g. gerbier cea saclay, irfu, france blois, windows on the universe june 24th 2009
DESCRIPTION
Edelweiss-II : status and first results A new generation of background-free bolometers for WIMP search. G. Gerbier CEA Saclay, IRFU, France Blois, windows on the universe June 24th 2009. Reminder From EDWI to EDW II New ID detectors Some current results Outlook. astro-ph/08054705. KIMS. - PowerPoint PPT PresentationTRANSCRIPT
Edelweiss-II : status and first resultsA new generation of background-free bolometers for WIMP search
G. Gerbier
CEA Saclay, IRFU, France
Blois, windows on the universe
June 24th 2009
ReminderFrom EDWI to EDW IINew ID detectorsSome current resultsOutlook
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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/ionisation detectors :Subkev resolution on both channelslow thresholdsexcellent separation of populationsbackground and signal identification
• Also sensitive to electronic recoils, to inelastic DM…
Xe
Ge
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Phonon-ionization « NTD » sensors type
Edelweiss-I detectors Ionization measurement @ few V/cm Heat measurement (NTD sensor) @
20 mK Discriminating variable between
electronic and nuclear recoils : « Q » ~ ionization/heat
« NTD » type : plain Al electrodes
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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
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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 Hannewald 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
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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 Shieldings :
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
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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
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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
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Surface event rejection : phonon measurements
The CDMS way
• Athermal phonon measurement (transition-edge sensors on one side of the cristal)• Measurement of phonon risetime & delay surface e- rejected⇒
EDW « NbSi » R&D
• 2 NbSi films measuring athermal phonons + ionization signals• Surface event rejection ok• Pbs of threshold / reproducibility• Set aside
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Transient
Thermal
Heat signal of thermometer NbSiA :Surface event Bulk event
Thermometer Thermometer NbSiNbSi BB
Thermometer Thermometer NbSi NbSi AA Thermometer Thermometer NbSi NbSi AA
Thermometer Thermometer NbSiNbSi BB
Time (ms)
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Transient
Thermal
Heat signal of thermometer NbSiA :Surface event Bulk event
Thermometer Thermometer NbSiNbSi BB
Thermometer Thermometer NbSi NbSi AA Thermometer Thermometer NbSi NbSi AA
Thermometer Thermometer NbSiNbSi BB
200
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50
0
806040200
x10-3
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150
100
50
0
806040200
x10-3
Transient
Thermal
Heat signal of thermometer NbSiA :Surface event Bulk event
Thermometer Thermometer NbSiNbSi BB
Thermometer Thermometer NbSi NbSi AA Thermometer Thermometer NbSi NbSi AA
Thermometer Thermometer NbSiNbSi BB
Time (ms)
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Surface event rejection : interleaved electrodes
‘b’ electrodes (+2V)
collecting ‘a’ electrodes (-1V)field shapping « VETO »
‘d’ (-2V) ‘c’ (+1V)• Keep the EDW-I phonon sensor• Modify the E field near the surfaces with interleaved electrodes • Use ‘b’ and ‘d’ signals as vetos against surface events
First detector built 20071x200g + 3x400g tested in 200810x400g running since spring 2009
the « ID » (interdigit) detector
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Volume Guard
Surface
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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
• A combination of cuts is madeon the signals of electrodes• Example here : cut on the difference of signals between 2 collecting electrodes
•Surface and volume events are completely separated !• From β calibration : overall rejection ~ 1/105
Preliminary
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IDs : overall background rejection performances
0 events
-equivalentto ~103 kgd
-equivalentto 3x104 kgd
arXiv:0905.0753
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ID fiducial volume : background data
400g detector, background run
Fiducial volume cut
• Cosmogenic 68Ge, 65Zn lines @ 10 keV •Background electron recoilsare homogeneously distributed in the volume of the cristal• 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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Preliminaryσion = 300 eV
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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
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Preliminary
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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
Prefered 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
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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 improvments ongoing
ID detectors are well-fitted for future 100kg / ton-scale bolometric dark matter searches
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