1996
10-4
The effect of increasing the voltage from 7kV to 12kV
3 modules
4 sub- units
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.
10-5
NAIAD/Xe 2002/3
10-6
Xe 2003/4
10-7
DRIFT 2004/5
10-8
Xe 2005
Xe-MAX 2006
10-9
10-10
shielding
80 kg target
10
100
1000
WIMP mass, GeV
• Primary vs secondary scintillation for alphas for
several values of electric field
ZEPLIN II
• alpha population gradually moves closer to
vertical as the E-field is increased
Towards 1 ton Xe detector
ZEPLIN MAX
Poster made by V. A. Kudryavtsev, University of Sheffield, UK
E-mail: [email protected], http://www.shef.ac.uk/~phys/people/vitaly/
UKDMC web-site: http:// hepwww.rl.ac.uk/ukdmc/