Transcript Direct Dark Matter Searches

Direct Dark Matter
Searches
Véronique SANGLARD
UCBL-CNRS/IN2P3/IPNL
[email protected]
Outline
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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)
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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 ->
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Ω tot ~ 1.00
Ω baryon < 0.05 (confirmed
by experiments like EROS,
MACHO)
Ω matter ~ 0.3
Ω Cold Dark Matter ~ 0.22
Need weakly interacting
non-baryonic massive
particles …
WIMP (σ<10-6 pb)
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Natural WIMP candidate
     Z   H   H
0
1
 Neutralino definition in the
0
2 SUSY field
 Stable particle if R-parity
conserved (LSP)
 Indirect detection :
 Detection of WIMPs annihilation
products
 Direct detection :
 Detection of WIMPs scattering off
nuclei
DAMA
SUPER K
EDELWEISS
AMANDA
ANTARES
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CDMS
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Direct Search Principle
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Detection of the energy deposit due to elastic scattering on nuclei of
detector in laboratory experiment
Optimum sensitivity for MWIMP ~ MRECOIL
Rate < 1 evt/day/kg of detector
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Need low background
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Deep underground sites
Radio-purity of components
Active/passive shielding
Need large detector mass (kg -> ton)
Recoil energy ~ 20 keV
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Need low recoil energy threshold
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WIMP signatures
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Nuclear recoils
Not electron recoils (dominant background)
 Neutron scattering also produces recoils …
dN
spectrum shape
dE recoil
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Exponential (as most bkg)
Shape for backgrounds : unknown/poorly predicted
2 2
Coherent interaction (Spin-independent) ?  A   A
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
WIMP
Elastic nuclear scattering
Ge
10% energy
Ge, Si
Ionization
Liquid Xe
Target
Heat
Al2O3, LiF
100% energy
slowest
cryogenics
Light
NaI, Xe
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1% energy
fastest
no surface effects
CaWO4, BGO
WIMP
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Current direct detection experiments
Discrimination
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Name
Location
Technique
Material
Status
CUORICINO
Gran Sasso
Heat
41 kg TeO2
running
GENIUS-TF
Gran Sasso
Ionization
10 to 40 kg Ge in N2
running ???
HDMS
Gran Sasso
Ionization
0.2 kg Ge diodes
stopped
IGEX
Canfranc
Ionization
2 kg Ge Diodes
stopped
DAMA
Gran Sasso
Light
100 kg NaI
stopped
LIBRA
Gran Sasso
Light
250 kg NaI
running
NaIAD
Boulby mine
Light
46 kg NaI
stopped
ZEPLIN-I
Boulby mine
Light
4 kg Liquid Xe
stopped
XENON
Surface to GS
Light+ Ionization
3 to 10 kg Liquid Xe
running
ZEPLIN II
Boulby mine
Light+ Ionization
6 kg Liquid Xe
running
CDMS-I
Stanford
Heat + Ionization
1 Kg Ge + 0.2 Kg Si
stopped
CDMS-II
Soudan mine
Heat + Ionization
2 to 7 kg Ge + 0.4 to 1.4 Kg Si
running
CRESST-I
Gran Sasso
Heat + Light
0.262 kg Al2O3
stopped
CRESST-II
Gran Sasso
Heat + Light
0.6 to 9.9 kg CaWO4
running
EDELWEISS-I
Modane
Heat + Ionization
1 kg Ge
stopped
EDELWEISS-II
Modane
Heat + Ionization
10 to 30 kg Ge
In istallation
PICASSO
SNO
Bubble chamber
20 g Freon
running
ROSEBUD
Canfranc
Heat + Light
50 g Al2O3 + 67 g Ge + 54 g
CaWO4
running
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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 6.3σ over
7 annual cycles
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NaI
NaI
NaI
NaI
PMT
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PMT
NaI scintillation : DAMA
Mχ ~ 52 GeV/c²
σn ~ 7.2 10-6 pb
Not compatible with CDMS,
EDELWEISS experiments
Future = LIBRA (250 kg of NaI)
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NaI scintillation : DAMA
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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 6.3σ over
7 annual cycles
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Mχ ~ 52 GeV/c²
σn ~ 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
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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) < 50 keV
But serious problems for
GENIUS (1T of Ge in N2)
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Liquid Xe Scintillation : ZEPLIN-I
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Based in Boulby mine
Xe+
(2800 mwe)
Ionization
+Xe
3.2 kg (fid.) -> 230 kg.d
Electron/nuclear recoil
Xe2+
Single phase
Excitation
3 PMTs coincidence
+e(recombination)
Pulse Shape Amplitude (time
Xe*
Xe** + Xe
constant discrimination)
+Xe
Difficulties with neutron
calibration at low energy
Xe2*
175nm
175nm
(in deep site)
Singlet
Triplet
Resolution 100% at 40 keV
3ns
27ns
(7 keVee)
2Xe
2Xe
Experiment now completed but no
published results yet
Future : ZEPLIN II (30 kg)
Ionization+scintillation
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Liquid Xe Scintillation+Ionization :
XENON
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Prototype 3kg (active mass) dual
phase detector with TPCs
7 PMTs in the cold gas
above
the liquid
Measurements of
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Discrimination variable S1/S2
Current work
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Primary scintillation light (S1)
Secondary scintillation light from
ionization electrons (S2)
CsI photoelectron signal (S3)
S1
S2
S3
Calibrations (γ, α, neutrons)
Future : XENON10,100,1T in Gran
Sasso lab
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Liquid Xe Scintillation+Ionization :
XENON
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Prototype 3kg (active mass) dual
phase detector with TPCs
7 PMTs in the cold gas
above
the liquid
Measurements of
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Discrimination variable S1/S2
Current work
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Primary scintillation light (S1)
Secondary scintillation light from
ionization electrons (S2)
CsI photoelectron signal (S3)
Calibrations (γ, α, neutrons)
Electronic recoils
First plot
showing
neutron
calibration with
Liquid Xe
Nuclear recoils
Simulation of
detector
response
for neutron
calibration
Future : XENON10,100,1T in Gran
Sasso lab
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Phonon and scintillation/ionization
bolometers
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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 γs, βs )
Discrimination event-byevent of electron recoils
(main background)
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Heat-scintillation : CRESST-II
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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
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separate cryogenic
light detector
W SPT
(W-Superconducting
Transition Thermometers)
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Heat-scintillation: CRESST-II
90% of nuclear recoils
with quenching factor
Q=7.4 below this line
90% of nuclear recoils
with Q=40 (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
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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)
FET cards
SQUID cards
4K
P honon D
SQUID array
R bias
R feedb ack
I bias
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D
A
C
B
Q outer
Q inner
Vqbias
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0.6 K
0.06 K
0.02 K
ZIP 1 (Ge)
ZIP 2 (Ge)
ZIP 3 (Ge)
ZIP 4 (Si)
ZIP 5 (Ge)
ZIP 6 (Si)
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Heat-ionization: CDMS-II
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Rejection of background surface events with timing cuts
0 events
(between 10-100 keV)
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Heat-ionization: EDELWEISS-I
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Based in Modane Underground
laboratory (4800 mwe)
Low radioactivity dilution cryostat
at 17 mK
Shielding : PE+Pb+Cu
3x320g Ge
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Amorphous layer (Ge/Si)
NTD Ge thermometric sensor
Al electrode (one segmented)
Fiducial volume: 57%
Rejection-γ 99.9% at 15 keV
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3x320g heat-and-ionization
Ge cryogenic detectors
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Heat-ionization: EDELWEISS-I
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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
> 15 keV
1 n-n coincidence
Possible backgrounds
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Residual neutron flux
Miscollected charge events
Not enough statistics to
conclude
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Heat-ionization: EDELWEISS-I
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Final results: 62 kg.d (fid. exp.)
50% trigger efficiency at 15 keV
40 nuclear recoil candidates > 15 keV
(only 6 > 30 keV)
Unknown background
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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
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CDMS-II
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CRESST-II
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7 towers (=4x250g Ge + 2x100g Si)
2 running now
33x300g CaWO4
Wiring to mK level
New readout system
Neutron shielding + μ veto
EDELWEISS-II
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EDELWEISS-II
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Low radioactivity cryostat with
larger experimental volume
(50 liters)
Improved neutron shielding
Addition of μ veto
1st phase: 28 detectors
(21x320g Ge+7x400g NbSi)
Up to 120 detectors
Expected sensitivity:
0.002 evt/kg/day
Installation in progress in LSM
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Conclusion
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Today: 10-6 pb era
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Next step: 10-8 pb
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Starting to test most optimistic
SUSY models
Increased detector mass
Further reduce background
rejection
Lower energy threshold
Improve event-by-event
discrimination
Goal: 10-10 pb within 10 years
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Probe most of the allowed
SUSY parameter space
1 ton scale (SuperCDMS,
EURECA)
Combined several targets
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Conclusion
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Today: 10-6 pb era
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Next step: 10-8 pb
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Starting to test most optimistic
SUSY models
Increased detector mass
Further reduce background
rejection
Lower energy threshold
Improve event-by-event
discrimination
Goal: 10-10 pb within 10 years
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V. SANGLARD
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 ?
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