The ZEPLIN II Liquid Xenon Dark Matter Detector

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The ZEPLIN II Liquid Xenon Dark Matter Detector

• Hanguo Wang,
• UCLA, Physics and Astronomy
• Dec. 8, 2002 Caltech Tues. Seminar

Zoned Electro-luminescence and Primary Light In
Noble-gases

• Why Xenon
• Detailed properties of Xe
• ZEPLIN I Result (underground operation)
• The ZEPLIN II Detector
• Current Future RD plan
• Specific Site Requirement

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The ZEPLIN II Collaboration
DB Cline, M Atac, Y Seo, F Sergiampietri(a), H
Wang Physics and Astronomy, UCLA , (a) Pisa JT
White, J Gao Department of Physics, Texas AM
University P Picchi, L Periale, G Mannocchi, F
Pietropaolo ICGF-CNR-Torino/INFN-Padova GJ
Alner, SP Hart, JD Lewin, RM Preece, JW Roberts,
NJT Smith, PF Smith Particle Physics Department,
Rutherford Appleton Laboratory, Chilton, Oxon B
Ahmed, A Bewick, D Davidge, JV Dawson, AS Howard,
I Ivaniouchenkov, WG Jones, MK Joshi, V
Lebedenko, I Liubarsky, R Lüscher, T J Sumner, J
J Quenby Blackett Laboratory, Imperial College
of Science, Technology and Medicine, London MJ
Carson, T Gamble, VA Kudryavtsev, TB Lawson, MJ
Lehner, PK Lightfoot, JE McMillan, B Morgan, SM
Pealing, M Robinson, NJC Spooner, DR
Tovey Department of Physics and Astronomy,
University of Sheffield
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Direct Detection
WIMPs
M?
MN
Sun motion 230km/s
R event rate per unit mass 0.10.001events/kg/day
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Detector response to WIMPs and Background
(I, S, Th)
Background Discrimination
(I,S,Th)
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Why Xenon

• Available in Large Quantities
• Large abundance for both s½ (129Xe26) and s0
  (132Xe27)
• High Atomic Number (ZXe54, ?WIMP-Nucleon ? A2)
• High Density ( 3g/cm3 liquid) (compact detector
  design)
• High Scintillation Light (175nm) Ionization
  Yield
• Small fano factor ( F
  0.041 Energy Resolution
  )
• Scintillation decay profile difference (primary)
  (PSD)
• Large quenching factor (observed
  energy/e.e.Energy)
• Can be Highly Purified
• long light attenuation length (m)
• long free electron life time (5ms)
• Gamma Recoil signal Discrimination
• Capable of Scale up to Large Volume (ton)
• No Long Lived Radioactive Isotopes (low
  background)

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Xenon Isotopes Natural Abundance
Mostly odd
Mostly even
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Liquid Xenon Scintillation Mechanism

• Pulse Shape discrimination
• due to decay profile difference between
  nuclear recoil electron recoil
• (B) When Edrift applied, and measure Ei Es,
• Very good background rejection due to
  (Ei/Es)M.I.P.gtgt (Ei/Es)H.I.P.
• ZEPLIN I (A)
• ZEPLIN II (AB)

Edrift
Nuclear recoil Electron recoil
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ZEPLIN I underground installation
1990s
ZEPLIN I Veto
2000
2002
Actual xenon target
Target chamber
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Pulse Shape Discrimination and ZEPLIN I Results
Middlesborough
Staithes
Whitby
York
Boulby Site 1,100-m deep underground
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Depth (mwe) WIPP 1600-2300
Soudan 2200 Boulby 3300 Gran Sasso
3800 Sudbury 6200 San Jacinto 5400-6300
Homestake 7200
Boulby mine
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Pulse Shape DiscriminationZEPLIN I Results
(UKDMC, N.J.T.Smith, IDM2002, York)

• Using different fitting techniques
• Exp, Mean, mean to90, median
• Fitted gamma density function in 1/t
• Lab calibrations data to 7keV
• Surface ambient neutrons to 4 keV

Gamma source
Neutron source
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ZEPLIN I Gold Data Run(UKDMC, N.J.T.Smith,
IDM2002, York)

• 75 day live-time, 230kg.days data
• Gamma calibration data from contemporaneous veto
  events
• Gamma density fit (actually in 1/t) as guide
  smooth slope
• Analysis ML over signal region (tbd), poisson on
  tail

c2
Poisson
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ZEPLIN I RESULTS (UKDMC, N.J.T.Smith, IDM2002,
York)

• Based on lab neutron
• discrimination
• (source and ambient)
• To be re-done underground
• Efficiencies incorporated
• Poisson trigger efficiency
• (analytically)
• Light collection response
• matrix
• S3 volume efficiency cut
• Dead-time
• Standard DM model
• Nuclear physics
• Quenching
• Form factor

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ZEPLIN I
Operating at Boulby Mine and already reach Below
DAMA (UKDMC, N.J.T.Smith, IDM2002, York)
ZEPLIN I target in liquid scintillator veto
Veto and Detector
Shield and Veto
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Liquid Xenon Scintillation Mechanism

• Pulse Shape discrimination
• due to decay profile difference between
  nuclear recoil electron recoil
• (B) When Edrift applied, and measure Ei Es,
• Very good background rejection due to
  (Ei/Es)M.I.P.gtgt (Ei/Es)H.I.P.
• ZEPLIN I (A)
• ZEPLIN II (AB)

Edrift
Nuclear recoil Electron recoil
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Principle Tests Setup
NIM A327 (1993) 203

• Ceramic.
• Quartz Window,
• Stainless Steel Cathode.
• 4. Source.
• 5. Grounded Grid.
• 6. Anode wire frame

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Electron lifetime and drift velocity in LXe
Under 10V/cm drift field e-life-time gt 5ms
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Xenon Two-Phase Prototype Detector
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Xenon Two-Phase Prototype Detector
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Xenon Two-Phase Prototype Detector
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Xenon Two-Phase Prototype Detector
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Xenon Two-Phase Prototype Detector
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ZEPLIN IICrossSection View
HV, Signal Feed-through
Cold Head
Copper Cast
Accessory Ports
Stainless Steel Cast
Vacuum
Thin Mesh Frame
Gas Xenon
PMT
Field Ring
Liquid Xenon
PTFE
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ZEPLIN II Detector
cut-away view of ZEPLIN II
Cold Head
Target vessel Oxygen Free Copper Cast
PMT
Liquid Xenon
PTFE
Vacuum vessel Stainless Steel Cast
Rendered by Roy Preece (RAL)
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ZEPLIN II Drawing Details
Inlet assembly showing all in-out ports for HV,
vacuum, xenon gas, thermal Sensors, And
cooling Head
Details showing field shaping rings, PTFE cone,
PTFE tube, bottom HV plate, Mesh frames, PMTs,
target vessel, and Vacuum vessel.
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Details of ZEPLIN II
HV

• Fiducially volume 30kg.
• Two fine-meshes provide both
• electron extraction field
• Electro-luminescence field
• Pure copper rings shapes the electron drift-field
  in liquid.
• -HV applies to bottom plate to have high field
  for ionization electron extraction in liquid.
• Extreme care taken to avoid HV discharge in gas.
• Seven custom made PMTs for use in liquid xenon
  temperature
• Custom made resister-dividers for PMTs for use in
  gas xenon.
• Dead region less than 0.1

PMTs
Mesh Frame
PTFE
HV Plate
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ZEPLIN II with Veto setup
Render by R Preece (RAL)
Final setup to be placed in lead shield
Liquid Scintillator Veto
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ZEPLIN II system Setup

• Cooling and Feed-Through
• Stainless Steel Cast Vacuum Vessel
• Copper Cast Target Vessel
• The Central Detector
• Active Veto
• Liquid Xenon Target
• Lead Shield

PMT
PMT
PMT
Liquid Scintillator
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Construction in Progress
Top view
The largest PTFE piece is being machined at the
UCLA Physics department machine shop
Vacuum and target vessel joining collar From a
solid steel
Bottom view
rings
cone
Field shaping rings are made out of pure Oxygen
free copper
Insulation tube
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Stainless Steel cast Vacuum Vessel
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Machining in Progress
Stainless Steel Cast
Top
bottom
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One Ton Scale-up based on the ZEPLIN II Design
Signal cable, HV cable, Cooling system, Vacuum,
and xenon port

• Total mass one ton and up
• 80 5-inch PMTs, or new devices (RD)
• Oxygen Free Copper Cast Vessel,
• for low background
• Signal amplification using CsI internal
  photo-cathode and/or other method (RD)
• Active neutron veto
• Gd loaded scintillation veto to remove
  neutrons from both inside and outside of detector
  
• Detector material samples are being tested for
  U Th contamination
• and Possible Gd loading in PTFE are under study
  for neutron veto

Muon veto is need for neutron background Below
10-8 pb sensitivity _at_Boulby Full MC simulation
will be done soon
The goal of ZELIN II operation and RD
Ton scale detector
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Theoretical predictions
ZEPLIN II
ZEPLIN IV
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Conclusion

• High A number makes it match better the high
  mass WIMPs and yields high event rates. (? ? ?2)
• High scintillation and ionization yield makes it
  easy to achieve the following
• Low energy threshold less than 10keV (true
  recoil energy). (good light collection eff.)
• good energy resolution (small Fano factor)
• Gamma and nuclear recoil discrimination by a
  factor of 1000.
• High liquid temperature and high density allows
  compact design and easy engineering solutions.
• Construction well underway.
• Supported by DOE during RD and construction and
  will continue to support operation
• 4 years NSF support for the ZEPLIN II operation,
  and ZEPLIN IV RD.
• ZEPLIN I already covered the DAMA region with
  230kg.days data (NJT smith, IDM2002).
• ZEPIN II will do well below DAMA (with both PSD
  and Ionizationscintillation)
• new ideas and RD still under way for large
  scale ZEPLIN IV to cover SUSY region.

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Specific Infrastructure Requirements Underground
Basics Requirement Depth Space 4x6x3 Power
few KW peak Heating Electric Cooling LN2 and
Compressor
Special Facilities Water Purification De-ionized
water Laser Optics No Vibration Control
No Cryogenics LN2 Radioactive Source Yes
Background Tolerance Muons Global Muon
veto? Ambient Gamma Rays Neutrons ? Radon ?
Fabrication Processes Machine Shop Yes Clean
Room Yes Electroforming ? Material Storage
Yes Chemical Etching Yes
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Activity Schedule
Two to six people with 24/7 access during RD and
installation Two to four people with 24/7 access
during operation phase The operation is planned
mainly by remote controls (at surface). The
schedule will depends on the current experiment
result at Boulby with the ZEPLIN II detector.
If Muon and neutron background proves to be
problem, the earliest plan will be Mid 2004.