1. 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

2. 2 Direct search for WIMPs with cryogenic detectors astro-ph/08054705 KIMS EDELWEISS-I CRESST-II CDMS-II XENON 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 channels low thresholds excellent discrimination between populations background and signal identification Xe Ge Navick - LTD13 - Stanford - July 09

3. 3 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

4. 4 Edelweiss I results and limits (2005) Bad charge collection Pb210 calibration Charge collection deficit of electron like events : « surface » events Demonstrated 210 Pb origin by calibration with 210 Pb source Navick - LTD13 - Stanford - July 09

5. 5 The Edelweiss-II experiment Operated at the Underground Laboratory of Modane, 4800 mwe (4μ/day/m 2 ) 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

6. 6 The muon veto in action Ionization/recoil 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

7. 7 Physics run with « NTD » detectors 210 Pb 210 Po 206 Pb β EDELWEISS-II 93.5 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 still insufficient 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

8. 8 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 2007 1x200g + 3x400g tested in 2008 10x400g running since spring 2009 « ID » (interdigit) detector Volume Guard Surface Navick - LTD13 - Stanford - July 09

9. 9 An outstanding surface event discrimination Beta calibration ( 210 Pb) 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 ~ 1/10 5 Preliminary Navick - LTD13 - Stanford - July 09 2 A combination of cuts is made on the signals of electrodes Example here : cut on the difference of signals between 2 collecting electrodes

10. 10 IDs : overall background rejection performances 0 events -equivalent to ~10 3 kgd -equivalent to 3x10 4 kgd arXiv:0905.0753 Navick - LTD13 - Stanford - July 09

11. 11 ID fiducial volume : background data 400g detector, background run Fiducial volume cut Preliminary σ ion = 300 eV Navick - LTD13 - Stanford - July 09 Cosmogenic 68 Ge, 65 Zn lines @ 10 keV Background electron recoils are 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) 2

12. 12 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

13. 13 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 m 2 extension of present LSM (4 /m 2 /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

14. 14 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 (~1/10 5 ) 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

15. 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 HannawaldThesis : A. Chantelauze (cotutelle FZK), J Domange BDI CNRS, CSNSM OrsayDetectors, cabling, cryogenics, analysis L. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin,, F. Lalu, S. Marnieros Post-doc/ATER : E. OlivieriThesis : O. Crauste, J Domange CNRS IPN LyonElectronics, background, analysis, detectors C 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 GrenobleCryogenics, electronics A. Benoit, M. Caussignac, H. Rodenas FZ/ Universität KarlsruheMuon Veto and neutron counter, background J. Blümer, K. Eitel, Thesis : H. Kluck, A. Chantelauze (cotutelle FZK) Post doc : V Koslov JINR DubnaMonitoring of neutron and radon backgrounds E. Yakushev, S. SemikhThesis : A. Lubashevski, L. Perevozchikov Oxford UniversityHigh impedance sensors, wiring H. Kraus, S Henry, V Thesis : S Kierkby, The Edelweiss II collaboration Navick - LTD13 - Stanford - July 09