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 Dubna (RUSSIA), FZK/Universtat Karlsruhe (GERMANY)

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

3 LSM

4 EDW–II set-up Radiopurity dedicated HPGe detectors for systematic checks of all materials Strict control of bkg: material selection/cleaning procedure/Environment  Shielding 20 cm Pb shielding 50 cm PE and better coverage active μ veto (> 98% coverage) Up to 110 detectors -> 40kg Ge detector Ge/NTD Develop new ID detectors  Goal: EDW-I × 100 σ W-n ≤ pb 10keV)

5 µ-veto Candidates for coincident veto-bolometer events Accidental coincidences Expected from Geant4 simulation: ~0.03 events/kg.d Measured: 0.04 events/kg.d

6 Ge Heat-Ionization Detectors Simultaneous measurements: few V/cm with Al electrodes 20 mK with Ge/NTD sensor Different Ionization/Heat energy ratio for nuclear and electronic recoils (dominate bkg)

7 Event by event background rejection

8 Edw-I limiting background PRD71, (2005) Problem: Surface electron recoils Interpretation: Bad charge collection (trapping and recombination) Indications of 210 Pb contamination (exposition to Radon):  α rate ~ e rate ~ 4 /kg.day

9 206 Pb β 210 Pb 210 Po  210 Po 210 Pb 210 Pb source

10 GeNTD data: improved bkg Gamma background: reduction of x3 relative to EDELWEISS-I 210 Pb-chain background: reduction of x2 relative to EDELWEISS-I EDW-I ~4 /kgd EDW-II ~2 /kgd 5 kgd 95 kgd preliminary Full volume Further bkg reductions after fiducial + coincidence cuts Conclusion: Reduction of background from EDW-I to EDW-II

11 Physics run: GeNTD 11 detectors with <30 keV threshold Threshold chosen before start of run (EDW-I results  expected  bkg) 93.5 kg.day 3 events observed in nuclear recoil band 31, 31 and 42 keV Evidence for events with deficient charge collection from 210 Pb Preliminary EDELWEISS 93.5 kgd Question: How to reach < pb ? NEED  >1000 kgd at 15 keV threshold  >10 5 rejection for gammas  to reject expected >4000  from 210 Pb IDea : Develop detectors with surface event rejection using interleaved electrode design (ID)

12 A A AAA B BBB C CCCC D DDD G H GuardFiducial volume → E → E → E → E ‘A’ electrodes: +2V ID detector Radius (cm) Z (cm) guard ‘G’: + 1V guard ‘H’: - 1V ‘C’ electrodes:-2V ‘D’ electrodes: -1V Electron trajectories hole trajectories ‘A&C’ bulk event ‘A&B’ near- surface event ‘A,B&C’ event in low-field area  NTD heat sensor E-field modified near surface with interleaved electrodes B+D signals -> vetos % surface 1x200g + 3x400g tested in x400g running ‘B’ electrodes: +1V

13 ID detector rejection Gamma rejection of 400g ~1 month calibrations Beta rejection of 200g -equivalent to 3x10 4 kgd 6x Bi 6x Po 0 events -equivalent to ~10 3 kgd

14 Physics run: ID detectors 1 x 400g + 1 x 350g detectors, 86 live days <15 keV threshold achieved for exposure of 18.6 kg.days 50% efficiency at 10 keV No events in (or around) nuclear recoil band Conclusion: This is the good technology for pb and beyond

15 Limits 93.5 kgd GeNTD 11 detectors x 4 months 30 keV threshold 3 events observed in nuclear recoil band 18.3 kgd ID 2 detectors x 4 months 15 keV threshold No nuclear recoils No evts outside  band 2009: 10 ID detectors improvement in sensitivity: 4x10 -8 pb More detectors build in 2009 Preliminary

16 Conclusions/Outlook Significant reduction in , β and γ backgrounds relative to EDELWEISS-I Improved understanding of backgrounds and of response of detectors to backgrounds Improved limit relative to EDELWEISS-I Passive background reduction alone not sufficient to reach < pb ID detectors have the surface rejection needed to reach this goal Running in 2009 with 10 x 400g detectors Prototype of ID detectors with larger fiducial volumes currently in test EURECA = 1 ton scale experiment (CRESST, EDELWEISS, CERN, LSM extension

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18 Decay Chain 210 Po 206 Pb  5.3 MeV100 keV Al 70nm amGe 70nm Ge 2cm 206 Pb  e - 10keV - 100keV - 1MeV Cu few mm 5 mm ~50 nm 350 nm 20  m 700  m 210 Bi e MeV max 210 Pb e - 61 keV max  46.5 keV (4%)  46 keV 3 mm NO ionisation 22 yr

19 EDELWEISS-II 210 Pb source calibration Confirms interpretation of EDW-I bkg as 210 Pb surface . Response of detectors to this important background 210 Pb 206 Pb β 210 Po  E=5.3 MeV Q~0.3 Edw-I data EDELWEISS-II 210 Pb source 210 Pb 210 Po 206 Pb recoils coincident with 210 Po  210 Bi Edw-II Implantation depth of 210 Pb

20 EURECA - II

21 EURECA-I

22

23 France-Italy Fréjus tunnel : new safety gallery planned Existing road tunnel Existing lab s ?  2 projects  Limited extension  Very large cavity

24 G Gerbier EURECA ULISSE meeting- Lyon july Implantation of new lab First drawings nov 2006 (Lombardi eng company)

25 Compatibility DAMA other experiments SI

26 Compatibility DAMA other experiments SD

27 Present limits

28 Number of events in WIMP region: q< 0.5, 25 < E < 60 кэВ registered 23 events Experimental data Alpha rate 2.5 events

29 N alphas in calibration spectrum = 3040 events Number of events in WIMP region: q< 0.5, 25 < E < 60 кэВ registered = 460 events 460 events Expected number events from calibration with 210 Pb = 37 events Estimation of background from 210 Pb