Physics at Extreme Energies, Hanoi, July 2000 Dark Matter Search in the EDELWEISS expt G. Chardin DAPNIA/SPP, CEA-Saclay

Physics at Extreme Energies, Hanoi, July 2000 EDELWEISS Collaboration CEA-Saclay DAPNIA: G. Chardin, M. Gros, A. Juillard, A. de Lesquen, M. Loidl, J. Mallet, L. Miramonti, L. Mosca, X-F. Navick CEA-Saclay DAPNIA: G. Chardin, M. Gros, A. Juillard, A. de Lesquen, M. Loidl, J. Mallet, L. Miramonti, L. Mosca, X-F. Navick CEA-Saclay DRECAM: M. Chapellier, P. Pari CEA-Saclay DRECAM: M. Chapellier, P. Pari CRTBT Grenoble: A. Benoit, M. Caussignac CRTBT Grenoble: A. Benoit, M. Caussignac CSNSM Orsay: L. Bergé, A. Broniatowski, L. Dumoulin, A. Juilliard, S. Marnieros, N. Mirabolfathi CSNSM Orsay: L. Bergé, A. Broniatowski, L. Dumoulin, A. Juilliard, S. Marnieros, N. Mirabolfathi IAP Paris: C. Goldbach, G. Nollez IAP Paris: C. Goldbach, G. Nollez IPN Lyon: B. Chambon, M. De Jesus, D. Drain, J. Gascon, J-P. Hadjout, O. Martineau, C. Pastor, E. Simon, M. Stern IPN Lyon: B. Chambon, M. De Jesus, D. Drain, J. Gascon, J-P. Hadjout, O. Martineau, C. Pastor, E. Simon, M. Stern Fréjus Underground Lab: Ph. Charvin Fréjus Underground Lab: Ph. Charvin

Physics at Extreme Energies, Hanoi, July 2000 EDELWEISS Dark Matter Search Introduction Introduction Limitations of present experiments Limitations of present experiments Cryogenic double detection detectors Cryogenic double detection detectors First 70 g germanium detectors: discrimination performances First 70 g germanium detectors: discrimination performances Anomalous NaI events Anomalous NaI events Second generation 70 g detectors Second generation 70 g detectors Present stage: 3 x 320 g Ge detectors Present stage: 3 x 320 g Ge detectors First results and expected sensitivity First results and expected sensitivity The EDELWEISS-II experiment The EDELWEISS-II experiment Perspectives and conclusions Perspectives and conclusions

Physics at Extreme Energies, Hanoi, July 2000 WIMPs direct detection: (some) conventional and cryogenic experiments ELEGANT, LiF CDMS EDELWEISS CRESST, HDMS, DAMA Gran Sasso AMANDA (indirect) ANTARES(indirect) UKDMC EDELWEISS: Fréjus underground lab CRESST Al 2 O 3 Gran Sasso CRESST Al 2 O 3 Gran Sasso EDELWEISS Fréjus) EDELWEISS Fréjus) Canfranc Milano/Genova/Napoli/ (Te0 2 Gran Sasso Canfranc Milano/Genova/Napoli/ (Te0 2 Gran Sasso CDMS (Ge and Si, Berkeley/Stanford) CDMS (Ge and Si, Berkeley/Stanford) DAMA (NaI, Gran Sasso) UKDMC Boulby Mine) DAMA (NaI, Gran Sasso) UKDMC Boulby Mine) ELEGANT, ELEGANT, ROSEBUD

Physics at Extreme Energies, Hanoi, July 2000 The Fréjus Underground Laboratory Muon flux ≈ 4 muons/m 2 /day Muon flux ≈ 4 muons/m 2 /day Neutron flux (mainly from rock) ≈ s -1 cm -2 Neutron flux (mainly from rock) ≈ s -1 cm -2

Physics at Extreme Energies, Hanoi, July 2000 EDELWEISS WIMP search Measure charge and heat signal to separate : Measure charge and heat signal to separate : electron recoils (  background)electron recoils (  background) nuclear recoils (neutrons, WIMPs…)nuclear recoils (neutrons, WIMPs…)

Physics at Extreme Energies, Hanoi, July 2000 EDELWEISS WIMP search Physics data takings: Not two, but four populations observed (nuclear and electron recoils, volume and surface events) Physics data takings: Not two, but four populations observed (nuclear and electron recoils, volume and surface events)

Physics at Extreme Energies, Hanoi, July 2000 Unexpected events… Anomalous events in UKDMC and Saclay NaI experiments (not reported by DAMA): events almost like nuclear recoils but faster… Anomalous events in UKDMC and Saclay NaI experiments (not reported by DAMA): events almost like nuclear recoils but faster… EDELWEISS example: not two, but four categories of events EDELWEISS example: not two, but four categories of events Surface nuclear recoils: A. Benoit et al., Phys. Lett. B 479 (2000) 8 Surface nuclear recoils: A. Benoit et al., Phys. Lett. B 479 (2000) 8 Surface events probably represent the main limitation of NaI, classical germanium (e.g. HDMS, GENINO) and cryogenic germanium experiments Surface events probably represent the main limitation of NaI, classical germanium (e.g. HDMS, GENINO) and cryogenic germanium experiments

Physics at Extreme Energies, Hanoi, July 2000 Anomalous events in NaI experiments Tails on the time distribution of NaI events: Events faster than nuclear recoils Tails on the time distribution of NaI events: Events faster than nuclear recoils Rate: few evts/kg/keV/day Rate: few evts/kg/keV/day Total number < Nb of alpha events Total number < Nb of alpha events Smith and Spooner, Phys. World Jan. 2000

Physics at Extreme Energies, Hanoi, July 2000 Low energy surface nuclear recoils Consider for example the  - decay of 210 Po  206 Pb +  due to a pollution at the detector surface: Consider for example the  - decay of 210 Po  206 Pb +  due to a pollution at the detector surface: For a total released energy of 5 MeV, ≈4.9 MeV will be carried away by the  particle and ≈100 keV by the 206 Pb nucleus. For a total released energy of 5 MeV, ≈4.9 MeV will be carried away by the  particle and ≈100 keV by the 206 Pb nucleus.

Physics at Extreme Energies, Hanoi, July 2000 Anomalous NaI events: surface nuclear recoils ? Surface nuclear recoils will give events in the 5-10 keV range (since quenching factor <0.1) Surface nuclear recoils will give events in the 5-10 keV range (since quenching factor <0.1) Heavy nuclei at low energy and on surface: scintillation decay times expected to be faster than nuclear Na or I recoils, or alphas (see UKDMC and Saclay publications) Heavy nuclei at low energy and on surface: scintillation decay times expected to be faster than nuclear Na or I recoils, or alphas (see UKDMC and Saclay publications) Note: energy observed in detector will depend strongly on state of detector surface (very flat surface : apparent energy 5-10 keV, rougher surface :  energy loss in addition possible) Note: energy observed in detector will depend strongly on state of detector surface (very flat surface : apparent energy 5-10 keV, rougher surface :  energy loss in addition possible) Event rate appears compatible with  event rate (up to trigger effects, should be the same as surface alphas) Event rate appears compatible with  event rate (up to trigger effects, should be the same as surface alphas)

Physics at Extreme Energies, Hanoi, July 2000 Anomalous events: Consequences Discrimination analysis: statistical discrimination (distributions overlapping) requires that all populations be identified (fit with 2 degrees of freedom ≠ 4 d.o.f) Discrimination analysis: statistical discrimination (distributions overlapping) requires that all populations be identified (fit with 2 degrees of freedom ≠ 4 d.o.f) Necessary to include additional degrees of freedom of surface electron recoils (cf. Saclay) and surface nuclear recoils (for NaI + all discrimination expts) Necessary to include additional degrees of freedom of surface electron recoils (cf. Saclay) and surface nuclear recoils (for NaI + all discrimination expts) Expected to play a significant role in spin-dependent analysis (marginally for coherent coupling) (factor ≈10) Expected to play a significant role in spin-dependent analysis (marginally for coherent coupling) (factor ≈10) Note: even if population is not seen, it should be included in the fit (if surface state is excellent, visible energy will be 5-10 keV in NaI crystals) Note: even if population is not seen, it should be included in the fit (if surface state is excellent, visible energy will be 5-10 keV in NaI crystals)

Physics at Extreme Energies, Hanoi, July 2000 Anomalous events: Consequences (ff) Important to study in detail surface events for charge detectors, and also for scintillation detectors Important to study in detail surface events for charge detectors, and also for scintillation detectors Further study to confirm our hypothesis: analysis of coincident data taken with Ge-4 and Ge-5 detectors (but saturation and non linearity of heat channel) Further study to confirm our hypothesis: analysis of coincident data taken with Ge-4 and Ge-5 detectors (but saturation and non linearity of heat channel) Hypothesis can be tested on a NaI crystal by using an implanted source (Po or Rn, e.g., cf. Milano group Hypothesis can be tested on a NaI crystal by using an implanted source (Po or Rn, e.g., cf. Milano group Events present in DAMA ? (same crystals as Saclay), discrimination factors taking into account additional population ? Events present in DAMA ? (same crystals as Saclay), discrimination factors taking into account additional population ?

Physics at Extreme Energies, Hanoi, July 2000 The DAMA claim Detected not by direct observation, but by searching for an annual modulation effect (≈10 5 events if correct) Detected not by direct observation, but by searching for an annual modulation effect (≈10 5 events if correct)

Physics at Extreme Energies, Hanoi, July nd generation 70g germanium bolometers Improved radioactive environment Improved radioactive environment Close roman lead shield Close roman lead shield Removable paraffin shielding (30 cm thick) Removable paraffin shielding (30 cm thick) Acoustic isolation improved Acoustic isolation improved Nitrogen flushing against radon Nitrogen flushing against radon New implantation schemes for the electrodes New implantation schemes for the electrodes

Physics at Extreme Energies, Hanoi, July g Ge detectors of the "1 kg" stage of EDELWEISS-I

Physics at Extreme Energies, Hanoi, July g Ge detectors of the "1 kg" stage of EDELWEISS-I Three 320 g Ge detectors Three 320 g Ge detectors Close spacing, guard ring for middle detector Close spacing, guard ring for middle detector Improved radioactive environment Improved radioactive environment

Physics at Extreme Energies, Hanoi, July 2000 "1 kg" stage of EDELWEISS-I: first results Very preliminary data from first 320 g detector Very preliminary data from first 320 g detector Still a factor ≈ 5 from CDMS and DAMA benchmarks, but resolution can be significantly improved and new detector with guard ring + germanium protection starting to be operated Still a factor ≈ 5 from CDMS and DAMA benchmarks, but resolution can be significantly improved and new detector with guard ring + germanium protection starting to be operated

Physics at Extreme Energies, Hanoi, July 2000 Reaching SUSY models

Physics at Extreme Energies, Hanoi, July 2000 EDELWEISS: R&D to get rid of surface events Discrimination performances of charge + heat detectors are excellent, but surface events are uncomfortably close to nuclear recoil band Discrimination performances of charge + heat detectors are excellent, but surface events are uncomfortably close to nuclear recoil band To remove surface events: To remove surface events: record risetime structure of charge signal (A. Broniatowski et al.)record risetime structure of charge signal (A. Broniatowski et al.) detect out-of-equilibrium phonons and fast vs. slow component ratiodetect out-of-equilibrium phonons and fast vs. slow component ratio lower charge energy threshold and improve energy resolution (AsGa FETs, Single Electron Transistor)lower charge energy threshold and improve energy resolution (AsGa FETs, Single Electron Transistor)

Physics at Extreme Energies, Hanoi, July 2000 Remove surface events (ff) Large NbSi film sensors efficiently collect out-of- equilibrium phonons (« fast » component) Large NbSi film sensors efficiently collect out-of- equilibrium phonons (« fast » component) Fast/slow component ratio depends on location of energy deposition Fast/slow component ratio depends on location of energy deposition Sensor 1 Sensor 2 Radioactive source

Physics at Extreme Energies, Hanoi, July 2000 Remove surface events (ff) Record risetime structure of charge signal (A. Broniatowski et al. LTD8 conf. proc.) Record risetime structure of charge signal (A. Broniatowski et al. LTD8 conf. proc.) Cut on risetime is able to remove electron events at 60 keV Cut on risetime is able to remove electron events at 60 keV Pb: reach the <≈10 keV level Pb: reach the <≈10 keV level

Physics at Extreme Energies, Hanoi, July 2000 Decrease charge threshold using the Single Electron Transistor Charge manipulation in the quantum regime Charge manipulation in the quantum regime Ultra small capacitances now achievable ≈ 1 fF ( F) Ultra small capacitances now achievable ≈ 1 fF ( F) Coulomb blockade: when 1 electron present, other electrons must wait outside Coulomb blockade: when 1 electron present, other electrons must wait outside 3-4 orders of magnitude increase in charge sensitivity over best FET-based devices if capacitance is adapted 3-4 orders of magnitude increase in charge sensitivity over best FET-based devices if capacitance is adapted Dual of the SQUID system Dual of the SQUID system

Physics at Extreme Energies, Hanoi, July 2000 An SET-based Si photodetector Cleland et al. ( Appl. Phys. Lett. 61 (1992) 2820 ): proof of principle, coupling of a Si detector to a Single Electron Transistor circuit Cleland et al. ( Appl. Phys. Lett. 61 (1992) 2820 ): proof of principle, coupling of a Si detector to a Single Electron Transistor circuit

Physics at Extreme Energies, Hanoi, July 2000 Extending the bandwidth of the SET for charge detection Idea: move to high- frequencies Idea: move to high- frequencies Ex: couple the SET to a GHz resonant circuit and measure damping (Schoelkopf et al. Science 1998) Ex: couple the SET to a GHz resonant circuit and measure damping (Schoelkopf et al. Science 1998) Fantastic sensitivity: still-unoptimized device: ≈ e/√Hz Fantastic sensitivity: still-unoptimized device: ≈ e/√Hz Sensitive enough to feel a single particle Sensitive enough to feel a single particle Problem: capacitive coupling is difficult Problem: capacitive coupling is difficult EDELWEISS: realize a prototype with C ≈ 2 pF and ≈ 500 eV charge threshold EDELWEISS: realize a prototype with C ≈ 2 pF and ≈ 500 eV charge threshold

Physics at Extreme Energies, Hanoi, July 2000 EDELWEISS-II shielding Efficient protection against neutron Efficient protection against neutron and gamma-ray backgrounds Designed to improve by > 2 orders of Designed to improve by > 2 orders of magnitude the best present performances

Physics at Extreme Energies, Hanoi, July 2000 Innovative reversed cryostat (100 l) Large volume (100 l) Large volume (100 l) Efficient geometry Efficient geometry Innovative cryogenic solutions (pulsetubes, compact cryogenic system…) Innovative cryogenic solutions (pulsetubes, compact cryogenic system…) 10 mK base 10 mK basetemperature

Physics at Extreme Energies, Hanoi, July 2000 Conclusions EDELWEISS Dark Matter Search: now entering the allowed region of SUSY models EDELWEISS Dark Matter Search: now entering the allowed region of SUSY models The present "1 kg" stage should be able to test the whole DAMA region The present "1 kg" stage should be able to test the whole DAMA region Detector developments are pursued to: Detector developments are pursued to: get rid of surface eventsget rid of surface events lower charge energy thresholdlower charge energy threshold apply developments to other physics applications: coherent scattering, solar neutrinos, mass of antiproton…apply developments to other physics applications: coherent scattering, solar neutrinos, mass of antiproton… Testing most of SUSY parameter space will require > kg stage Testing most of SUSY parameter space will require > kg stage EDELWEISS is exploring with CRESST the best strategy for a cryogenic experiment at the 100 kg scale. EDELWEISS is exploring with CRESST the best strategy for a cryogenic experiment at the 100 kg scale.