A Search for Cold Dark Matter with Cryogenic Detectors at Frejus Underground Laboratory * EDELWEISS experiment 1.Experiment status and results for first 3 years 2. Further plans 3. JINR participation E. Yakushev 30 th meeting of Program Advisory Committee for Nuclear Physics June 2009 E. Yakushev 30 th meeting of Program Advisory Committee for Nuclear Physics June 2009 *Expérience pour DEtecter Les WIMPs En Site Souterrain (Underground experiment to detect WIMPs) CEA Saclay (France) CSNSM Orsay (France) IPN Lyon (France) Institut Néel Grenoble (France) FZ/ Universität Karlsruhe (Germany) JINR Dubna JINR group: V. Brudanin, A. Belozub, A. Lubashevskiy, D. Filosofov, Yu. Gurov, L. Perevoshchikov, S. Rozov, E. Shevchik, S. Semikh, E. Yakushev (average age is 35 years)

Heat measurements Ionization measurements Q=E ionization /E recoil  Q=1 for electronic recoil  Q  0.3 nuclear recoil  Event by event identification of the recoil  Discrimination  /n > 99.99% for E r > 15keV Q=E ionization /E recoil  Q=1 for electronic recoil  Q  0.3 nuclear recoil  Event by event identification of the recoil  Discrimination  /n > 99.99% for E r > 15keV 2 remaining problems: - Neutrons - Surface electrons (miss collected charge) 2 remaining problems: - Neutrons - Surface electrons (miss collected charge) Basis for EDELWEISS experiment is Heat and Ionization Ge detectors Calibration AmBe Recoil energy (keV) Ionization/Recoil Ratio

EDELWEISS2 setup Cryogenic installation (20 mK) –Reversed geometry cryostat –Dilution refrigerator + pulse tube –Room for up to 40 kg of detectors Shielding –Clean room + deradonized air –20 cm Pb –50 cm PE –Active  veto Facilities –Remotely controlled sources for calibrations and regenerations –Remote operations (cryogeny, acquisition, …) –Detector storage and repair within the clean room Location –Laboratoire Souterrain de Modane (LSM) in the Frejus highway tunnel connecting France and Italy. –1800 m of rock overburden (~4800 mwe), muon flux 10 6 times less and neutron flux 10 4 times less than at see level.

EDELWEISS-II Detectors Surface events Radial coordinate (cm) Z (cm) guard electrode G : + 1V guard electrode H : - 1V A electrodes : + 2V B electrodes 0V C electrodes : - 2V D electrodes : 0V Electrons trajectories holes trajectories A & C Bulk event A, B & C Event in low-field area A & B Near surface event EDELWEISS now: 23 “standard” Ge/NTD bolometers 10 “Interdigit” bolometers ~ 10 kg of Ge “standard” Ge/NTD bolometers (320 g) Classical Ge detector with small NTD detector (Neutron Transmutation Doped Ge thermistances) for measurements of  K temperature changes. “interdigit” Ge/NTD bolometers ( g) Central electrode changed to ring electrodes, that provides active surface rejection

210 Pb source calibration at LSM Rejection ~ 1 in ! Equivalent to exposure of kgd ! Gamma rejection better than 1 in 10 5 Expected background 0.1 per 3000 kg.d ID detectors and results 210 Pb  rejection of 200g -equivalent to 3x10 4 kgd 6x Bi 6x Po

Energy thresholds in heat and ionization channels are < 2 keV

Sensitivity of “standard” NTD detectors is limited by surface background events In 93 kgd accumulated during few months in 2008, 3 background events, ~ 5.0 *10 -7 pb

Up to 35x320g Ge will be reprocessed (10 kg) Possibility to accumulate up to 3000 kgd background free data in next 3 years. Potential for exploring 4x10 -9 pb level for SI WIMP-nucleon cross section (region of interest of SUSY models – discovery of WIMPs) Further plans

FID 401: (1.5 x 5 x 1)mm 3 NTD R&D on ~2 times more efficient FID detectors

10 -7 pb pb Xenon 10 CDMS ExperimentExposure kg.dExpected evts in ROIObserved evtsWhen Performed CDMS - Ge Xenon10 - Xe13610 ZEPLIN III -Xe Running/prep Xenon100 - Xe3000 to (simu)2009 CDMS –Ge200additional ???2009 Edelweiss - Ge (calib)2011 Best limits for direct WIMP search obtained by different technologies Best limits for direct WIMP search obtained by different technologies

Contribution of JINR 1) Assembly, commissioning (calibrations, tests, etc) 2) Background environment control (radon and neutron) and material’s selection 3) Direct beta calibrations, MC and interpretation 4) Data analysis

During WIMP data taking almost all time radon level is below 0.1 Bq/m 3 Periods if high radon level are known and will be not taken in the final WIMP analysis Main source of high radon level – power outages in the lab followed by stops of anti-radon factory Contribution of JINR / Control of radon level at cryostat environment Continuous control of radon level at cryostat proximity with build at JINR high sensitive (mBq/m 3 level) radon detector

Radon detector as excellent instrument for control of shields AmBe installed AmBe taken out Small problem with anti-radon factory Few mm gap between shields June 3-5, 2009 Few mm gap between shields June 3-5, 2009 We have good instrument to check if 2 parts of shields are in touch, → Extremely important for correct interpretation of results

Contribution of JINR / Measurement and monitoring of neutron flux at LSM Measurement of neutron flux inside of EDELWEISS shields: Achieved level < n/cm 2 /sec (90% CL) Measurement and continuous monitoring of fast and thermal neutrons with 3 He based detectors (plus moderator for fast neutrons) Main challenge – flux is low (low background counters were used 150 cpd / background <1 cpd) Influence of position of neutron shield on surrounding neutron field Detector of thermal neutrons Detector of fast neutrons 4 3 He proportional counters inside PE moderator

Conclusion and outlook EDELWEISS-2 setup is fully operational + Improved background understanding and significant reduction of backgrounds with respect to EDELWEISS-1 + Resolutions OK + Magic point (background rejection 99.99%) at 15 keV + Surface rejection ok for 3000 kgd background free : above 200 kg.d fiducial exposure with 15 keV threshold and with detectors with active surface rejection (sensitivity 4x10 -8 pb). This will be world leading result received with background free data!!! + Up to 35x320g Ge will be reprocessed + Potential for exploring 4x10 -9 pb level in next few years (region of interest of SUSY models – discovery of WIMPs) JINR contribution is highly valuable at EDELWEISS collaboration

Contribution of JINR /Direct beta calibrations, surface events study Our JINR group performed MC studies dedicated to interpretation of background caused by 210 Pb trace contamination of detectors’ surfaces. Advantage EDELWEISS: direct beta calibration with 210 Pb source is available Result: Using experimental information about number of detected a from 210 Po decay we were able to explain nature of background events in low-energy region including nuclear recoil band. This become key information on interpretation of detected background at “standard” NTD detectors.

Fréjus safety tunnel (LSM) extension: approved! # To probe 10 −10 pb; # 1 tonne Cryo detector; # ~10 -5 evts / (kg day) Part of ILIAS/ASPERA European Roadmap 68% Ruiz de Austri, Trotta & Roszkowski (2006) CDMS 95% Far perspective (after few years) EURECA – 1t multi target project collaboration between EDELWEISS and CREST (CaWO 4 ) Far perspective (after few years) EURECA – 1t multi target project collaboration between EDELWEISS and CREST (CaWO 4 )

~2003 ~2007 Near Future Theoretical Predictions Baer, Balazs, Belyaev, O’Farrill hep-ph/ Bulk Focus Point Stau coannih LHC Evt/kg/d Evt/kg/y Evt/t/y

Magic point (reduction factor 10 3 and better) at 20 keV for almost all detectors Results from “standard” NTD detectors Significant reduction of background with respect to EDELWEISS-I Ionization/Recoil Ratio Recoil energy (KeV) Almost continuous data taking from January 2006 / Commissioning runs at WIMP data taking at 2008 In total 10 cool-downs since January 2006 (2-4 month each)

The Universe is very different and much more interesting than we expected Astrophysical data clearly shows existence of an unidentified form of matter Dark matter can be directly detected if consist from WIMPs SUSY has an excellent candidate: neutralino Subject for study Basis for all direct search of WIMPs at Earth experiments According to models of cosmological structure formation, the luminous matter of galaxies is gravitationally bound to a more massive halo of Dark Matter. →Thus, ordinary matter is moving through Dark Matter halo (We around Galactic Centre) and Dark Matter particles have kinetic energy in our laboratory system. → WIMP can be detected by it elastic scattering off nuclei. Expected rates and deposited energy are low, special methods required for experimental search The EDELWEISS is one of experiments for direct search of dark matter in forms of WIMPs

Almost continuous data taking from January 2006 / Commissioning runs at WIMP data taking at 2008 In total 10 cool-downs since January 2006 (2-4 month each)