The EDELWEISSII experiment Silvia SCORZA Universit Claude Bernard

The EDELWEISS-II experiment Silvia SCORZA Université Claude Bernard- Institut de Physique nucléaire de Lyon CEA-Saclay DAPNIA/DRECAM (FRANCE), CNRS/CRTBT Grenoble (FRANCE), CNRS/IN 2 P 3/CSNSM Orsay (FRANCE), CNRS/IN 2 P 3/IPN Lyon (FRANCE), CNRS/INSU/IAP Paris (FRANCE), CNRS-CEA/Laboratoire Souterrain de Modane (FRANCE), JINR Dubnia (RUSSIA), FZK/Universtat Karlsruhe (GERMANY)

Outline n Limits of EDELWEISS-I n n EDELWEISS-II setup Current situation (3 detector types) n Outlook

Direct Search Principle Detection of the energy deposited due to elastic scattering off target nuclei • Event Rate : < 1 ev /kg/week • Recoil Energy : 1 – 100 ke. V • Low energy threshold ◊ Large detector mass • Low background Radio – purity Active/passive shielding Deep underground sites

EDELWEISS @ Laboratoire Souterrain de Modane

Ge Heat-Ionization Detectors n n n => discrimination g/n > 99. 9% for Er>15 ke. V Simultaneous measurements: q Ionization @ few V/cm with Al electrodes q Heat @ 17 m. K with Ge/NTD sensor Different Ionization/Heat energy ratio for nuclear and electronic recoils (dominate bkg) Event by event background rejection

Edw-I limiting background PRD 71, 122002 (2005) Best Sensitivity up to 2003, but… Background in the physics data taking Leakage from the g to the recoil band Neutrons: - 1 n-n coincidence observed - Neutron shield not thick enough Surface electron recoils: - Bad charge collection (trapping and recombination) - Rate compatible with 210 Pb contamination: rate a “e-” 5/kg. day E=5. 3 Me. V Q=0. 3 210 Pb 210 Po b 206 Pb

EDW – II set-up radiopurity dedicated HPGe detectors for systematic checks of all materials clean room (class 100 around the cryostat, class 10000 for the full shielding) deradonized air (from NEMO-3) neutron shielding · 20 cm Pb shielding · 50 cm PE and better coverage active m veto (>98% coverage) up to 110 detectors · Ge/NTD + Ge/Nb. Si + new ID electrodes expected sensitivity: EDW-I × 100 sc-n 10 -8 pb (phase 100) = 0. 002 evts/kg/day (Er>10 ke. V)

Ge-NTD detectors 23*320 g Ge/NTD : Developed by CEA Saclay and Canberra-Eurisys Amorphous Ge and Si sublayer: better charge collection for surface evts Optimized NTD size and homogeneous working T (16 -18 m. K) : goal ke. V resolution New holder and connectors (Teflon and copper only) All @ LSM first low bg runs in 2006: old bg new bg EDW-I g rate: ~ 700 evts/kg/day for E>100 ke. V After the most recent improvement EDW-II g rate: ~ 300 evts/kg/day EDW-I rate on central electrode : 2. 5 - 5. 5 evts/kg/day (400 -1000 /m 2/day) EDW-II rate ~ 3 evts/kg/day

Ge/Nb. Si detectors identification of surface events with Ge/Nb. Si detector 7*400 g Ge/Nb. Si detectors : • developed by CSNSM Orsay • Nb. Si thin film thermometers for active surface evt rejection 2 @ LSM Thermometer Nb. Si A Thermometer Nb. Si B Heat signal of thermometer Surface event Bulk event 200 data taken with 1 Nb. Si detector May&June 2007: 1. 5 kg. d (fiducial) Nb. Si. A : 150 Transient 100 Thermal 50 0 0 20 40 60 -3 x 10 Time (ms) 80 Rejection works, resolutions needs tuning

ID detector ‘b’ electrodes: +1 V Z (cm) ‘a’ electrodes: +2 V ‘a&c’ bulk event ‘a&b’ nearsurface event guard ‘g’: + 1 V recoil energy [ke. V] Electron trajectories ‘a, b&c’ event in low-field area hole trajectories guard ‘h’: - 1 V ‘c’ electrodes: -2 V ‘d’ electrodes: -1 V after cut “b” < 5 ke. V (30% of evts. survive) all events Radius (cm) recoil energy [ke. V] lab data 200 g detector, concentric electrodes 2 mm gaps, 200µm width trigger thresh. 24 ke. V 241 Am source with 60 ke. V g´s

status ID bolometer summary: first detector (200 g) with interleaved electrodes in LSM Ø performance as expected New 400 g ID´s to be installed end of March ~1. 7 kg. d pr ry a n i m eli !

EDELWEISS-II next steps § Goal 2 x 10 -8 pb (1200 kg. d no event) (~1 evt/kg/y) § acquire physics data with 23 NTD § build 6 400 g Nb. Si §Goal 2 x 10 -10 pb (~10 evt/t/y) § build 16 Nb. Si (same/tuned if needed) § build 24 NTD with reduced contamination and/or with ID electrodes