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)

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

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

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

EDELWEISS @ Laboratoire Souterrain de Modane

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

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 210Pb 210Po a b 206Pb

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)

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) 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

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 2 @ 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

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

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!

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