1. The GENIUS dark matter project Laura Baudis Stanford University

2. The GENIUS collaboration MPIK Heidelberg Kurchatov Institute Moscow Dubna Nijnii Novgorod...

3. Direct detection of WIMPs elastic scattering off nuclei (Goodman, Witten 1985): look for the energy deposited by the recoiling nucleus  0 ~ 0.3 - 0.5 GeV/cm 3 v ~ 220 km/s, MB-distrib good candidate from SUSY: LSP m = 10 - 1000 GeV  < 10 -41 cm 2 event rate < 1 event/kg d recoil energy < 100 keV dn/dE r ErEr Expected recoil spectrum

4. muon g-2 measurement If due to SUSY: upper bound on the neutralino mass: 500 GeV minimum cross section is large: 10 -9 pb CDMS I CDMS II Baltz-Gondolo 01 GENIUS

5. GErmanium in liquid NItrogen Setup L. Baudis et al., NIMA 99 Proposal: hep-ph/9910205 array of 40 natural HPGe detectors in Li N (100kg) goal: reach the extremely low background of 1 ev/100 kg y keV below 100 keV test a large part of MSSM parameter space for neutralinos

6. GENIUS: detection technique ionization in p-type HPGe detectors no recoil discrimination single/multiple events give some background reduction Main background reduction: by operating naked Ge crystals directly in liquid nitrogen

7. Naked Ge detectors feel well in liquid nitrogen contacts established using only 3 g of material (stainless steel to fix inner and outer contacts) here: test detector (425 g) held on kevlar wires

8. Performance in LiN no electrical interference no microphonics up to 6m cables between crystals and FETs resolution: 1 keV @ 300 keV threshold: 2.5 keV 133 Ba background

9. Possible location: Gran Sasso

10. Possible layout study in collab. with Messer-Griesheim, Germany

11. Design of the holder system 1,2 or more concentric layers of Ge crystals holder made of high molecular PE

12. Background expectations Monte Carlo simulations based on GEANT3.21 + GCALOR Geometry: 12 x 12 m tank, 2 m PE foam, 2 mm steel walls, holder system of HD1000, 40 Ge detectors, muon veto on top of the tank External background: photon and neutron flux from rock muon interactions + induced activities Internal background: intrins. contam. of LiN, steel vessel, holder system, Ge-crystals activation of Ge and LiN at sea level

13. External background simulation of measured  and n-flux in GS ComponentEvents/100 kg y keV (<100 keV) gammas0.4 neutrons0.04 muon showers0.2 muon -> n0.1 muon capture<< 0.01 goal1 12 m tank 2m borated PE foam muon veto: 96 % eff.

14. Internal background SourceRadionuclidePurityCount rate/ 100 kg yr keV Liquid nitrogen 238 U 232 Th 40 K 222 Rn 3.5 x 10 -16 g/g 4.4 x 10 -16 g/g 1.0 x 10 -15 g/g 3  Bq/m 3 0.07 0.04 0.01 0.03 Holder system 238 U/ 232 Th 1.0 x 10 -12 g/g0.0015 Steel vessel 238 U/ 232 Th 5.0 x 10 -9 g/g0.08 GOAL1

15. Cosmogenics in Germanium assumptions: 10 days @ sea level 68 Ge: saturration 3 yr below ground activity 3 H, 49 V, 54 Mn, 55 Fe, 57 Co, 60 Co, 65 Zn, 68 Ge 3H3H   Q = 18.6 keVT 1/2 = 12.35 yr 68 GeECE(K a ) = 10.37 keV Q EC ( 68 Ga) = 2921 keV T 1/2 = 270 d

16. 3 H, 68 Ge assumptions: 10 days @ sea level 68 Ge: saturration 3 yr below ground activity 3H3H   3.6  Bq/kg ~113 decays/yr 200 ev/100 kg yr keV (12-19 keV) 68 GeEC 28  Bq/kg 1.1 ev/100 kg yr keV solutions? 3 H: shielded production 1m heavy concrete ~ 5 mwe: factor 30 1 d transportation: factor 10 better: produce detectors in undeground lab! 68 Ge: decays after another 2 yr, subtract 10.37 keV line start early with detector production, store underground

17. Cosmogenics in LiN IsotopeT 1/2 Energy [keV] Activity [Bq/g] Rate/ 100kg yr keV 3H3H12.3 y 18.6 (  - ) 3.8 x 10 -8 negligible 7 Be53.3 d 477.6 (  ) 3.7 x 10 -9 0.8 10 Be1.6 x 10 6 y 555 (  - ) 8 x 10 -15 negligible 14 C5.7 x 10 4 y 156 (  - ) 1.4 x 10 -4 0.01 Goal1 10 d transportation @ sea level

18. Other background sources radionuclide production in Ge/LiN by  induced sec. n: 14 N(n,x) a B, 70,72,73,74,76 Ge(n,x) a B negativ muon capture in LiN -> rates and decays of produced isotopes:  - + (7,14) -> (6, 14) * +  (6,14) * -> (Z ‘,A ‘ ) + (1-4)n, ,p inelastic muon scattering:  + N ->  ‘ + X * contributions are not relevant

19. Expectations for GENIUS GENIUS CDMS Soudan CRESST HDMS CDMS 2000 DAMA 3  V. Mandic, R. Gaitskell with 100 kg Ge: detect WIMP signature via annual modulation

20. current status? GENIUS Test Facility is approved and being installed @ GS

21. Genius Test Facility borated PE 14 natural (40 kg) HPGe in a volume of 0.064 m 3 of ultra-pure LiN 0.5 mm steel vessel 0.9 x 0.9 x 0.9 m polystyrene 5 cm inner shield of HPGe 10 cm low level Cu 30 cm of Pb 15 cm borated PE L. Baudis et al., hep-ex/0012022 2 m x 2m

22. Genius-TF goals background: 2 events/ kg y keV: 0 - 50 keV: factor of 10 better than Heidelberg-Moscow test material purities down to this level design of crystal support system new DAQ and electronics reliability of calculation of cosmogenic production long-term stability of naked HPGe in LiN

23. Background estimations MC simulations: photon, neutron, muon flux in GS intrinsic radioactivity of: liquid nitrogen steel vessel polystyrene foam Ge, Cu shields crystal holder system Ge crystals + cosmogenic activation of Ge and Cu

24. Assumptions for material purities Ge crystalsupper limit HM LiN1000 x Borexino Rn in LiN 325  Bq/m 3 (Heusser 2000) SteelHd (Heusser 2000) Ge bricks100 x limit HM Polystyrenefirst measurements in HD CopperHM (cosmo + anthro) Holder systemSNO meas. for acryl

25. Cosmogenics in Ge 30 days production + transportation @ sea level 1 year de-activation below ground

26. Sumspectrum

27. Genius-TF: expectation based on: 2 events/kg y keV 1 yr exposure 2 keV/11 keV threshold

28. Genius-TF & WIMP signature E th = 2 keV (11 keV) B = 4 events/kg y keV M = 40 kg (nat) Ge 0.4 - 1.4 yr (1.3 - 5 yr) exposure required to see the DAMA signal with 50% - 90% probability and 99.5 % CL (S. Cebrian et al., Astrop. Phys. 14 (2001), hep-ph/9912394) but: new detectors -> E th = 0.5 keV! will significantly improve the sensitivity to the annual modulation signature good chance to see an annual modulation

29. Status of Genius-TF Infrastructure built at Gran Sasso 5 detectors are ready (crystals + signal/HV contacts) Cold hardware is being built in Heidelberg New electronics: MPIK, Heidelberg Setup to be installed in GS during the next months First results expected by end of 2002

30. Conclusions for GENIUS technology: simple, well understood production of 40 HPGe detectors: straightforward LiN purification method proved by BOREXINO 1 event/100 kg yr keV can be reached if: tank diameter: 12 m production of cosmogenics in Ge minimized surface contaminations under control cover large part of M W -  parameter space detect a WIMP signature

31. backup slides

32. Muon induced neutrons

33. Negative muon capture