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C. Winkelmann J. Elbs E. Collin Yu. Bunkov H. Godfrin E. Moulin J. Macias-Perez D. Santos

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) MA trix of C ells of superfluid He lium- 3.

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C. Winkelmann J. Elbs E. Collin Yu. Bunkov H. Godfrin E. Moulin J. Macias-Perez D. Santos

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  1. MACHe3: Prototype of a bolometric detector based on superfluid 3He 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. Missing Mass and non-baryonic Dark Matter • Flat Universe  ≈ c=5.1 GeV/m3 Wr + Wm + WL ≈ 1.0 • Energy density of matter in the Universe M ≈ 1.6 GeV/m3 Wm≈ 0.3 WL ≈ 0.7 Knop et al. (2003) Spergel et al. (2003) Allen et al. (2002)

  3. Vitesse de rotation (km/s) R0=8.5 kpcHonma et Sofue (1996) • Open questions in cosmology: • Presence of large scale structures imposes • rbaryons ≈ 0.2 - 0.3 GeV/m3 •  Anomalies of galactic rotation curves Rotation velocity km/s Measured Visible Matter contribution Standard Cold Dark Matter Simulation VIRGO

  4. Non-baryonic Dark Matter: Weakly Interacting Massive Particles Supersymmetric extension of Standard Model provides acandidate: neutralino c stable (except annihilation)  relic density massive (~ 100 GeV/c2)  Missing Mass neutral in charge and color  Weak interaction cross section with ordinary matter Direct detection ~ Scalar interaction Edelweiss, CDMS,CRESST, Zeplin Ge, Si, CaWO4, Xe Axial interaction DAMA/Libra, Picasso, Simple, MACHe3 NaI, F , 3He

  5. Project of bolometric detection based on 3He 3He • Spin 1/2 nucleus  axial interaction with neutralino • High transparency to g-rays • Nuclear neutron capture reaction • Limited recoil energy range: Erecoil < 6 keV At ultra-low temperature (100 mK, superfluid) • Specific heat  exp(-D/kBT) • Absolute purity • Liquid but: expensive, technologically challenging, …

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

  7. Vibrating wire thermometry at ultra-low temperatures

  8. The Vibrating Wire Resonator I0 eiwt H V (mV) Induced voltage V 3 mm NbTi Monofilament (4.5mm) (Photo E. Collin)

  9. Ballistic quasiparticle gas Non-linear damping E 1 2 3 4 +pFv D -pFv vrms (mm/s) p 0 -pF pF Doppler shift of dispersion curves selective scattering of quasiparticles (Andreev scattering) (Fisher et al., PRL 1989) Excitation force (pN)

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

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

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

  13. Heat capacities W (Hz) 1 0.01 0.15 0.4 5 Cqp CABS (Halperin) Cadd (Greywall) C (j/K) T (mK)

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

  15. 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 (g-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

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

  17. Neutrons Elastic diffusion m3He≈ mn  fast thermalisation of neutrons nuclear neutron capture fast neutron thermalisation and nuclear capture :  good neutron background discrimination

  18. Neutrons • good agreement with description of detector • Heat deposition : ( Bäuerle et al., Nature 1995) • Energy deficit of 15 % Detection spectrum at Wbase=0.7 Hz Moderated AmBe source Coups - Scintillation ? - Topological defects ? Meyer, Sloan, JLTP 1998 3H- 1 mm p 10 mm 70 mm p=0 bar

  19. Low energy electrons Radioactive decay Source is in situ (cell B) Moulin et al., to appear g-rays Electrons produced in gold sheet Internal conversion electrons 21.7 27.9 Auger electrons Pile-up 57Co emission 13.6 14.4 0.6 5.5 122 136 7.3 E (keV) 100 1 10

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

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

  22. Cosmic muons • Cosmic muon flux: Surface150 / m2.s Underground (Gran Sasso) 2.310-4 / m2.s • Large cross section (100 barns)  linear energy deposition (ionisation) dE/dx=1.9r[g/cm3]MeV/cm Expected energy deposition in bolometers ~ 70 keV • Coincident detection across cells coincidence Wmes(Hz) time (s)

  23. • Detection of cosmic muons: good agreement experience/simulation if fUV(muons) ≈ 25 % Analysis and simulation LPSC (GEANT4)

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

  25. Outlook for Dark Matter search Detector project (Mayet et al., NIMA 2002) • 103 cells of 53 cm3 • 10 kg 3He target material • Underground laboratory 5 cm

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

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

  28. Conclusions • Experimental characterization of a prototype of a bolometric detector based on superfluid 3He - 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

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