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AN EXPERIMENTAL OVERVIEW OF Direct Dark Matter Searches

AN EXPERIMENTAL OVERVIEW OF Direct Dark Matter Searches. Henrique Araújo Imperial College London IOP2010 – JOINT HEPP/APP GROUP MEETING 29-31 March 2010, University College London. What are we looking for?. Scalar (SI) and axial-vector (SD) c -N interactions (neutral current exchange):.

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AN EXPERIMENTAL OVERVIEW OF Direct Dark Matter Searches

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  1. AN EXPERIMENTAL OVERVIEW OFDirect Dark Matter Searches Henrique Araújo Imperial College London IOP2010 – JOINT HEPP/APP GROUP MEETING 29-31 March 2010, University College London

  2. What are we looking for? • Scalar (SI) and axial-vector (SD) c-N interactions • (neutral current exchange): WIMPs attract most experimental effort, but axion searches are a growth industry I assume here that the Lightest SUSY Particle is the neutralino, c, which is a great WIMP WIMPs should scatter off ordinary nuclei producing measurable nuclear recoils But, essentially, WIMP searches are not really (PP-)model dependent… H. Araújo

  3. Low energy nuclear recoils • Elastic scatter off nucleus: • Decreasing, featureless spectrum of low-energy recoils (<~50 keV) • Rate depends on target mass & spin, WIMP mass & spin, DM halo, … • Neutrons are irreducible background • Inelastic scatter off nucleus: • Short-lived, low-lying excited states (easier signature?) • 129Xe(3/2+→1/2+) + g(40 keV), 73Ge(5/2+→9/2+) + g(13 keV) • Neutrons are irreducible background • Inelastic dark matter (iDM): • “particles will scatter at DAMA but not at CDMS” (Smith & Weiner 2001) • Recoil spectrum with threshold (mass splitting, d) • Neutrons are irreducible background H. Araújo

  4. Elastic scattering rates Canonical model: not great, but we’re all in this together: • Isothermal sphere (no lumps), r∝ r−2 • Local density r0~0.3 GeV/c2/cm3 (~1/pint at 100 GeV) • Maxwellian (gaussian) velocity distribution • Characteristic velocity v0=220 km/s, • Local escape velocity vesc=600 km/s • Earth velocity vE=232 km/s H. Araújo

  5. Elastic scattering rates • Coupling to protons and neutrons more useful than coupling to nucleus • To compare different target materials, indirect searches, LHC results • Spin-independent (scalar) interaction • note A2 in enhancement factor • cMSSM-favoured XS within reach of current detectors • Spin-dependent (axial-vector) interaction • note J (nuclear spin) instead of A2 enhancement • cMSSM-favoured XS out of reach for the time being… H. Araújo

  6. SI scattering rates for 1 kg targets H. Araújo

  7. The experimental challenge • Low-energy particle detection is easy ;) E.g. Microcalorimetry with Superconducting TES Detection of keV particles/photons with eV FWHM! • Rare event searches are also easy ;) E.g. Super-Kamiokande contains 50 kT water Cut to ~20 kT fiducial mass (self-shielding) • But doing both is hard! Small is better for collecting signal Large is better for background • Ah: and there is no trigger… H. Araújo

  8. Consider 1 kg target Sensitive to Edep>1 keV Expected WIMP rates 0.1−0.000001 evt/day However… Cosmic rays, a, b, g-rays >1,000,000 evt/day Neutrons are THE background! Several evt/day m b g n a Building a WIMP detector WIMP 1 kg H. Araújo

  9. Move underground Use radio-pure materials Shield external g-rays Shield external neutrons Actively veto neutrons Discriminate e-recoils (g, b) from n-recoils (WIMPs, n) Building a WIMP detector WIMP H. Araújo

  10. Nuclear recoils - backgrounds • Nuclear recoils – same signature • Neutrons from (a,n) and SFissionfrom U/Th trace contamination • Laboratory walls, shields, vessels, components, target material • Neutrons from atmospheric muon spallation • Difficult to shield completely even underground • Recoils from alpha emitters (e.g. Rn-222 and progeny) • Contaminating active target bulk/surfaces, air, etc • Eventually, even coherent neutrino scattering • Electron recoils – discrimination power is limited • Gamma-ray background external to target • K-40, Cs-137, U/Th from walls, shields, vessels, components • Contamination of target bulk and surfaces • U/Th betas and gammas (Pb-214, Bi-214, Pb-210,…) • Cosmogenic (Ge-68, Ge-71,…), anthropogenic (Kr-85, Cs-137,…) H. Araújo

  11. laboratory system incoming neutron En q nuclear recoil ER En ’ Nuclear recoils - signal acceptance Ge (CDMS-II) • 100 GeV WIMP on Xe (A=131): • 220 km/s WIMP → ER,max = 40 keV • 1 MeV neutron → ER,max = 30 keV • Neutron elastic scattering populates WIMP acceptance region • Calibration of detection efficiency with Am-Be (a,n), Cf-252 (SF), D-D, D-T • But there are complications: • Multi-element: in CaWO4 (CRESST), WIMPs couple mainly to heaviest material (W), but neutrons scatter mainly off lightest (O). Signal acceptance must be calibrated indirectly • Quenching factor: in noble liquids (ZEPLIN,XENON,WARP,ARDM,…) conversion from “electron-equivalent” to nuclear recoil energy is not straightforward (or favourable…) • Droplets: in C4F10 superheated droplets (SIMPLE,PICASSO) phase transition is independent of energy. Calibration of signal acceptance threshold only H. Araújo

  12. ionisation Q L scintillation H phonons Discrimination: single channels Ionisation Detectors Targets: Ge, Si, CS2, CdTe CoGeNT, DRIFT, GENIUS, HDMS, IGEX, NEWAGE Scintillators Targets: NaI, Xe, Ar ANAIS, CLEAN, DAMA, DEAP, KIMS, LIBRA, NAIAD, XMASS, ZEPLIN-I Bolometers Targets: Ge, Si, Al2O3, TeO2 CRESST-I, CUORE, CUORICINO Bubbles & Droplets CF3Br, CF3I, C3F8, C4F10 COUPP, PICASSO, SIMPLE H. Araújo

  13. ionisation Q L scintillation H phonons Discrimination: hybrid detectors Heat & Ionisation Bolometers Targets: Ge,Si CDMS, EDELWEISS cryogenic (<50 mK) Light & Ionisation Detectors Targets: Xe, Ar ArDM, LUX, WARP, XENON, ZEPLIN cold (LN2) Light & Heat Bolometers Targets: CaWO4, BGO, Al2O3 CRESST, ROSEBUD cryogenic (<50 mK) All 3 hybrid technologies > 99.9% discrimination @ >10 keV NR energy H. Araújo

  14. Phonons (microcalorimetry) Cryogenic: T0~50 mK Thermal phonon signal is lost with increasing mass: must collect phonons before they thermalise in absorber • Superconducting Transition-Edge Sensor (as in CDMS) • Collect high-frequency (athermal) phonons from particle interaction • Into superconducting Al contacts (threshold 2DAl~ meV) • Quasiparticles from broken Cooper pairs diffuse into a W TES • SQUID readout offers extremely high sensitivity • Channel threshold: 1 keV for Ge & Si nuclear recoils J. Cooley, CDMS Collaboration H. Araújo

  15. Scintillation (photomultipliers) DAMA/LIBRA Collaboration Room temperature, cold or cryogenic NaI, CsI, CaWO4, LXe, LAr: many materials scintillate… Photomultipliers: ancient vacuum tube technology, but no-one has come up with a better alternative yet (and we’re trying…) • Scintillation detectors (as in DAMA) • Best photomultipliers now approaching 50% quantum efficiency • Best NaI(Tl) crystals yield ~90 photons/keV for gamma rays • Typically require coincidence of two photomultipliers (2 phe) • Threshold: 0.3-3 keV for I nuclear recoils • (depending on “channelling” effect) H. Araújo

  16. S2 (electroluminescence) Ionisation(Electroluminescence, TES, HEMT, JFET) Cold: T0~200 K Difficult to measure one electron, but not so hard to measure electroluminescence photons from one electron • Two-phase xenon detectors (as in ZEPLIN) • Strong electric field across liquid-gas xenon target • Collect ionisation from particle track in liquid Xe • Drift up to surface, then emit into vapour phase • Electroluminescence photons detected with photomultipliers • Threshold: 0.2 keV for Xe nuclear recoils 1e Edwards et al., Astroparticle Phys. 30 (2008) 54 H. Araújo

  17. A few examples(not comprehensive and somewhat UK-centric) H. Araújo

  18. CRESST: Scintillation & Phonons Target: 0.6 kg CaWO4 3 events observed in 10-40 keVnr acceptance region 48 kg·days exposure (2007) Angloher et al, Astropart. Phys. 31 (2009) 270 H. Araújo

  19. ZEPLIN-III: Scintillation & Ionisation Target: 12 kg LXe 7 events observed in 10-30 keVnr acceptance region 850 kg·days raw exposure (2008) (likely e-recoil background) Lebedenko et al, PRD 80 (2009) 052010 H. Araújo

  20. CDMS-II: Ionisation & Phonons Target: 4.4 kg Ge, 1.1 kg Si 2 events observed in 10-100 keVnr acceptance region 612 kg·days exposure (2007-08) Background estimate 0.8±0.2! Ahmed et al, arXiv:0912.3592 H. Araújo J. Cooley, CDMS Collaboration

  21. DAMA/LIBRA: Scintillation Target: 250 kg NaI(Tl) 8.9s CL modulation over 13 annual cycles Barnabei et al, arXiv:1002.1028 (But what is modulated? and is it getting smaller?) H. Araújo

  22. DRIFT – NI Gas TPC Target: 167 g/m3 CS2 (now CS2+CF4) Unlikely that backgrounds mimic signal which appears as forward/backward asymmetry in galactic coordinates H. Araújo

  23. PICASSO: Superheated C4F10 Target: 65+69 g C4F10 H. Araújo

  24. CoGeNT - Ionisationp-type point contact (PPC) HPGe Target: 330 g Ge Excess at low energies – a glimmer? Aalseth et al, arXiv:1002:4703v2) No discrimination, too close to threshold… H. Araújo

  25. World status & prospects (SI) H. Araújo

  26. World status & prospects (SD) H. Araújo

  27. World status & prospects (iDM) Schmidt-Hoberg & Winkler, JCAP09(2009)010 Akimov et al., arXiv:1003.5626 (ZEPLIN-III) H. Araújo

  28. Next generation: a view TWO-PHASE ARGON • A=40, <ER>= 13 keV @50 GeV/c2, 35 keV @500 GeV/c2 • very scalable (cheap, large LAr systems demonstrated) • poor energy threshold, low atomic weight, Ar-39 background • WARP, ArDM, (DEAP/CLEAN) working on 0.1—1 tonne targets • 5-tonne system within 5 years is (optimistically) possible CRYOGENIC GERMANIUM • A=73, <ER>= 13 keV @50 GeV/c2, 57 keV @500 GeV/c2 • excellent energy resolution, excellent discrimination • difficult to scale (small detector modules, <50 mK cryostats) • CDMS, EDELWEISS, (CRESST) working on 10—20 kg targets • EURECA and SuperCDMS propose ~100 kg target in 5 years TWO-PHASE XENON • A=131, <ER>= 11 keV @50 GeV/c2, 85 keV @500 GeV/c2 • scalable, low threshold • control of xenon purity to <ppb is demanding • ZEPLIN-III, XENON100, LUX350, (XMASS), working on 10-100 kg • XENON1T and LUX-ZEPLIN propose 1 tonne two-phase xenon targets Proposals (>1 tonne) CDEX, CLEAN, COUPP+, DAMA+, DARKSIDE, DARWIN, DEAP3600, DRIFT, EURECA, GEODM, KIMS+, LUX-ZEPLIN, MAX, SuperCDMS, XMASS, … H. Araújo

  29. Next generation: a view Araujo, Strigari & Trotta Araujo, Strigari & Trotta H. Araújo

  30. Ready to scale up! Pack ? UK pioneered several search technologies NaIAD, ZEPLIN-I, DRIFT-I, CRESST-I, ZEPLIN-II, DRIFT-II, CRESST-II, ZEPLIN-III, ArDM, EDELWEISS, (EURECA, LZ) And pushed forward “underground science” Dating back to Holborn Station Laboratory… Creating the Boulby Underground Laboratory (see Sean Paling’s talk tomorrow) But we’re running out of road… H. Araújo

  31. Click to add funding Thank you

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