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Status of EDELWEISS-II

Status of EDELWEISS-II. Outline. EDELWEISS experiment EDELWEISS-I limits EDELWEISS-II setup EDELWEISS-II preliminary results. *Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP). The EDELWEISS collaboration. CEA Saclay CSNSM Orsay

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Status of EDELWEISS-II

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  1. Status of EDELWEISS-II

  2. Outline • EDELWEISS experiment • EDELWEISS-I limits • EDELWEISS-II setup • EDELWEISS-II preliminary results SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  3. *Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP) The EDELWEISS collaboration • CEA Saclay • CSNSM Orsay • IPN Lyon • Institut Néel Grenoble • FZ/ Universität Karlsruhe • JINR Dubna SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  4. EDELWEISS @ LSM (Laboratoire Souterrain de Modane) SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  5. Ionization threshold Neutrons 73Ge(n,n',) Gammas Heat and Ionization Ge detectors Heat Reference electrode Center electrode Guard ring Amorphous (Ge or Si) ~ 60 nm Thermometer (Ge NTD) Fiducial volume(≈ 57%) Ge crystal Guard Electrodes Center electrode Ionization guard 7 cm • Simultaneous measurement of • Heat @ 17 mK with Ge/NTD sensor • Ionization @ few V/cm with Al electrodes • Different charge/heat ratio for nuclear recoils (WIMP, neutrons) and electron recoils (, ) • EI/ER = 0.3 for nuclear recoils • EI/ER = 1 for electronic recoils • Event-by-event discrimination of electron recoils (main background) m=320g Ionization center SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  6. EDELWEISS-I (V.S. et al., PRD 71, 122002 (2005)) • 62 kg.d with 3 detectors • Best sensitivity up to 2003, but • Background • Neutrons : 1 n-n coincidence observed (2 singles expected by MC) • Surface electron recoils • Miscollected charge events at low energy • Leak of events down to the nuclear recoil band not visible in coincidence events • Rate compatible with 210Pb contamination ( rate ~ 5 / kg.d) SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  7. EDELWEISS-II setup • Cryogenic installation (~ 20 mK) • Reversed geometry cryostat • Dilution refrigerator + pulse tube • Room for up to 120 detectors • Shielding • Clean room + deradonized air (15 mB/m3) • 20 cm Pb • 50 cm PE • Active  veto (> 98% coverage) • Facilities • Remotely controlled sources for calibrations and regenerations • Remote operations (cryogeny, acquisition, …) • Detector storage and repair within the clean room • 9 cool-downs since January 2006 SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  8. EDELWEISS-II setup • Cryogenic installation (~ 20 mK) • Reversed geometry cryostat • Dilution refrigerator + pulse tube • Room for up to 120 detectors • Shielding • Clean room + deradonized air (15 mB/m3) • 20 cm Pb • 50 cm PE • Active  veto (> 98% coverage) • Facilities • Remotely controlled sources for calibrations and regenerations • Remote operations (cryogeny, acquisition, …) • Detector storage and repair within the clean room • 9 cool-downs since January 2006 SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  9. EDELWEISS-II detectors • “standard” Ge/NTD bolometers (320 g) as for EDELWEISS-I • Ge/NbSi bolometers (400 g) • “interdigit” Ge/NTD bolometers (200-400 g) SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  10. Results from “standard” NTD detectors • Commissioning background run (spring 2007) ~ 19 kg.d • 8 lowest threshold detectors selected • Only « pure center » events selected for better Ei resolution • Reduction of factor 3 of  and  background Ionization/Recoil Ratio Ionization/Recoil Ratio Recoil energy threshold (20-35 keV) SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  11. Results from “standard” NTD detectors • Commissioning background run (spring 2007) ~ 19 kg.d • 8 lowest threshold detectors selected • Only « pure center » events selected for better Ei resolution • Reduction of factor 3 of  and  background Ionization/Recoil Ratio Recoil energy threshold (20-35 keV) SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  12. Results from “standard” NTD detectors • Significant reduction of the  background • Calibration with  source (210Pb) to study the detector’s response to surface events • ~ 100 kg.d of fiducial exposure accumulated after quality cuts (analysis still underway) SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  13. Results from Ge/NbSi detectors • Developed @ CSNSM since 2003 • Goal : active identification of surface events using athermal phonon measurement with NbSi thin film thermometers • Each signal = thermal + athermal component • For surface events, athermal higher in corresponding thermometer • Thermal signals proportional to the deposited energy • Discrimination parameter = asymetry of athermal part of signals from the two surfaces • Surface rejection ok, some problems in 2007 with film contacts / leak currents • Resolutions hasn’t reached Ge/NTD performances SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  14. Results from Ge/NbSi detectors • Developed @ CSNSM since 2003 • Goal : active identification of surface events using athermal phonon measurement with NbSi thin film thermometers • Each signal = thermal + athermal component • For surface events, athermal higher in corresponding thermometer • Thermal signals proportional to the deposited energy • Discrimination parameter = asymetry of athermal part of signals from the two surfaces • Surface rejection ok, some problems in 2007 with film contacts / leak currents • Resolutions hasn’t reached Ge/NTD performances Data taken with 1 NbSi detector May & June 2007 ~ 1,5 kg.d fiducial SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  15. Results from Ge/Interdigit detector • Keep the standard phonon detector • Modify the E field near surfaces with interleaved electrodes (6 ionization channels) • Use B and D signals as vetos against surface events • From preliminary sea-level measurements • Surface event rejection > 95 % • Fiducial volume ~ 50 % A electrodes : + 2V B electrodes + 1V Z (cm) guard electrode G : + 1V A & B Near surface event A , B & C Event in low-field area Electrons trajectories A & C Bulk event holes trajectories guard electrode H : - 1V Radial coordinate (cm) C electrodes : - 2V D electrodes : - 1V SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  16. Results from Ge/Interdigit detector • Few kg.d of background runs @ LSM with a 200g detector • Performance as expected (resolutions, threshold, …) • Currently • 3 new 400g detectors • Precise measurement of  rejection • A promising detector with a simple design  calibration EDELWEISS-II ID-201 EDELWEISS-II ID-201 Neutron calibration SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  17. Results from Ge/Interdigit detector • Few kg.d of background runs @ LSM with a 200g detector • Performance as expected (resolutions, threshold, …) • Currently • 3 new 400g detectors • Precise measurement of  rejection • A promising detector with a simple design EDELWEISS-II ID-201 (4 kg.d) ER threshold < 20 keV No event below Q=0.5 SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  18. Current run (May 2008 - …) • Instrumented detectors: • 23 “standard” Ge/NTD bolometers • 5 “NbSi” bolometers • 4 “Interdigit” bolometers ~ 10 kg of Ge SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  19. Conclusion • “standard” Ge/NTD detectors • Improved background understanding : significant reduction of ,  and  backgrounds • 100 kg.d recorded and in analysis • Ge/NbSi detectors • Surface rejection ok • Resolution improvements needed • Ge/Interdigit detectors • December 2008 : 9 additional detectors • July 2009 : 120 kg.d fiducial exposure with threshold < 20 keV • Up to 35x320g Ge crystals available for reconfiguration as Ge/Interdigit SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

  20. EDELWEISS prospects • 1st Goal : • 4x10-8 pb in 2010 • Acquire physics data with 32 Ge/ID • 2nd Goal : • Few 10-9 pb in 2012 • ~ 70 detectors Ge/ID • EURECA (see H. Kraus’s talk next session) SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th

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