1. MACHe3: Prototype of a bolometric detector based on superfluid 3 He for the search of non-baryonic Dark Matter C. Winkelmann J. Elbs E. Collin Yu. Bunkov H. Godfrin E. Moulin J. Macias-Perez D. Santos MACHe3: (CRTBT / LPSC) MAtrix of Cells of superfluid Helium-3

2. Plan de l’exposé IMasse manquante de l’Univers et Matière Sombre non-baryonique II 3 He superfluide et thermométrie par Fil Vibrant aux ultra-basses températures III Détection bolométrique et calibration du détecteur IVSpectres de détection: neutrons, muons et électrons de basse énergie VPerspectives pour la recherche de Matière Sombre

3. Missing Mass and non-baryonic Dark Matter Flat Universe  ≈  c =5.1 GeV/m 3  r  m   ≈ 1.0 Energy density of matter in the Universe  M ≈ 1.6 GeV/m 3  m  ≈ 0.3   ≈ 0.7 Knop et al. (2003) Spergel et al. (2003) Allen et al. (2002)

4. Open questions in cosmology:  Presence of large scale structures imposes  baryons ≈ 0.2 - 0.3 GeV/m 3  Anomalies of galactic rotation curves Standard Cold Dark Matter Simulation VIRGO Vitesse de rotation (km/s) R 0 =8.5 kpc Honma et Sofue (1996) Rotation velocity km/s Measured Visible Matter contribution

5. Non-baryonic Dark Matter: W eakly I nteracting M assive P article s Supersymmetric extension of Standard Model provides a candidate: neutralino   stable (except annihilation)  relic density  massive (~ 100 GeV/c 2 )  Missing Mass  neutral in charge and color  Weak interaction cross section with ordinary matter Direct detection ~ Scalar interaction Edelweiss, CDMS,CRESST, Zeplin Ge, Si, CaWO 4, Xe Axial interaction DAMA/Libra, Picasso, Simple, MACHe3 NaI, F, 3 He

6. Project of bolometric detection based on 3 He Spin 1/2 nucleus  axial interaction with neutralino High transparency to  -rays Nuclear neutron capture reaction Limited recoil energy range: E recoil < 6 keV At ultra-low temperature (100 K, superfluid) Specific heat  exp(-/k B T) Absolute purity Liquid 3 He but: expensive, technologically challenging, …

7. CDMS 2004 preliminary MACHe3 Project: Potential of a bolometric detector involving 10 kg / 1000 cells  reduction of neutron, muon and  ray background  (Mayet et al., NIMA 2000). Preliminary analysis by simulation (LPSC) Mayet et al., PLB 2002

8. Vibrating wire thermometry at ultra-low temperatures

9. 3 He superfluide fermion: (2p + n) + 2e - A T c ~ 1 - 2.5 mK  Transition superfluide (onde-p)  Phases multiples  Phase B isotrope, de type BCS  (k)=   excitations: quasiparticules n qp exp(-/k B T) fraction superfluide + fraction normale vide renormaliségaz dilué de quasiparticules liquide jusqu’à T=0 (p <34 bars) EFEF T<<T c 

10. The Vibrating Wire Resonator H I 0 e i  t Induced voltage V 3 mm NbTi Monofilament (4.5 m) (Photo E. Collin) V (  V)

11. Hydrodynamics and slip  Fermi liquid 3 He liquide: T -2 hydrodynamic analysis (Stokes; Carless et al., JLTP 1983)  At low temperatures: corrections for finite viscous mean free path   Slip effect (Højgaard Jensen et al., JLTP 1980)  In the superfluid: Andreev scattering of quasiparticles on surfaces  « Quantum » slip (Einzel et al., PRL 1984; Fisher et al., PRL 1989) x   (x)  bulk /3 wallbulk Superfluid gap

12.  (T)/  (Tc) (21 bars) Ono et al., JLTP 1982 Towards a temperature standard < mK: Effective viscosity and thermometry CW et al., JLTP (2004)  Temperature calibration / platinum NMR  Extraction of an effective viscosity  eff (p,T)  appliable to other VWRs Ta, 125  m

13. Amortissement Fil Vibrant  n qp  pFpF -p F E p 0 1234 kBTkBT quasi-particule (v g.p>0) quasi-trou (v g.p<0) Relation de dispersion BCS vgvg Gaz balistique de quasiparticules v << v g

14. Ballistic quasiparticle gas  +p F v -p F v pFpF -p F E p 0 1234 Doppler shift of dispersion curves selective scattering of quasiparticles (Andreev scattering) (Fisher et al., PRL 1989) Non-linear damping v rms (mm/s) Excitation force (pN)

15. Bolometric detection and calibration A B C H Stycast sealing Copper support connected to silver sinters Gold sheet with 57 Co Copper sheet (25  m) Orifice for thermali- sation (200  m ) 15 mm 6 mm 3-cell bolometer VWRs (4.5 et 13  m)

16. Response to an instantaneous heat release A Response time of the thermometer Dynamical response of the thermometer W ret (Hz) Thermal equilibrium time Relaxation time of the bolometer Instantaneous heat release time (s)

17. Bolometric calibration coefficient Specific heat of quasiparticle gas Vibrating Wire damping Calibration coefficient We neglect - Adsorbed layers - Gap reduction close to surfaces - Bosonic modes of condensate  non-exponential dependence of U on T Non-linear dependence of W on velocity  (T,v) +

18. C (j/K) T (mK) C qp C ABS (Halperin) 1 0.40.15 W (Hz) Heat capacities 50.01 C add (Greywall)

19. Bolometric calibration by pulsed heating Energy injection by heater-VWR  linear dependence H(U puls ) Bradley et al., PRL 1995; Bäuerle et al., PRB 1998 Intrinsic losses in heater  Lost energy fraction Amplitude (a.u.) W mes (Hz) H I V heater thermometer time (s)

20.  1/√T Bolometric calibration by pulsed heating

21. Detection spectra: neutrons, muons and low energy electrons Comparison to known energy sources Characterization of the detector for different types of interaction - ionizing interaction (electron recoil): predominant for light and charged particles (rays, electrons, muons) - non-ionizing interaction (nuclear recoil): important for massive and neutral particles (WIMP, elastic neutron scattering) Ionization, secondary electrons  excited atomic and molecular states - heat - ultraviolet scintillation

22. Heat Ionization/scintillation Discrimination of electron recoils Electron recoil Nuclear recoil

23. Neutrons nuclear neutron capture Elastic diffusion m 3He ≈ m n  fast thermalisation of neutrons fast neutron thermalisation and nuclear capture :  good neutron background discrimination

24. Detection spectrum at W base =0.7 Hz Coups good agreement with description of detector Heat deposition : ( Bäuerle et al., Nature 1995) Energy deficit of 15 % - Scintillation ? - Topological defects ? p=0 bar Neutrons 70  m10  m 1  m p 3H-3H- Meyer, Sloan, JLTP 1998 Moderated AmBe source

25. Low energy electrons Radioactive decay Source is in situ (cell B) 10 100 1 E (keV) 57 Co emission Pile-up Electrons produced in gold sheet 136122 Moulin et al., to appear  rays Internal conversion electrons Auger electrons 14.4 13.6 7.3 5.50.6 21.727.9

26. Detection of low energy electrons from 57 Co Detection threshold and resolution at keV level  Expected energy range of neutralino signal reached W mes (mHz) time (s)

27. cell A (without source) cell B (with source) Electron detection spectrum resolution of low energy emission spectrum of 57 Co Comparison to 14 keV peak with bolometric calibration  Energy deficit of f UV (e -,14keV)≈265% UV Scintillation Energy dependence of scintillated fraction? f UV (e - >100keV)≈50% (McKinsey et al., NIMA 2002) S/B>5 Analysis LPSC, d5, B=100 mT, W0=430 mHz

28. Cosmic muons Cosmic muon flux: Surface 150 / m 2.s Underground (Gran Sasso) 2.310 -4 / m 2.s Large cross section (100 barns)  linear energy deposition (ionisation) dE/dx=1.9[g/cm3]MeV/cm Expected energy deposition in bolometers ~ 70 keV Coincident detection across cells coincidence W mes (Hz) time (s)

29. Analysis and simulation LPSC (GEANT4) Detection of cosmic muons: good agreement experience/simulation if f UV (muons) ≈ 25 %

30. rays (- 3 He) < 1-2 barn (diffusion Compton) << high-Z materials (photoelectric effect) Difficulty of a characterization by external source (Bradley et al., PRL 1995) 57 Co source: emission at 122 and 136 keV  no Compton edge in detection specta cell A (without source) cell B (with source) Analysis LPSC

31. Outlook for Dark Matter search Detector project (Mayet et al., NIMA 2002) 10 3 cells of 5 3 cm 3 10 kg 3 He target material Underground laboratory 5 cm

32. Parallel detection of scintillation Moulin et al., IVth. Int. Conf. Cosmo. Marseille 2004 GEANT4 Simulation (LPSC): Intrinsic rejection of neutrons and rays  Parallel ray discrimination necessary Ultraviolet scintillation ? Ionisation measurement ?

33. Alternative thermometry Microfabricated VWRs Si/Al (≤10 m) (Triquenaux et al., Physica B 2000) Thermometry by NMR H S Quantum coherent state of precession of magnetization Incident particle 100  K NMR signal 3 He Homogeneous Precession Domain - NMR 4 He, 30 mbar

34. Conclusions Experimental characterization of a prototype of a bolometric detector based on superfluid 3 He - Vibrating Wire thermometry - Bolometry Detection spectra of neutrons, low energy electrons and muons - neutralino detection threshold reached - good understanding of the detector Estimation of the scintillation yield of the irradiated superfluid  discrimination of electron recoils