Direct Dark Matter Searches

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Direct Dark Matter Searches

• Véronique SANGLARD
• UCBL-CNRS/IN2P3/IPNL
• sanglard_at_ipnl.in2p3.fr

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Outline

• Motivations for non-baryonic dark matter search
• Principle of the direct detection
• Running experiments
• Future experiments
• Conclusion

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Motivations for Dark Matter Search (1)

• Rotation curves studies
• Dark matter halo around the galaxies
• Local density 0.3 GeV/cm3

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Motivations for Dark Matter Search (2)

• At cosmological scale
• Results of WMAP -gt
• O tot 1.00
• O baryon lt 0.05 (confirmed by experiments like
  EROS, MACHO)
• O matter 0.3
• O Cold Dark Matter 0.22
• Need weakly interacting non-baryonic massive
  particles
• WIMP (slt10-6 pb)

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Natural WIMP candidate

• Neutralino definition in the SUSY field
• Stable particle if R-parity
• conserved (LSP)

• Indirect detection
• Detection of WIMPs annihilation
• products

• Direct detection
• Detection of WIMPs scattering off
• nuclei

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Direct Search Principle

• Detection of the energy deposit due to elastic
  scattering on nuclei of detector in laboratory
  experiment
• Optimum sensitivity for MWIMP MRECOIL
• Rate lt 1 evt/day/kg of detector
• Need low background
• Deep underground sites
• Radio-purity of components
• Active/passive shielding
• Need large detector mass (kg -gt ton)
• Recoil energy 20 keV
• Need low recoil energy threshold

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WIMP signatures

• Nuclear recoils
• Not electron recoils (dominant background)
• Neutron scattering also produces recoils
• spectrum shape
• Exponential (as most bkg)
• Shape for backgrounds unknown/poorly predicted
• Coherent interaction (Spin-independent) ?
• Absence of multiple scattering (against neutron)
• Uniform rate throughout volume (against surface
  radioactivity)
• Directionality of nuclear recoils
• Annual rate modulation

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Direct detection techniques
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Current direct detection experiments
None
Statistical
Event-by-event
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NaI scintillation DAMA

• Based in Gran Sasso lab (3500 mwe)
• 100 kg of NaI(Tl)
• Exposure 107731 kg.d
• Coincidence between 2 PMTs
• Pulse shape rejection inefficient at 2 keVee
• Used annual modulation
• Claim annual modulation at 6.3s over 7 annual
  cycles
• M? 52 GeV/c²
• sn 7.2 10-6 pb
• Not compatible with CDMS, EDELWEISS experiments
• Future LIBRA (250 kg of NaI)

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NaI scintillation DAMA

• Based in Gran Sasso lab (3500 mwe)
• 100 kg of NaI(Tl)
• Exposure 107731 kg.d
• Coincidence between 2 PMTs
• Pulse shape rejection inefficient at 2 keVee
• Used annual modulation
• Claim annual modulation at 6.3s over 7 annual
  cycles
• M? 52 GeV/c²
• sn 7.2 10-6 pb
• Not compatible with CDMS, EDELWEISS experiments
• Future LIBRA (250 kg of NaI)

Single-hits events residual rates
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Ge ionization GENIUS-TF

• Based in Gran Sasso lab (3500 mwe)
• Running experiment
• 4x2.5 kg (up to 14) naked HPGe in N2
• Problems surface contamination by Radon
• Goal for background 1 count/(kg.keV.y)
  lt 50 keV
• But serious problems for GENIUS (1T of Ge in N2)

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Liquid Xe Scintillation ZEPLIN-I

• Based in Boulby mine (2800 mwe)
• 3.2 kg (fid.) -gt 230 kg.d
• Single phase
• 3 PMTs coincidence
• Pulse Shape Amplitude (time constant
  discrimination)
• Difficulties with neutron calibration at low
  energy (in deep site)
• Resolution 100 at 40 keV (7 keVee)
• Experiment now completed but no published results
  yet
• Future ZEPLIN II (30 kg)
  Ionizationscintillation

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Liquid Xe ScintillationIonization XENON

• Prototype 3kg (active mass) dual phase detector
  with TPCs
• 7 PMTs in the cold gas above the liquid
• Measurements of
• Primary scintillation light (S1)
• Secondary scintillation light from ionization
  electrons (S2)
• CsI photoelectron signal (S3)
• Discrimination variable S1/S2
• Current work
• Calibrations (?, a, neutrons)
• Future XENON10,100,1T in Gran Sasso lab

S1
S3
S2
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Liquid Xe ScintillationIonization XENON

• Prototype 3kg (active mass) dual phase detector
  with TPCs
• 7 PMTs in the cold gas above the liquid
• Measurements of
• Primary scintillation light (S1)
• Secondary scintillation light from ionization
  electrons (S2)
• CsI photoelectron signal (S3)
• Discrimination variable S1/S2
• Current work
• Calibrations (?, a, neutrons)
• Future XENON10,100,1T in Gran Sasso lab

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Phonon and scintillation/ionization bolometers

• Simultaneous measurement of phonon and
  scintillation/ionization
• Different (light or charge)/heat ratio for
  nuclear and electron recoils (WIMP and neutron
  have lower light/charge than ?s, ßs )
• Discrimination event-by-event of electron recoils
  (main background)

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Heat-scintillation CRESST-II

• Based in Gran Sasso lab (3500 mwe)
• 2x300g CaWO4 crystal W-SPT
• Net exposure 20.5 kg.d
• Rejection at 15 keV 99.7
• No neutron shield installed
• WIMP interact mainly with W
• Energy range 12-40 keV

separate cryogenic light detector
W SPT (W-Superconducting Transition Thermometers)
absorber
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Heat-scintillation CRESST-II
90 of nuclear recoils with quenching factor
Q7.4 below this line
90 of nuclear recoils with Q40 (W) below this
line 0 events (between 12 and 40 keV) Only
this detector used to derive exclusion limits
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Heat-ionization CDMS-II

• Based in Soudan Underground lab (2090
  mwe)
• 4x250g Ge 2x100g Si
• Net exposure 19.4 kg.d
• Detector ZIP (sensitive to athermal phonon)
• Active muon veto shielding (PE Pb)

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Heat-ionization CDMS-II

• Rejection of background surface events with
  timing cuts

0 events (between 10-100 keV)
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Heat-ionization EDELWEISS-I

• Based in Modane Underground laboratory (4800 mwe)
• Low radioactivity dilution cryostat at 17 mK
• Shielding PEPbCu
• 3x320g Ge
• Amorphous layer (Ge/Si)
• NTD Ge thermometric sensor
• Al electrode (one segmented)
• Fiducial volume 57
• Rejection-? 99.9 at 15 keV

3x320g heat-and-ionization Ge cryogenic detectors
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Heat-ionization EDELWEISS-I

• New data taking with trigger on phonon signal
• Improved efficiency at low energy (50 at 11
  keV)
• Fiducial exposure 22 kg.d
• Stable behavior over 4 months
• 18 nuclear recoil candidates gt 15 keV
• 1 n-n coincidence
• Possible backgrounds
• Residual neutron flux
• Miscollected charge events
• Not enough statistics to conclude

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Heat-ionization EDELWEISS-I

• Final results 62 kg.d (fid. exp.)
• 50 trigger efficiency at 15 keV
• 40 nuclear recoil candidates gt 15 keV
  (only 6 gt 30 keV)
• Unknown background
• Used method developed by S. Yellin to
  derive exclusion limits (as CDMS)
• No background subtraction
• New limits consistent with previous published
  results
• V.Sanglard et al. astro-ph/0503265 (to PRD)
• Experiment stopped in March 2004

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90 C.L. exclusion limits on WIMP-nucleon
scattering cross-section (spin-independent)
Only published results are reported
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Next step for running experiments

• CDMS-II
• 7 towers (4x250g Ge 2x100g Si)
• 2 running now
• CRESST-II
• 33x300g CaWO4
• Wiring to mK level
• New readout system
• Neutron shielding µ veto
• EDELWEISS-II
• Next slide

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EDELWEISS-II

• Low radioactivity cryostat with larger
  experimental volume (50 liters)
• Improved neutron shielding
• Addition of µ veto
• 1st phase 28 detectors (21x320g Ge7x400g
  NbSi)
• Up to 120 detectors
• Expected sensitivity 0.002
  evt/kg/day
• Installation in progress in LSM

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Conclusion

• Today 10-6 pb era
• Starting to test most optimistic SUSY models
• Next step 10-8 pb
• Increased detector mass
• Further reduce background rejection
• Lower energy threshold
• Improve event-by-event discrimination
• Goal 10-10 pb within 10 years
• Probe most of the allowed SUSY parameter space
• 1 ton scale (SuperCDMS, EURECA)
• Combined several targets

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Conclusion

• Today 10-6 pb era
• Starting to test most optimistic SUSY models
• Next step 10-8 pb
• Increased detector mass
• Further reduce background rejection
• Lower energy threshold
• Improve event-by-event discrimination
• Goal 10-10 pb within 10 years
• Probe most of the allowed SUSY parameter space
• 1 ton scale (SuperCDMS, EURECA)
• Combined several targets

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1 ton a simple experiment ?