The EDELWEISS-II experiment

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

2. 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

3. EDELWEISS @ 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 σW-n≤ 10-8 pb <0.003 evts/kg/day (Er>10keV)

5. <300GeV> Veto Polyethylene n Cu(Cryostat) rock  Ge ´ Veto n Pb Gd-loaded scintillator p,π,α Pb 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: • Ionization @ few V/cm with Al electrodes • Heat@ 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, 122002 (2005) Problem: Surface electron recoils Interpretation: • Bad charge collection (trapping and recombination) • Indications of 210Pb contamination (exposition to Radon): • α rate ~ e rate ~ 4 /kg.day

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

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

11. Physics run: GeNTD Question: How to reach < 10-8 pb ? • 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 210Pb NEED • >1000 kgd at 15 keV threshold • >105 rejection for gammas • to reject expected >4000  from 210Pb Preliminary EDELWEISS 93.5 kgd IDea: Develop detectors with surface event rejection using interleaved electrode design (ID)

12. G B A B A B A A A B → → → → E E E E Fiducial volume Guard Electron trajectories hole trajectories C D C D C D C C D H ID detector • NTD heat sensor • E-field modified near surface with interleaved electrodes • B+D signals -> vetos % surface • 1x200g + 3x400g tested in2008 • 10x400g running ‘A’ electrodes: +2V ‘B’ electrodes: +1V Z (cm) guard ‘G’: + 1V ‘A&B’ near- surface event ‘A&C’ bulk event ‘A,B&C’ event in low-field area guard ‘H’: - 1V ‘C’ electrodes:-2V ‘D’ electrodes: -1V Radius (cm)

13. ID detector rejection • Beta rejection of 200g • Gamma rejection of 400g • ~1 month calibrations 6x104 210Po 6x104 210Bi 6x104 -equivalent to ~103 kgd -equivalent to 3x104 kgd 0 events

14. Physics run: ID detectors Conclusion: This is the good technology for 10-8 pb and beyond • 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

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 < 10-8 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

17. This is the end…

18. g46.5 keV (4%) 210Pb Cu few mm e-61 keV max 206Pb e-10keV - 100keV - 1MeV 22 yr 210Bi g 46 keV a 5 mm e-1.16MeV max Al 70nm ~50 nm 210Po NO ionisation amGe 70nm 206Pb a 350 nm 20 mm 100 keV 5.3 MeV Ge 2cm 700 mm 3 mm Decay Chain

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

20. EURECA - II

21. EURECA-I

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

24. Implantation of new lab First drawings nov 2006 (Lombardi eng company) G Gerbier EURECA ULISSE meeting- Lyon july 2008 24

25. Compatibility DAMA other experiments SI

26. Compatibility DAMA other experiments SD

27. Present limits

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

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