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

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

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)

Open questions in cosmology:  Presence of large scale structures imposes  baryons ≈ 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

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

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, …

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

Vibrating wire thermometry at ultra-low temperatures

3 He superfluide fermion: (2p + n) + 2e - A T c ~ 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 

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)

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

 (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

Amortissement Fil Vibrant  n qp  pFpF -p F E p 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

Ballistic quasiparticle gas  +p F v -p F v pFpF -p F E p 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)

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)

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)

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) +

C (j/K) T (mK) C qp C ABS (Halperin) W (Hz) Heat capacities C add (Greywall)

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)

 1/√T Bolometric calibration by pulsed heating

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

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

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

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

Low energy electrons Radioactive decay Source is in situ (cell B) E (keV) 57 Co emission Pile-up Electrons produced in gold sheet Moulin et al., to appear  rays Internal conversion electrons Auger electrons

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)

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

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)

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

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

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

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 ?

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

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