From Edelweiss I to Edelweiss II Vronique SANGLARD

From Edelweiss I to Edelweiss II Véronique SANGLARD CNRS/IN 2 P 3/IPNL sanglard@ipnl. in 2 p 3. fr http: //edelweiss. in 2 p 3. fr 1

Outline The Edelweiss-I experiment 2003 results Ionization trigger data taking Phonon trigger data taking The second phase : Edelweiss-II Perspectives and conclusion V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 2

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) 6 4 µ/m²/d (10 less than at the surface) *Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP) V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 3

Heat and ionization detectors Ionization threshold Simultaneous measurement of charge and heat signals for each interaction Different charge/heat ratio for 73 Ge(n, n', γ) Neutrons Gammas nuclear and electron recoils (γs, βs ionize more than WIMPs Event by event discrimination and neutrons) Discrimination > 99. 9 % for E >15 ke. V rec V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 4

Charge collection Miscollected charge events can simulate nuclear recoils Use of gamma calibration (57 Co, 137 Cs) to check the detector charge collection quality Few miscollected charge events with amorphous layer Since 2002 use detectors with amorphous layer V. SANGLARD WITHOUT Identification of Dark Matter 2004 Edinburgh 07/09/04 5

The 1 kg stage Shield : 30 cm paraffin 15 cm lead 10 cm copper Al sputtered electrodes NTD heat sensor Ge or Si amorphous layer Guard ring fiducial vol. : 57 %* *(O. Martineau et al. Nim A in press) V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 6

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 : V. SANGLARD Events observed in nuclear recoil band (40 for Erec > 15 ke. V) Identification of Dark Matter 2004 Edinburgh 07/09/04 7

2003 data (ionization trigger) 20 kg. d Energy threshold : 20, 30 ke. V 3 events observed in the nuclear recoil band (above these thresholds) V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 8

2003 data (phonon trigger) Lower energy threshold : 15 ke. V 18 events observed in nuclear recoil band, most (12) below 30 ke. V in 22 kg. d 1 coincidence n-n observed between detectors (10% prob. ) Stable behavior of 3 detectors over total exposition V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 9

Edelweiss new limit Unknown backgrounds "Yellin method"* used to derive exclusion limit PRELIMINARY *(PRD 66, 032005 (2002)) No background subtraction New (prel. ) limit consistent with the previous publication* *(Phys. Lett. B 545 43 (2002)) V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 10

Experimental spectrum Low energy spectrum inconsistent with Wimp mass > ~ 20 Ge. V Possible backgrounds Neutrons (n-n coinc. ) Miscollected charge events (surface events) V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 11

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 Nb. Si thin film sensor Neutron background : V. SANGLARD Improved shielding against neutron Anti-coincidences more efficient with increased number of detectors Identification of Dark Matter 2004 Edinburgh 07/09/04 12

Identification of surface events 2 Nb. Si 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 Nb. Si 1 First tests of 200 g modules in Edelweiss-I promising : 10 x less background while retaining 50 % efficiency V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 13

Perspectives : Edelweiss-II Aim : x 100 improvement in sensitivity 1 st phase : V. SANGLARD 21*320 g Ge bolometers with NTD heat sensor 7*400 g Ge bolometers with Nb. Si thin film sensor Installation started in April 2004 Data taking in 2005 Identification of Dark Matter 2004 Edinburgh 07/09/04 14

Edelweiss II : new cryostat Larger experimental volume Low radioactivity cryostat Innovative reversed geometry 10 m. K base temperature First phase : 28 detectors, up to 120 V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 15

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 V. SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 16

Conclusion 2003 preliminary data confirm the 2002 exclusion limit Edelweiss-I is sensitive to -optimistic- SUSY models (10 -6 pb) Edelweiss-II, goals : V. SANGLARD 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 Identification of Dark Matter 2004 Edinburgh 07/09/04 17