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The EDELWEISS-II experiment

The EDELWEISS-II experiment. Silvia SCORZA Université Claude Bernard- Institut de Physique nucléaire de Lyon CEA-Saclay DAPNIA/DRECAM (FRANCE), CNRS/CRTBT Grenoble (FRANCE), CNRS/IN2P3/CSNSM Orsay (FRANCE), CNRS/IN2P3/IPN Lyon (FRANCE),

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The EDELWEISS-II experiment

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  1. The EDELWEISS-II experiment Silvia SCORZA Université Claude Bernard- Institut de Physique nucléaire de Lyon CEA-Saclay DAPNIA/DRECAM (FRANCE), CNRS/CRTBT Grenoble (FRANCE), CNRS/IN2P3/CSNSM Orsay (FRANCE), CNRS/IN2P3/IPN Lyon (FRANCE), CNRS/INSU/IAP Paris (FRANCE), CNRS-CEA/Laboratoire Souterrain de Modane (FRANCE), JINR Dubnia (RUSSIA), FZK/Universtat Karlsruhe (GERMANY)

  2. Outline • Limits of EDELWEISS-I • EDELWEISS-II setup • Current situation (3 detector types) • Outlook

  3. Direct Search Principle Detection of the energy deposited due to elastic scattering off target nuclei • Low energy threshold • Large detector mass • Low background • Radio – purity • Active/passive shielding • Deep underground sites • Event Rate : • < 1 ev /kg/week • Recoil Energy : • 1 – 100 keV

  4. EDELWEISS @ Laboratoire Souterrain de Modane

  5. Ge Heat-Ionization Detectors • Simultaneous measurements: • Ionization @ few V/cm with Al electrodes • Heat @ 17 mK with Ge/NTD sensor • Different Ionization/Heat energy ratio for nuclear and electronic recoils (dominate bkg) • Event by event background rejection => discrimination g/n > 99.9% for Er>15keV

  6. 210Pb 210Po b a Edw-I limiting background PRD71, 122002 (2005) Best Sensitivity up to 2003, but… Background in the physics data taking Leakage from the g to the recoil band • Neutrons: - 1 n-n coincidence observed - Neutron shield not thick enough • Surface electron recoils: -Bad charge collection (trapping and recombination) - Rate compatible with 210Pb contamination: rate a  “e-”  5/kg.day E=5.3MeV Q=0.3 206Pb

  7. EDW – II set-up • radiopurity dedicated HPGe detectors for systematic checks of all materials  clean room (class 100 around the cryostat, class 10000 for the full shielding)  deradonized air (from NEMO-3)  neutron shielding • 20 cm Pb shielding • 50 cm PE and better coverage • active m veto (>98% coverage) • up to 110 detectors • Ge/NTD + Ge/NbSi + new ID electrodes  expected sensitivity: EDW-I × 100 sc-n10-8 pb (phase 100) = 0.002 evts/kg/day (Er>10keV)

  8. Ge-NTD detectors • 23*320g Ge/NTD : • Developed by CEA Saclay and Canberra-Eurisys • Amorphous Ge and Si sublayer: better charge collection for surface evts • Optimized NTD size and homogeneous working T (16-18 mK) : goal keV resolution • New holder and connectors (Teflon and copper only) • All @ LSM first low bg runs in 2006: old bg • EDW-I g rate: ~ 700 evts/kg/day for E>100keV • After the most recent improvement EDW-II g rate: ~ 300 evts/kg/day • EDW-I  rate on central electrode : 2.5 - 5.5 evts/kg/day (400-1000 /m2/day) • EDW-II  rate ~ 3 evts/kg/day new bg

  9. Thermometer Thermometer Thermometer NbSi NbSi NbSi A A A Thermometer Thermometer Thermometer NbSi NbSi NbSi A A A Thermometer Thermometer Thermometer NbSi NbSi NbSi A A A Thermometer Thermometer Thermometer NbSi NbSi NbSi A A A Thermometer Thermometer Thermometer NbSi NbSi NbSi B B B Thermometer Thermometer Thermometer NbSi NbSi NbSi B B B Thermometer Thermometer NbSi NbSi B B Thermometer Thermometer NbSi NbSi B B Thermometer NbSi B Thermometer NbSi B Heat signal of thermometer Heat signal of thermometer NbSiA NbSiA : : Heat signal of thermometer NbSiA : 200 200 200 200 200 200 Surface event Surface event Surface event Bulk event Bulk event Bulk event 150 150 150 150 150 150 Transient Transient Transient 100 100 100 100 100 100 T T T hermal hermal hermal 50 50 50 50 50 50 0 0 0 0 0 0 0 0 0 20 20 20 40 40 40 60 60 60 80 80 80 0 0 0 20 20 20 40 40 40 60 60 60 80 80 80 -3 -3 -3 -3 -3 -3 x10 x10 x10 x10 x10 x10 Time (ms) Time (ms) Ge/NbSi detectors identification of surface events with Ge/NbSi detector • 7*400g Ge/NbSi detectors : • developed by CSNSM Orsay • NbSi thin film thermometers for active surface evt rejection • 2 @ LSM data taken with 1 NbSi detector May&June 2007: 1.5kg.d (fiducial) Rejection works, resolutions needs tuning

  10. ID detector ‘a’ electrodes: +2V after cut “b” < 5keV (30% of evts. survive) all events ‘b’ electrodes: +1V Z (cm) guard ‘g’: + 1V recoil energy [keV] recoil energy [keV] ‘a&b’ near- surface event lab data Electron trajectories 200g detector, concentric electrodes 2mm gaps, 200µm width trigger thresh. 24keV 241Am source with 60keV g´s ‘a&c’ bulk event ‘a,b&c’ event in low-field area hole trajectories guard ‘h’: - 1V ‘d’ electrodes: -1V Radius (cm) ‘c’ electrodes:-2V

  11. status ID bolometer • summary: • first detector (200g) with • interleaved electrodes in LSM • performance as expected New 400g ID´s to be installed end of March ~1.7 kg.d preliminary!

  12. EDELWEISS-II next steps • Goal 2x10-8 pb (1200 kg.d no event) (~1 evt/kg/y) • acquire physics data with 23 NTD • build 6 400 g NbSi • Goal 2x10-10 pb (~10 evt/t/y) • build 16 NbSi (same/tuned if needed) • build 24 NTD with reduced contamination and/or with ID electrodes

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