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From Edelweiss I to Edelweiss II

Véronique SANGLARD CNRS/IN2P3/IPNL sanglard@ipnl.in2p3.fr http://edelweiss.in2p3.fr. From Edelweiss I to Edelweiss II. Outline. The Edelweiss-I experiment 2003 results Ionization trigger data taking Phonon trigger data taking The second phase : Edelweiss-II

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From Edelweiss I to Edelweiss II

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  1. Véronique SANGLARD CNRS/IN2P3/IPNL sanglard@ipnl.in2p3.fr http://edelweiss.in2p3.fr From Edelweiss I to Edelweiss II

  2. Outline The Edelweiss-I experiment 2003 results Ionization trigger data taking Phonon trigger data taking The second phase : Edelweiss-II Perspectives and conclusion

  3. The Edelweiss* collaboration CEA-Saclay DAPNIA/DRECAM CRTBT Grenoble CSNSM Orsay FZK/Univ. Karlsruhe IAP Paris IPN Lyon Laboratoire Souterrain de Modane 1700 m depth under the Fréjus tunnel (4800 we) 4 µ/m²/d (106 less than at the surface) *Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP)

  4. Heat and ionization detectors Ionization threshold Simultaneous measurement of charge and heat signals for each interaction Different charge/heat ratio for nuclear and electron recoils (γs, βs ionize more than WIMPs and neutrons) Neutrons 73Ge(n,n',γ) Gammas Discrimination > 99.9 % for Erec>15 keV Event by event discrimination

  5. Charge collection Miscollected charge events can simulate nuclear recoils Use of gamma calibration (57Co, 137Cs) to check the detector charge collection quality Few miscollected charge events with amorphous layer Since 2002 use detectors with amorphous layer WITH WITHOUT

  6. The 1 kg stage Shield : 30 cm paraffin 15 cm lead 10 cm copper Al sputtered electrodes Ge or Si amorphous layer Guard ring fiducial vol. : 57 %* *(O.Martineau et al. Nim A in press) NTD heat sensor

  7. 2003 Edelweiss data Additional ~45 kg.d recorded with 3 new detectors 2 phases with 2 different triggers On the ionization signal On the phonon signal 2000-2003 data represent ~ 62 kg.d Results : Events observed in nuclear recoil band (40 for Erec > 15 keV)

  8. 2003 data (ionization trigger) • 20 kg.d • Energy threshold : 20, 30 keV • 3 events observed in the nuclear recoil band (above these thresholds)

  9. 2003 data (phonon trigger) • Lower energy threshold : 15 keV • 18 events observed in nuclear recoil band, most (12) below 30 keV in 22 kg.d • 1 coincidence n-n observed between detectors (10% prob.) • Stable behavior of 3 detectors over total exposition

  10. Edelweiss new limit • Unknown backgrounds "Yellin method"* used to derive exclusion limit *(PRD 66,032005 (2002)) • No background subtraction • New (prel.) limit consistent with the previous publication* *(Phys. Lett. B 545 43 (2002)) PRELIMINARY

  11. Experimental spectrum • Low energy spectrum inconsistent with Wimp mass > ~ 20 GeV Possible backgrounds • Neutrons (n-n coinc.) • Miscollected charge events (surface events)

  12. Lessons from Edelweiss-I • With 3 new detectors and an extended exposure, the preliminary 2003 exclusion limit confirms the previous published one • Surface events : • Improved radiopurity in Edelweiss-II • Identification (or suppression) possible with NbSi thin film sensor • Neutron background : • Improved shielding against neutron • Anti-coincidences more efficient with increased number of detectors

  13. Identification of surface events • 2 NbSi athermal phonon sensors for surface event rejection • Two components : • Thermal (energy) • Athermal/transitory (near-surface tag) • For this surface event, the athermal component is higher in NbSi 1 • First tests of 200g modules in Edelweiss-I promising : • 10 x less background while retaining 50 % efficiency

  14. Perspectives : Edelweiss-II Aim : x 100 improvement in sensitivity 1st phase : 21*320g Ge bolometers with NTD heat sensor 7*400g Ge bolometers with NbSi thin film sensor Installation started in April 2004 Data taking in 2005

  15. Edelweiss II : new cryostat • Larger experimental volume • Low radioactivity cryostat • Innovative reversed geometry • 10 mK base temperature • First phase : 28 detectors, up to 120

  16. Edelweiss II : new setup • Clean room • Efficient shielding against neutron and gamma ray background • 20 cm lead • 50 cm PE • Muon veto • Sensitivity • Edelweiss I : 0.2 evt/kg/day • Edelweiss II : 0.002 evt/kg/day

  17. Conclusion 2003 preliminary data confirm the 2002 exclusion limit Edelweiss-I is sensitive to -optimistic- SUSY models (10-6 pb) Edelweiss-II, goals : To reach more favored SUSY models (10-8 pb) Competitive with CDMS-II, CRESST-II Testing the bulk of SUSY parameter space (>10-10 pb) will require one-ton detector array and an extreme background rejection

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