EDELWEISS-II : Status and future Véronique SANGLARD CNRS/IN2P3/IPNLyon

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 2 Outline Context EDELWEISS-I Run with heat trigger Final results Background studies EDELWEISS-II Improvements Present and future runs Conclusion

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 3 The EDELWEISS Collaboration CEA-Saclay DAPNIA/DRECAM CNRS/CRTBT Grenoble CNRS/IN2P3/CSNSM Orsay DUBNA (Russia) FZK/Univ. Karlsruhe (Deutschland) CNRS/INSU/IAP Paris CNRS/IN2P3/IPN Lyon CNRS – CEA/Laboratoire Souterrain de Modane 1700 m depth under the Fréjus tunnel (4800 we) 4 µ/m²/d (10 6 less than at the surface) *Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 4 Heat and Ionization Ge detectors Simultaneous measurement of 17 mK with Ge/NTD sensor few V/cm with Al electrodes Different charge/heat ratio for nuclear and electron recoils (WIMP and neutron have lower light/charge than γs, βs ) Discrimination event-by- event of electron recoils (main background) E I /E R = 0.3 for nuclear recoils E I /E R = 1 for electronic recoils Neutrons 73 Ge(n,n',γ) Gammas Ionization threshold Fiducial volume(≈ 55%) Heat Ionization guard Ionization center Thermometer (Ge NTD) Reference electrode Center electrode Guard Electrodes Ge crystal Center electrode Guard ring 7 cm m=320g

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD data taking with heat trigger New data taking with trigger on heat signal Improved efficiency at low energy (50 % at 11 keV) Fiducial exposure: 22 kg.d Stable behavior over 4 months 18 nuclear recoil candidates > 15 keV Possible backgrounds Residual neutron flux 1 n-n coincidence observed 2 single expected by MC Surface electron recoils Miscollected charge events at low energy Not visible in coincidence events Further background studies

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 6 Final results of EDELWEISS-I (1) Final results: 62 kg.d (fid. exp.) 50% trigger efficiency at 15 keV 40 nuclear recoil candidates > 15 keV (only 3 with 30 <E R < 100 keV) Unknown background Used method developed by S. Yellin to derive exclusion limits (as CDMS) *(PRD 66, (2002)) No background subtraction V.Sanglard et al., PRD 71, (2005) Experiment stopped in March 2004

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 7 Exclusion limit – Spin Independent EDELWEISS starts to explore some optimistic SUSY models Best sensitivity : 1.5x GeV/c² Need a gain in sensitivity of a factor 100 – (EDW-II, EURECA) This gain depends on improvements On background discrimination On mass

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 8 Exclusion limit – Spin Dependent 7.8 % of 73 Ge (J=9/2) in natural Ge Spin on neutron or proton results present in (a p, a n ) diagram a p, a n = effective coupling between WIMP and proton, neutron For each WIMP mass, the constraint is Optimisitic SUSY models are a factor 100 below Direct detection experiments not yet competitive with indirect detection (SK)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 9  -ray background in EDELWEISS-I Before nuclear recoil selection, rate in detectors is ~1.5 event/kg/day/keV at low energy At high energy, spectrum shape and rate consistent with simulations of the measured U/Th contamination in the bulk of the Cu shielding Room for improvement in EDELWEISS-II, where this Cu is not used

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 10 Neutron background in EDELWEISS-I Measurement of the neutron flux with E >1 MeV : 1.1  0.1(stat) n/cm²/s Good understanding of neutron propagation in the setup (agreement between simulated and experimental spectrum) Determination of single rate : ~2 nuclear recoil expected in 62 kg.d (ambient radioactivity + U contamination of copper and lead) 1 n-n coincidence observed in 62 kg.d Not a strong constraint on the single neutron rate in the data Expected ratio double/single ~1/10 1 n-n  1 – 40 single with E R >15 90% C.L. Indistinguishable from the miscollected events in the nuclear recoil band

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 11 Surface backgrounds in EDELWEISS-I 1 E = 5.3 MeV, Q = 0.3 Peak at E=5.3 MeV  ’s from 210 Po? Q=0.3   decays near surfaces Rate ~ 400 /m²/j As expected, non-fiducial part more exposed to  flux Very likely due to 210 Pb on Cu or Ge surfaces No 206 Pb recoil peak at 100 keV observed as heat-only events : 210 Pb implanted in Cu, not Ge. Rate of 0.3<Q<1.0 events at low energy consistent with surface  ’s expected in 210 Pb hypothesis (but does not exclude possible contribution from 14 C) By removing Cu covers between detectors Possible gain Better identification by coincidences

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 12 EDELWEISS-II in few words Installation in the LSM started summer rst funded stage : 28 detectors 21*320g optimized Ge/NTD detectors and holders 7*400g Ge/NbSi detectors with active surface events rejections First cryogenic test with bolometers jan 2006 Commissioning run with 8 bolometers New electronic and acquisition systems: square modulation, continuous digitization close to the readout, optical fibers and numerical trigger Goal *100 in sensitivity :  w-n  pb evt/kg/day (E R >10keV)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 13 EDELWEISS-II improvements – Cryostat Reversed geometry Nitrogen free : 3 Pulse tube (50K and 80K screens) and 1 He cold vapor reliquefier (consumption  0) Large volume 50l  Self shielding Up to  120 detectors  More statistics Compact and hexagonal arrangement  More coincidence (n bkg)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 14 EDELWEISS-II improvements – Backgrounds Radiopurity Dedicated HPGe detectors for Systematic checks off all materials Clean Room (class 100 around the cryostat, class for the full shielding Deradonized air (from NEMO3) (0.1 Bq/kg) 20 cm Pb shielding Neutron Shielding EDW-I : 30cm paraffin EDW-II : 50 cm PE and better coverage µ veto (99% coverage)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 15 EDELWEISS-II improvements – Ge/NTD detectors Developed by CEA Saclay and Camberra-Eurisys Amorphous Ge and Si sublayer (better charge collection for surface events) Optimized NTD size and homogeneous working T ( mK) : sub keV resolution New holder and connectors (Teflon and copper only)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 16 EDELWEISS-II improvements – surface events Important limitation to the sensitivity : due to trapping and recombination, surface events are miscollected and can mimic nuclear recoils 2 approaches : Passive rejection : improve the charge collection for surface event Physics of the charge collection, trapping, surface charge, regeneration Physics of the Ge and Si amorphous sublayer Detectors with thick electrodes Active rejection : identification of the surface events Pulse shape analysis of the charge signals (but high bandwidth  low noise)  localization of the event Interdigitzed electrodes Detectors sensitive to athermal phonons  Ge/NbSi detectors

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 17 Identification of surface events with Ge/NbSi detector Identification of near surface events using athermal phonon measurement with NbSi thin film thermometers Heat and ionization Ge detectors Enhancement of athermal signals for near surface events Thermal signals proportionnal to the deposited energy Before rejection After rejection (1mm cut) Improvement of a factor 20 Fiducial volume reduction of 10 %

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 18 EDELWEISS-II present status 8 bolometers : 2*320g Ge/NTD with EDW-I holder 2*320g Ge/NTD with EDW-II holder and teflon clamp 2*320g Ge/NTD with EDW-II holder and Cu springs 1*IAS 50g heat and light detector (Al 2 O 3 ) 1*200g Ge/NbSi Goals : Validation of the microphonics (pulse tube decoupling system), new holders and new comb connectors for Ge/ntd, new electronics scheme, new acquisition system…

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 19 EDELWEISS-II future Feb-march 2006 : present run =commissioning April 2006 : EDELWEISS-II 28 detectors (21 Ge/NTD and 7 Ge/NbSi) + IAS detector (heat and light) 2006 : Approval of the 2 nd stage : 120 detectors In term of sensibility : EDELWEISS-II : 1 evt/kg/year EURECA : 10 evt/kg/an

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 20 Surface effects in charge collection Miscollected charge events can simulate nuclear recoils Use of gamma calibration ( 57 Co, 137 Cs) to check the charge collection Few miscollected charge events with amorphous layer Since 2002 use detectors with amorphous layer in Ge or Si WITH WITHOUT

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 21 EDELWEISS-II experimental setup Structure : 10 tons Pb shield : 35 tons PE shield : 35 tons

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 22 EDELWEISS-II improvements – Cryostat control  Cryostat fully controlled by automate  slow control data common with the data acquisition system (P, T, cRd, etc.)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 23 EDELWEISS-II improvements – Electronics Bolometer Boxes developed by CEA and IN2P3, plugged directly on the cryostat Heat modulation and charge bias by programmable DACs Continuous 200 kHz digitization, output by optical fibers Filtering, demodulation and trigger by soft in the acquisition system Numeric (DACs and ADCs Heat amplifier Charge amplifiers Alimentation To the cryostat (cold electronics and Bolometers) Outputs

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 24 Conclusion Hard competition to confirm SUSY at LHC CDMS-II, CRESST-II, EDELWEISS-II, XENON, XMASS sensitivity goals (~few event/ton/day) 1 Ton sensitivity goal (~few event/ton/year) CDMS, CRESST EDELWEISS-I present (~0.1 event/kg/day) L. Rozkowski et al., hep-ph/

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 25 EDELWEISS-I runs Trigger on ionization signal RunDetectorExposure (kg.d) 2000GeAl GGA i GSA3 GSA1 GGA p GSA3 GSA1 GGA Trigger on heat signal Total fiducial exposition : 62 kg.d

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 26 EDELWEISS-2 active  Veto VETO =100 m 2 of plastic scintillator (42 modules) shielding concept: 20cm Pb (36 tons) 50cm PE (30 tons) 5cm active  veto PM 2“ XP 2262 (Photonis)

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 27 µ veto installation in LSM cryopumps & lines µ veto on PE lower south wall upper east wall one of 6 reversed U´s completion of upper µ veto installation of the µ veto system

Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 28 EDELWEISS-2 µ veto simulations & first data  ~1.3kHz t ~ 300h implemented geometry for GEANT4 simulations of µ DIS µ test data: 120mV individ.thr.   mod.end ~ 1.3kHz  µ ~ mHz for total µ veto system