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Véronique SANGLARD Université de Lyon, UCBL1 CNRS/IN2P3/IPNLyon sanglard@ipnl.in2p3.fr http://edelweiss.in2p3.fr Status of EDELWEISS-II
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th1 Outline EDELWEISS experiment EDELWEISS-I limits EDELWEISS-II setup EDELWEISS-II preliminary results
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th2 The EDELWEISS collaboration CEA Saclay CSNSM Orsay IPN Lyon Institut Néel Grenoble FZ/ Universität Karlsruhe JINR Dubna *Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th3 EDELWEISS @ LSM (Laboratoire Souterrain de Modane)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th4 Heat and Ionization Ge detectors 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 ( , ) E I /E R = 0.3 for nuclear recoils E I /E R = 1 for electronic recoils Event-by-event discrimination of electron recoils (main background) Neutrons 73 Ge(n,n', ) Gammas Ionization guard Ionization center Fiducial volume(≈ 57%) Heat Thermometer (Ge NTD) Reference electrode Center electrode Guard Electrodes Ge crystal Center electrode Guard ring 7 cm m=320g Ionization threshold Amorphous (Ge or Si) ~ 60 nm
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th5 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 210 Pb contamination ( rate ~ 5 / kg.d)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th6 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/m 3 ) 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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th7 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/m 3 ) 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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th8 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)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th9 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 Recoil energy threshold (20-35 keV) Ionization/Recoil Ratio
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th10 Results from “standard” NTD detectors Ionization/Recoil Ratio Recoil energy threshold (20-35 keV) 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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th11 Results from “standard” NTD detectors Significant reduction of the background Calibration with source ( 210 Pb) to study the detector’s response to surface events ~ 100 kg.d of fiducial exposure accumulated after quality cuts (analysis still underway)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th12 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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th13 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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th14 Results from Ge/Interdigit detector Radial coordinate (cm) Z (cm) guard electrode G : + 1V guard electrode H : - 1V A electrodes : + 2V B electrodes + 1V C electrodes : - 2V D electrodes : - 1V Electrons trajectories holes trajectories A & C Bulk event A, B & C Event in low-field area A & B Near surface event 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 %
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th15 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 Neutron calibration EDELWEISS-II ID-201 EDELWEISS-II ID-201
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th16 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 E R threshold < 20 keV No event below Q=0.5 EDELWEISS-II ID-201 (4 kg.d)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th17 Current run (May 2008 - …) Instrumented detectors: 23 “standard” Ge/NTD bolometers 5 “NbSi” bolometers 4 “Interdigit” bolometers ~ 10 kg of Ge
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th18 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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th19 EDELWEISS prospects 1 st Goal : 4x10 -8 pb in 2010 Acquire physics data with 32 Ge/ID 2 nd Goal : Few 10 -9 pb in 2012 ~ 70 detectors Ge/ID EURECA (see H. Kraus’s talk next session)
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