Edelweiss-II : status and first results
A new generation of background-free bolometers for WIMP search
X-F. Navick - CEA Saclay, IRFU, France
LTD13 – Stanford July 24th 2009
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Direct search for WIMPs with cryogenic detectors
astro-ph/08054705
KIMS
EDELWEISS-I
CRESST-II
CDMS-IIXENON
WIMPs forming our Galactic halo• 10 - 1000 GeV mass• v ~ 200 km/s ⇒ 0-50 keV nuclear recoils
(~ exponential spectrum)
SUSY neutralino (σ prediction)• <1 collision / kg / month
Cryogenic 10mK phonon/ionization detectors :
Detector requirements on both channelslow thresholdsexcellent discrimination between populationsbackground and signal identification
Xe
Ge
Navick - LTD13 - Stanford - July 09
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Phonon-ionization « NTD » sensors type
Edelweiss-I detectors Ionization measurement @ few V/cm Heat measurement (NTD sensor) @ 20
mK Discrimination between electron and
nuclear recoils Q ~ ionization/heat
« NTD » type : plain Al electrodes
Navick - LTD13 - Stanford - July 09
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Edelweiss I results and limits (2005)
Bad charge collection
Pb210 calibration
Charge collection deficit of electron like events : « surface » events Demonstrated 210Pb origin by calibration with 210Pb source
Navick - LTD13 - Stanford - July 09
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The Edelweiss-II experiment
Operated at the Underground Laboratory of Modane, 4800 mwe (4μ/day/m2)
Cryogenic installation (~ 20 mK) : Reversed geometry cryostat Use of pulse tubes
Can house up to 40 kg of detectors Shielding :
Clean room + deradonized air Active muon veto (>98% coverage) 50 cm PE shield, 20 cm Lead shield
⇒ γ background reduced by ~2 wrt EDW1 Facilities :
Remotely controlled sources for calibrations + regenerations
Detector storage & repair within clean room
12 cool-downs already operated
Navick - LTD13 - Stanford - July 09
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The muon veto in action
Ioni
zatio
n/re
coil
ratio
• Geant4 - expected : ~0.03 evts / kg.d• Mostly nuclear recoils below 50 keV
• Measured bolometer - muon veto coincidence rate : ~ 0.04 evts/kg.d
• The ionization yield distribution of coincidences is consistent with muon-induced events
2007-2008 data (280 kg.d - no cut)
spectra
• In addition: neutron detector installed to study induced n with higher stats
• Interactions in detectors due to muon-induced neutrons inside the shields
Navick - LTD13 - Stanford - July 09
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Physics run with « NTD » detectors
210Pb
210Po
206Pb
β
EDELWEISS-II93.5 kgd
Beta radioactivity at the surface of detectors• Incomplete charge collection• « Leakage » of such events down to the nuclear recoil region• Beta bkg reduced wrt EDW-I but stillinsufficient to reach 10-8 pb
EDW-II 2008 data :• 11 NTD detectors with < 30keV thresholds• 94 kg/d in 4 months• Threshold chosen a priori• =>3 events in nuclear recoil band
Navick - LTD13 - Stanford - July 09
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Surface event rejection : interleaved electrodes
‘b’ electrodes (+4V)
collecting‘a’ electrodes (-1.5V)
field shapping « VETO »
‘d’ (-4V) ‘c’ (+1.5V)
• Keep the EDW-I phonon sensor• Modify the E field near the surfaces with interleaved electrodes • Use ‘a’ and ‘c’ signals as vetos against surface events
First detector built 20071x200g + 3x400g tested in 200810x400g running since spring 2009
« ID » (interdigit) detector
Volume Guard
Surface
Navick - LTD13 - Stanford - July 09
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An outstanding surface event discrimination
Beta calibration(210Pb)200g detector
« single-side » surface events E1=0
« 3-electrode » surface events
46 keV gamma ray line
fiducial volume events
• Surface and volume events are completely separated !• From β calibration : overall rejection ~ 1/105
Preliminary
Navick - LTD13 - Stanford - July 09
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• A combination of cuts is madeon the signals of electrodes• Example here : cut on the difference of signals between 2 collecting electrodes
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IDs : overall background rejection performances
0 events
-equivalentto ~103 kgd
-equivalentto 3x104 kgd
arXiv:0905.0753
Navick - LTD13 - Stanford - July 09
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ID fiducial volume : background data
400g detector, background run
Fiducial volume cut
Preliminary
σion = 300 eV
Navick - LTD13 - Stanford - July 09
• Cosmogenic 68Ge, 65Zn lines @ 10 keV
• Background electron recoilsare homogeneously distributed in the volume of the crystal
• Fiducial volume = 160g, primarily limited by the guard regions
• Approx. ~ 20 kg.d of background data with two 400g detectors (2008 data)
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Physics run with IDs
2008 : • 86 live days / 4 months / 2x400g detectors• 18.3 kg.d with < 15 keV threshold, ~50% eff at 10keV
2009 : physics run ongoing• 10 detectors running (2kg fiducial)• x 20 improvement by 2010 : 4x10-8 pb• Additional new detectors w increased fiducial volume (« FIDs » 400g, 800g) => 9 kg fiducial mass end 2010
Background free
Preliminary
Navick - LTD13 - Stanford - July 09
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The future : EURECA
EURECA : beyond 10-9 pb, major efforts
in background control and detector
development
Joint effort from teams from
EDELWEISS, CRESST, ROSEBUD,
CERN, +others…
100 kg-1T cryogenic experiment, multi-
target : scintillators and Germanium
Part of ASPERA European Roadmap
Preferred site: 60 000 m2 extension of
present LSM (4 /m2/d), to be dig in
2011-2012
Design study start by end year
Start installation by 2013
Actual lab
Projected lab
EURECA : 2 cryostats in water tanks
Navick - LTD13 - Stanford - July 09
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Summary
Edelweiss-II now aiming at ~ 10-8 pb
Neutron shield and muon veto designed for < 10-8
New generation of « ID » detectors are validated Robust fabrication and operation Thresholds <15 keV Electron recoil rejection and surface event rejection (~1/105) Good fiducial volume - with improvements ongoing
ID detectors are well-fitted for future 100kg / ton-scale bolometric dark matter searches
Navick - LTD13 - Stanford - July 09
CEA Saclay (IRFU and IRAMIS) Detectors, electronics, acquisition, background, analysis E. Armengaud, O. Besida, G. Gerbier, M. Gros, X-F. Navick, B. Paul, S. Hervé, M. Karolak, (M. Chapellier), P.Pari Post-doc: M Hannawald Thesis : A. Chantelauze (cotutelle FZK), J Domange BDI CNRS, CSNSM Orsay Detectors, cabling, cryogenics, analysisL. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin,, F. Lalu, S. MarnierosPost-doc/ATER : E. Olivieri Thesis : O. Crauste, J Domange CNRS IPN Lyon Electronics, background, analysis, detectorsC Augier, F. Charlieux, M. De Jésus, P. Di Stefano, J. Gascon, A. Juillard, V. Sanglard, L. Vagneron,
Thesis : M. Luca, S. Scorza CNRS I Néel Grenoble Cryogenics, electronicsA. Benoit, M. Caussignac, H. Rodenas FZ/ Universität Karlsruhe Muon Veto and neutron counter, backgroundJ. Blümer, K. Eitel, Thesis : H. Kluck, A. Chantelauze (cotutelle FZK)Post doc : V Koslov JINR Dubna Monitoring of neutron and radon backgroundsE. Yakushev, S. Semikh Thesis : A. Lubashevski, L. Perevozchikov Oxford University High impedance sensors, wiring H. Kraus, S Henry, V Thesis : S Kierkby,
The Edelweiss IIcollaboration
Navick - LTD13 - Stanford - July 09
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