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The European Future of Dark Matter Searches with Cryogenic Detectors
H KrausUniversity of Oxford
for the EURECA collaboration
EURECA
• Based on CRESST and EDELWEISS expertise, with additional groups joining.
• Target materials: Ge, CaWO4, etc (A dependence)
• Mass: above 100 kg towards 1 ton
• Timescale: after CRESST-II and EDELWEISS-II
• Started 17 March 2005 (meeting in Oxford)
• R&D: demonstrate CRESST / EDELWEISS
European Underground Rare Event
Calorimeter Array
United Kingdom
Oxford (H Kraus, coordinator)
Germany
MPI für Physik, Munich
Technische Universität München
Universität Tübingen
Universität Karlsruhe
Forschungszentrum Karlsruhe
Russia
DLNP Dubna
CRESST + EDELWEISS + new groups
EURECA Collaboration
France
CEA/DAPNIA Saclay
CEA/DRECAM Saclay
CNRS/CRTBT Grenoble
CNRS/CSNSM Orsay
CNRS/IPNL Lyon
CNRS/IAP Paris
CERN
Experiments – MSSM Predictions
σ = 10−6 pb:
~1 event/kg/day~0.1 now reached
σ = 10−8 pb:
~3 events/kg/yearAims of phase II experiments
σ = 10−10 pb:
~30 events/ton/yearNext generation requires further x100 improvement!
Dark Matter Signatures
1.Recoil energy spectrum Energy resolution exponential, similar to background.
2.Nuclear (not electron) recoils Discrimination is really required now.
3.Coherence: A dependence Multi-target essential once first signal is identified.
4.Absence of multiple interactions Large Array removes some fraction of background.
5.Diurnal modulation nice, but needs low-pressure gaseous target.
6.Annual modulation (requires many events) tricky; most events are close to threshold, small effect.
Detection Techniques
Ar, XeArDM, WARP, XENON, ZEPLIN
NaIDAMALIBRAANAISNAIAD
GeHDMSGenius-TFIGEXDRIFT
Si, GeCDMSEDELWEISS
Al2O3
CRESST I
CaWO4
CRESST IIROSEBUD
Cryogenic Techniques
Initial recoil energy
Displace-ments,
Vibrations
Athermalphonons
Ionization(~30 %)
Thermal phonons(Heat)
Scintillation
(~3 %)
Combination of phonon measurement with measurement of ionization or scintillation
Phonon: most precise total energy measurement
Ionization / Scintillation:
yield depends on recoiling particle
Nuclear / electron recoil discrimination.
EDELWEISS – Detectors
Target:
Cyl. Ge crystal, 320 gØ 70 mm, h = 20 mmPhonon - signal:
NTD-Ge (~ 20 mK)Ionisation - signal:
Inner disc / outer guard ring
Phonon – Ionisation
252Cf60Co
Excellent resolution in ionisation and phonon signals. Clean γ-calibration data: no event below Q = 0.7.
CRESST – Detectorsheat bath
thermal link
thermometer(W-film)
absorbercrystal
Particle interaction in absorber creates a temperature rise in thermometer which is proportional to energy deposition in absorber
Temperature pulse (~6keV)
Resis
tance [mΩ
]
normal-conducting
super-conducting
δδδδT
δδδδR
Width of transition: ~1mKSignals: few µ KStablity: ~ µ K
Phonon – ScintillationDiscrimination of nuclear recoils from radioactive backgrounds (electron recoils)
by simultaneous measurement of phonons and scintillation light
separate calorimeter as
light detector
light reflector
W-SPT
W-SPT
300 g CaWO4
proof of principle
En
erg
y i
n l
igh
t c
ha
nn
el
ke
Vee]
Energy in phonon channel [keV]
high rejection:99.7% > 15 keV99.9% > 20 keV
α – β/γ Discrimination
Danewich et al – Kiev(116CdWO4 – 330 g, 2975 hrs)
CRESST – LNGS(CaWO4 – 300 g, 633 hrs)
A ‘standard’ scintillator(pulse shape discrim.)
Scintillation part of a phonon – scintillation detector (CRESST)
α – β/γ Discrimination
Decay Identification
EURECA Strategy
Some aspects covered by ILIAS working groups.
Main thrust: demonstrate current experiments.
EDELWEISS: new (larger) cryostat; improved
shielding; 8kg Ge in 2006; reduction of surface events expected from improved radiopurity and/or use of NbSi sensors. Up to ~30kg target possible in cryostat.
CRESST: new (66 channel) SQUID readout system;
improved shielding; few kg CaWO4 in 2006; ongoing improvement of scintillation signals. Up to ~10kg target possible in present cryostat.
EURECA Tasks
Detector Development: improving rejection, target materials, optimizing size, mass production issues.
Readout and Electronics: scalability.
Cryogenic Environment: size, radiopurity, uptime.
Neutron and Muon Backgrounds: measurement, simulation and shielding design.
Extreme Low-background Materials: selection of materials, processing, handling, etc.
EDELWEISS II Ge / NTD Detectors
♦ Amorphous Ge and Si sub-layer: better charge collection for surface events
♦ Optimized NTD size and operating temp. (16-18 mK) : sub keV resolution
♦ New holder and connectors (Teflon and copper only)
Multi-target Approach
300 350 400 450 500 550 600 650 700 7500
5
10
15
20
25
Lu
min
esce
nce
in
tensity, a
.u.
Wavelength, nm
CaWO4
ZnWO4
CaMoO4
CdMoO4
MgMoO4
Excitation: 3.2keV Temperature: 8K
0 50 100 150 200 250 300 3500
20
40
60
80
100
120
CaWO4
ZnWO4
CdMoO4
CaMoO4In
ten
sity,
a.u
.Temperature, K
Germanium and Scintillators:
many materials scintillate…
Cryostat Designs
Cryo / Electronics InfastructureEDELWEISS: up to ~30kg
• Read out electronics:66 SQUIDs (CRESST), 100 high-impedance readout (EDELWEISS)
• Shielding / n-moderator / µ-veto:
Cu/Pb, 50 cm polyethylen, plastic scintillators, radon box, etc.
• Future cryogenic facility: Modular design, “hot-swap“, uptime, balance traditional with modern, address cabling (heat load) issue, separate: detector volume – cryostat, separate: cooling functions – readout
CRESST: up to ~10kg
The 66 channel SQUID readout system
• 66 chan. 33 detector modules with up to 10 kg of target material
• Will need 103 – 104
channels
• Need factor 5 – 10 denser packing
• More automatic tuning,
logging and control
Example:Electronics
EDELWEISS-II Electronics
♦ Electronics (by CEA and IN2P3) directly on the cryostat
♦ Heat modulation and charge bias by programmable DACs
♦ Continuous 200 kHz digitization, output by optical fibers
♦ Filtering, demodulation and trigger by soft in the acquisition system
Numeric
(DACs and
ADCs
Heat
amplifier
Charge
amplifiers
Power supply
To the cryostat
(cold electronics and
bolometers)
Outputs
EURECA Near Future
• R&D through EDELWEISS and CRESST.
• ILIAS working groups.
• EU – FP7 Design Study for Detector Module Layout, Shielding, Underground Infrastructure, etc.
• Apply to national funding agencies.
• Building on EDELWEISS and CRESST expertise to build tonne-scale cryogenic experiment.
Summary
CRESST and EDELWEISS on track; improvements w.r.t. present achievements will have to be shown.
Cryogenic Detector Technology with nuclear recoil identification has the potential required for these improvements.
EURECA builds on CRESST and EDELWEISS expertise aiming towards a European multi-target array for direct dark matter searches.