EDELWEISSII Status and future Vronique SANGLARD CNRSIN 2

EDELWEISS-II : Status and future Véronique SANGLARD CNRS/IN 2 P 3/IPNLyon sanglard@ipnl. in 2 p 3. fr http: //edelweiss. in 2 p 3. fr Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD

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 2

The EDELWEISS Collaboration CEA-Saclay DAPNIA/DRECAM CNRS/CRTBT Grenoble CNRS/IN 2 P 3/CSNSM Orsay DUBNA (Russia) FZK/Univ. Karlsruhe (Deutschland) CNRS/INSU/IAP Paris CNRS/IN 2 P 3/IPN Lyon CNRS – CEA/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) Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 3

Heat and Ionization Ge detectors Thermometer (Ge NTD) Guard Electrodes Reference electrode Heat Guard ring Center electrode Fiducial volume(≈ 55%) Ge crystal Center electrode Simultaneous measurement of Heat @ 17 m. K with Ge/NTD sensor Ionization @ 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) EI/ER = 0. 3 for nuclear recoils EI/ER = 1 for electronic recoils Ionization guard Ionization center m=320 g 7 cm Ionization threshold Neutrons Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » 73 Ge(n, n', γ) Gammas Véronique SANGLARD 4

2003 data taking with heat trigger New data taking with trigger on heat signal Improved efficiency at low energy (50 % at 11 ke. V) Fiducial exposure: 22 kg. d Stable behavior over 4 months 18 nuclear recoil candidates > 15 ke. V 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 5

Final results of EDELWEISS-I (1) Final results: 62 kg. d (fid. exp. ) 50% trigger efficiency at 15 ke. V 40 nuclear recoil candidates > 15 ke. V (only 3 with 30 <ER< 100 ke. V) Unknown background Used method developed by S. Yellin to derive exclusion limits (as CDMS) *(PRD 66, 032005 (2002)) No background subtraction V. Sanglard et al. , PRD 71, 122002 (2005) Experiment stopped in March 2004 Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 6

Exclusion limit – Spin Independent EDELWEISS starts to explore some optimistic SUSY models Best sensitivity : 1. 5 x 10 -6 pb @ 80 Ge. V/c² Need a gain in sensitivity of a factor 100 – 10000 (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 7

Exclusion limit – Spin Dependent 7. 8 % of 73 Ge (J=9/2) in natural Ge Spin on neutron or proton results present in (ap, an) diagram ap, an = 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 8

g-ray background in EDELWEISS-I Before nuclear recoil selection, rate in detectors is ~1. 5 event/kg/day/ke. V 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 9

Neutron background in EDELWEISS-I Measurement of the neutron flux with E >1 Me. V : 1. 1 0. 1(stat) 10 -6 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 ER>15 ke. V @ 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 10

Surface backgrounds in EDELWEISS-I Peak at E=5. 3 Me. V a’s from 210 Po? Q=0. 3 a decays near surfaces Rate ~ 400 /m²/j As expected, non-fiducial part more exposed to a flux E = 5. 3 Me. V, Q = 0. 3 Very likely due to 210 Pb on Cu or Ge surfaces No 206 Pb recoil peak at 100 ke. V 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 b’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 1 Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 11

EDELWEISS-II in few words Installation in the LSM started summer 2004 1 rst funded stage : 28 detectors 21*320 g optimized Ge/NTD detectors and holders 7*400 g Ge/Nb. Si 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 10 -8 pb 0. 002 evt/kg/day (ER>10 ke. V) Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 12

EDELWEISS-II improvements – Cryostat Reversed geometry Nitrogen free : 3 Pulse tube (50 K and 80 K screens) and 1 He cold vapor reliquefier (consumption 0) Large volume 50 l 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 13

EDELWEISS-II improvements – Backgrounds Radiopurity Dedicated HPGe detectors for Systematic checks off all materials Clean Room (class 100 around the cryostat, class 10000 for the full shielding Deradonized air (from NEMO 3) (0. 1 Bq/kg) 20 cm Pb shielding Neutron Shielding EDW-I : 30 cm 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 14

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 (1618 m. K) : sub ke. V resolution New holder and connectors (Teflon and copper only) Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 15

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/Nb. Si detectors Dark Matter 2006 – Marina del Rey, California « EDELWEISS-II : Status and future » Véronique SANGLARD 16

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

EDELWEISS-II present status 8 bolometers : 2*320 g Ge/NTD with EDW-I holder 2*320 g Ge/NTD with EDW-II holder and teflon clamp 2*320 g Ge/NTD with EDW-II holder and Cu springs 1*IAS 50 g heat and light detector (Al 2 O 3) 1*200 g Ge/Nb. Si 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 18

EDELWEISS-II future Feb-march 2006 : present run =commissioning April 2006 : EDELWEISS-II 28 detectors (21 Ge/NTD and 7 Ge/Nb. Si) + 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 19