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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 The EDELWEISS collaboration
 CEA Saclay (DAPNIA & DRECAM) Detectors, background, analysis, electronics, acquisition E. Armengaud, O. Bessida, M. Chapellier, G. Chardin, G. Gerbier, H. Deschamps, M. Fesquet, M. Gros, S. Hassani, S. Hervé, M. Karolak, X-F. Navick, P.Pari, B. Paul Post-doc: R. Lemrani, F. Schwamm Thesis : E. Grémion, A. Chantelauze (cotutelle FZK)  CSNSM Orsay Detectors, cabling, cryogenics, analysis L. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin, A. Juillard, F. Lalu, S. Marnieros Post-doc: Emilano Olivieri Thesis : O. Crauste, X. Defay, Y. Dolgorouki, C. Nones  IPN Lyon Electronics, background, analysis, detectors F. Charlieux, M. De Jésus, P. Di Stefano, J. Gascon, M. Stern, V. Sanglard, L. Vagneron Thesis : S. Scorza, M.A.Verdier  IAP Paris Low radioactivity, analysis C. Goldbach, G. Nollez  CRTBT Grenoble Cryogenics, electronics A. Benoit, M. Caussignac, H. Rodenas  FZK/ Uni Karlsruhe (TH) Vetos, background N. Bechtold, J. Blümer, K. Eitel, V. Kozlov Thesis : A. Chantelauze (cotutelle CEA), H. Kluck  JINR Dubna Background E. Yakushev, A. Smolnikov Thesis : A. Lubashevski, L. Perevozchikov   50 persons (30 FET), 11 PhD theses, 3 post-docs

5 EDELWEISS @ Laboratoire Souterrain de Modane

6 Ge Heat-Ionization Detectors
Simultaneous measurements: few V/cm with Al electrodes 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

7 Edw-I limiting background
PRD71, (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/ E=5.3MeV Q=0.3 210Pb 210Po a b 206Pb

8 EDW – II set-up  radiopurity
dedicated HPGe detectors for systematic checks of all materials  clean room (class 100 around the cryostat, class 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) = evts/kg/day (Er>10keV)

9 Ge-NTD detectors 23*320g Ge/NTD : first low bg runs in 2006: old bg
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) 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 : evts/kg/day ( /m2/day) EDW-II  rate ~ 3 evts/kg/day new bg

10 Ge/NbSi detectors 7*400g 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 LSM data taken with 1 NbSi detector May&June 2007: 1.5kg.d (fiducial) 200 150 100 50 80 60 40 20 x10 -3 Transient T hermal Heat signal of thermometer NbSiA : Surface event Bulk event Thermometer NbSi B A Time (ms) Rejection works, resolutions needs tuning

11 ID detector lab data all events ‘a&b’ near- surface event ‘a&c’
‘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

12 status ID bolometer preliminary! 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!

13 EDELWEISS-II next steps
Goal 2x10-8 pb (1200 kg.d no event) (~1 evt/kg/y) acquire physics data with 23 NTD build 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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