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G. Gerbier CEA Saclay, IRFU, France Blois, windows on the universe June 24th 2009

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.

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G. Gerbier CEA Saclay, IRFU, France Blois, windows on the universe June 24th 2009

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  1. 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 Reminder From EDWI to EDW II New ID detectors Some current results Outlook

  2. astro-ph/08054705 KIMS EDELWEISS-I CRESST-II XENON CDMS-II Direct search for WIMPs with cryogenic detectors • 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 channels • low thresholds • excellent separation of populations • background and signal identification • Also sensitive to electronic recoils, • to inelastic DM… Xe Ge 2

  3. 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 3

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

  5. The Edelweiss IIcollaboration 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, analysis L. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin,, F. Lalu, S. Marnieros Post-doc/ATER : E. Olivieri Thesis : O. Crauste, J Domange CNRSIPN Lyon Electronics, 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 CNRSI Néel Grenoble Cryogenics, electronics A. Benoit, M. Caussignac, H. Rodenas FZ/ Universität Karlsruhe Muon Veto and neutron counter, background J. Blümer, K. Eitel, Thesis : H. Kluck, A. Chantelauze (cotutelle FZK) Post doc : V Koslov JINR Dubna Monitoring of neutron and radon backgrounds E. Yakushev, S. Semikh Thesis : A. Lubashevski, L. Perevozchikov Oxford University High impedance sensors, wiring H Kraus, S Henry, V Thesis : S Kierkby,

  6. 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 6

  7. The muon veto in action spectra • Interactions in detectors due to muon-induced neutrons inside the shields • 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 • In addition: neutron detector installed to study m induced n with higher stats Ionization/recoil ratio 2007-2008 data (280 kg.d - no cut) 7

  8. Physics run with « NTD » detectors 210Pb 210Po β a 206Pb • 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 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 8

  9. Surface event rejection : phonon measurements • EDW « NbSi » R&D • 2 NbSi films measuring athermal phonons + ionization signals • Surface event rejection ok • Pbs of threshold / reproducibility • Set aside • The CDMS way • Athermal phonon measurement (transition-edge sensors on one side of the cristal) • Measurement of phonon risetime & delay ⇒ surface e- rejected 9

  10. Surface event rejection : interleaved electrodes the « ID » (interdigit) detector ‘b’ electrodes (+2V) collecting ‘a’ electrodes (-1V) field shapping « VETO » Surface Guard Volume • 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 ‘d’ (-2V) ‘c’ (+1V) First detector built 2007 1x200g + 3x400g tested in 2008 10x400g running since spring 2009 10

  11. An outstanding surface event discrimination « single-side » surface events E1=0 Beta calibration (210Pb) 200g detector « 3-electrode » surface events 46 keV gamma ray line fiducial volume events • A combination of cuts is made • on 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 11

  12. IDs : overall background rejection performances arXiv:0905.0753 -equivalent to ~103 kgd -equivalent to 3x104 kgd 0 events 12

  13. ID fiducial volume : background data • Cosmogenic 68Ge, 65Zn lines @ 10 keV • Background electron recoils • are 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) 400g detector, background run Preliminary Fiducial volume cut σion = 300 eV 13

  14. Physics run with IDs Preliminary Background free • 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 14

  15. 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 15

  16. 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 16

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