EDELWEISSLatest Results and Future Plans
Edelweiss collaboration:CEA Saclay (IRFU, IRAMIS), CSNSM Orsay (CNRS/IN2P3 + Univ. Paris Sud), Karlsruhe Institute of
Technology (IEKP, IKP, ITP), Institut Néel Grenoble (CNRS/INP), IPN Lyon (CNRS/IN2P3 + Univ. Lyon 1), Laboratoire Souterrain de Modane , JINR Dubna , University of Oxford , University of Sheffield
Hans Kraus, University of Oxford
on the behalf of the EDELWEISS collaboration
Karlsruhe – Oct.2009 Oxford – Sept. 2010
J. Gironnet - IPNL - Patras 2011
Expérience pour DEtecterLes Wimps En SIteSouterrain
• Search for WIMP dark matter (scattering:~10keV nuclear recoil with <0.01 events/kg/day)
• Need:
• Sensitive Detectors (cryogenic germanium phonon-ionization detectors)
• Low background (passive shielding and ultra-low background materials)
• Excellent background discrimination(active rejection by muon vetoing and surface event identification)
• Extended running periods / stability(good cryostat performance and calibrations)
• Laboratoire Souterrain de Modane
� Place: Laboratoire Souterrain de MODANEcosmic muon flux: 4 µ/m2/day
� Cryogenic installation (18 mK):� Reversed geometry cryostat, pulse tubes� Remotely controlled� Can host up to 40kg of detectors
� Shieldings:� Clean room + de-radonized air� Active muon veto (>98% coverage)� 50-cm PE shield� 20-cm lead shield
� Other items :� Remotely controlled sources for gamma
calibrations + regenerations� AmBe sources of neutron calibrations� Radon detection down to few mBq/m3
�3He neutron detector (thermal neutron monitoring inside shields) sensitivity ~10−9
n/cm2/s� Liquid scintillator neutron counter (study of
muon-induced neutrons)Global setup view
The EDELWEISS-II infrastructure
FRANCE ITALIE
AltitudesDistances
1228 m 1298 m1263 m0 m 6210 m 12 868 m
4800 mwe
3
EDELWEISS I – Detectors
Target:Ge crystalPhonon - signal:NTD-Ge (~ 20 mK)Ionisation - signal:Inner disc / outer guard ringfew V/cm
� Event by event background discrimination
� Limitation: surface events
Target:Ge crystalPhonon - signal:NTD-Ge (~ 20 mK)Ionisation - signal:Inner disc / outer guard ringfew V/cm
� Event by event background discrimination
� Limitation: surface events
EDELWEISS I – Detectors
Target:Ge crystalPhonon - signal:NTD-Ge (~ 20 mK)Ionisation - signal:Inner disc / outer guard ringfew V/cm
� Event by event background discrimination
� Limitation: surface events
EDELWEISS I – Detectors
EDELWEISS II InterDigit (ID) detectors
Bulk events: charge only on fiducial
electrodes (A & C)
A: +4 V
B: −1.5V
C: −4 V
D: +1.5VSurface event (β)
rejection: 105
Surface events:charge on veto electrodes
(B, D, guard rings)
A. Broniatowski et al Phys Lett B 681 (2009) 305 [arXiv:0905.0753]
ID detectors – surface event rejection
A. Broniatowski et al Phys Lett B 681 (2009) 305 [arXiv:0905.0753]
Surface event (β) rejection: 6×10–5
(90% CL)
210Pb Calibration
6×104 β events
WIMP search: final results
Five WIMP candidates:- 4 evts: 20.8 < E < 23.2 keV- 1 evt @ 172 keV
alpha tail
fiducial volume events, 427 kg.d
• Gamma background – 1.8×104 events (20-200keV) 133Ba calibrations → 3×10−5 leakage into NR band
→ <0.9 events
• Surface events – 5000 events, rejection factor 6×10−5
→ 0.3 events
• Muon induced events missed by veto → <0.4 events
• Neutrons from rock – GEANT4 simulations → <0.11 events
• Neutrons from contaminants in shield/cryostat → <0.21 events
• Neutrons from connectors / cabling in cryostat → <1.1 events
Edelweiss II Background estimate
Total background estimate: 3.0 events
EDELWEISS II ResultsPreliminary result: Physics Letters B 687 (2010) 294-298
Final result: Accepted for publication in Physics Letters B. [arXiv:1103.4070v2]
[CDMS December 2009 result: 3.8×10-8pb, 2 nuclear recoil events]
• Run April 2009 - May 201014 months of continuous operation@ 20mK (85% duty cycle)
• 10 x 400g ID Ge detectors, 384kg day
• 4.4×10-8pb excluded for 85GeV WIMP
• Five nuclear recoil events (above20keV analysis threshold)
• Background estimate: 3.0 events
Results – inelastic scattering
• WIMP-nucleus scattering → excited state
• Mass splitting δ~120keV, DAMA region excluded above 90GeV
Elastic WIMP scattering limits: similar sensitivitiesfrom CDMS and EDELWEISS
arXiv:1103.4070Limits very close, with same target nucleus: why not combine data?
� “Simple merger method”
� More sophisticated ones also used in paper
� Strong and efficient collaboration allowed completion of analysis within few months
CDMS+EDELWEISS: the data
CDMS+EDELWEISS: the limits
EDELWEISS III: new detectors FID800 (2010)
• All fiducial volume: more statistics than stackedID-400 statistics
• No event in NR
• Expected to be and isindeed better than IDs!
Preliminary
ID (350000 γ)
Fiducialmass~600g
Towards 5×10−9 pb: EDELWEISS III
Programme under way, funded.
Detector improvements:
• ~40 FID800 detectors to be installed early 2012: 24kg fiducial
• 2 NTD heat sensors (better heat ch), 4 ionization channels, instead of 6.
Infrastructure improvements:
• Within the Edelweiss-II setup –upgrades of cryogenics, cabling, DAQ, shielding.
• Extra internal PE shield.
• Dark matter experiment, to search for WIMP interactions to σ~10-10pb (~1 event/tonne/year)
• CRESST and EDELWEISS, and additional groups
• Cryogenic (<100mK) calorimeters
• Multiple target materials: Ge, CaWO4, ZnWO4….
• Mass: above 100 kg towards 1 tonne
European Underground Rare Event Calorimeter Array
Indication, Confirmation, Study
XENON 100
CDMSEDELWEISS
ZEPLIN III (FSR)
100 kg – 1000 kg projections
Timeline:
2010/2011: Design Study � TDR
2011/12: Digging at LSM. Machine starts Sept 2011 at 20m/d. Begin construction of EURECA components away from LSM. Aim for ~150kg stage (10−9 pb).
2014: LSM extension ready to receive EURECA.
2015: Begin data taking and in parallel improve and upgrade.
2018: One tonne target installed.
Spokesman: Hans Kraus (2005-2010), since January 2011: Gilles Gerbier
Existing laboratory
Summary
• Edelweiss-II: Direct WIMP search with cryogenic germanium detectors
• Interleaved electrodes allow surface event rejection
• Ten 400 g Ge-ID detectors – 384 kg day• 4.4×10-8 pb excluded for 85 GeV WIMP• Nuclear recoils: 5. • Expected background: 3. (gamma, beta leakage,
neutrons from cosmic muons, radioactivity)• …Edelweiss-III (5×10-9 pb)….EURECA (10-10 pb)