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Towards One Tonne WIMP Direct Detectors: Have we got what it takes? (CryoArray)

Towards One Tonne WIMP Direct Detectors: Have we got what it takes? (CryoArray). Rick Gaitskell Department of Physics & Astronomy University College London source at http:// www.hep.ucl.ac.uk/~gaitskel rick@gaitskell.com. Ge. Edelweiss (98). H-M (94). NaI. UKDMC (96).

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Towards One Tonne WIMP Direct Detectors: Have we got what it takes? (CryoArray)

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  1. Towards One Tonne WIMP Direct Detectors:Have we got what it takes?(CryoArray) Rick Gaitskell Department of Physics & AstronomyUniversity College London source at http://www.hep.ucl.ac.uk/~gaitskelrick@gaitskell.com

  2. Ge Edelweiss (98) H-M (94) NaI UKDMC (96) H’berg-Moscow (98), IGEX (00) [m=20 GeV] Cryodet [m=100 GeV] Homestake (87) DAMA (00) DAMA (98) CDMS SUF (99) Liq Xe DAMA (96) Edelweiss (01) (T) Target CDMS SUF (00) NOW Signal CDMS SUF (T) GENINO (T) 100 kg Ge Diode CDMS Soudan (T) 7 kg Ge+Si Cryodet GENIUS (T)100 kg Ge Diode CryoArray (T)0.1-1 tonne Cryodet Direct Detection: History & Future 90% CL Limit on Cross section for 60 GeV WIMP (scalar coupling) Different Colours Indicate Different Technologies Gaitskell (astroph 0106200) Oroville (88) ~1 event kg-1 day-1 ~1 event kg-1 yr-1 LHC ~1 event 100 kg-1 yr-1 [m = ?? GeV - if significantly better limit obtained at different mass] Not meant to be a complete list - see http://dmtools.berkeley.edu 010621.5.rjg

  3. Background Rejection / WIMP Signal Identification • Nuclear Recoil (WIMPs & neutrons) vs g • Cryogenic • Phonon + Ionisation or Photons (CDMS / Edelweiss / CRESST) • NaI • Scintil. Photon Pulse Shape (DAMA ‘96 / Boulby DM ‘97-’02) • Liquid Xe • Scintil Photon Pulse Shape (ZEPLIN I Boulby DM ‘01-) • Photon + Ionisation (ZEPLIN II+III Boulby DM ‘02- ) • Droplets • Superheated Bubbles (Picasso/Simple ‘01-) • Exploit WIMP “Wind” for signature • Annual Modulation • NaI (DAMA 100 kg ‘97-00, 250 kg ‘02-) • Direction Axis of Recoil • Gas TPC (DRIFT Boulby DM ‘01-)

  4. outer Pb shield scintillator veto Icebox polyethylene outer moderator detectors inner Pb shield dilution refrigerator CDMS I: SUF Site • Stanford Underground Facility • 17 mwe of rock • hadronic component down by >1000 • muon flux down by ~5 • Low-Background Environment • 25 cm polyethylene reduces muon-induced neutron flux from rock and lead by factor >100 • 15 cm Pb reduces photon flux by factor >1000 • radiopure cold volume (10 kg) • additional internal (ancient) lead shielding • Active Scintillator Muon Veto • muon veto >99.9% efficient • reject ~22 “internal” neutrons/ day produced by muons within shield • SHALLOW SITE SUFFERS FROM “EXTERNAL NEUTRONS” 20-600 MeV from muons in rock 010306.1.rjg

  5. CDMS: Ge BLIP Ionization & Phonon Detectors • Tower • Wiring • heat sinking • holds cold FETs for amplifiers BLIP • Four 165 g Ge detectors, for total massof 0.66 kg during 1999 Run • Calorimetric measurement of total energy • ENERGY Resolution • s = Ionisation 220 eV, Phonons 250 eV Inner Ionization Electrode Outer Ionization Electrode Passive Ge shielding (NTD Phonon Sensors on underside)

  6. Nuclear recoils arise from WIMPs Neutrons Electron Recoils arise from photons electrons alphas (Typical Background) Ionization yield ionization/recoil energy strongly dependent on type of recoil Recoil energy Phonons give full recoil energy CDMS Nuclear Recoil Discrimination - Event by Event NOT A SIMULATION! 1334 gamma events, 616 neutron events Gammas (external source) 1/2 year’s background Neutrons (external source) >> 1/2 year’s signal !! Trigger Threshold 010402.3.rjg

  7. Gammas Surface Betas Nuclear Recoils 1999 Run Ge BLIP Data Set Combined all single-scatters NR candidates Entire 96 live days operation Ge BLIPs = 10.6 kg-days • Gamma and electron bands well separated from NR band • NR candidates are truly NR’s • See a total of 13 events > 10 keV  ~ 1.2 events/kg/day Expect 40 events for scalar WIMP s given by the DAMA Ann Mod Signal NR Band asymmetric (-3s,+1.28s)= 90% efficient 010306.3.rjg

  8. B3 B4 B5 B6 WIMP SUSY CDMS I + II Status • CDMS I • Current limit based on 10.6 kg-days exposure (PRL 84 (2000) 5699) • 3x 160 g Ge detectors, with inner fiducial volume 46% • At TAUP will announce updated analysis based on larger fiducial vol • Volume 46% -> 65% • (See TAUP talk for new limit, and discussion of extra analysis) • CDMS II • Infrastructure/buildings installed at Soudan mine • New Tower, total 1 kg detectors being commissioned at Stanford Underground Facility • 6 dets: 2 50 g Ge + 100 g Si ZIPs • Tower will be installed in Soudan - January 2002 • Test systems Jan-Mar’02 • Low background operation Apr-Oct’02, target 44 kg-days Ge exposure which will push sensitivity to 0.07 events/kg/day in Ge (Er>10 keV) • Subsequent Towers installed 2003-2004 • Tower 1+2 - Operate Jan’03 -> (followed by more towers) • Tower 1 to 7 (Full complement 7 kg) Operate Jun’04 -> Z1 Ge Z2 Si Z3 Ge Z4 Si Z5 Ge Z6 Si

  9. Current Experimental & Theoretical Regions http://dmtools.berkeley.edu UKDMC H-M / IGEX DAMA(96) Edelweiss CDMS I DAMA Ann Mod Gondolo… (g-2) Ellis et al. Mandic et al Bednyakov et al. From limitplot27749 010612.2.rjg Updated

  10. Stanford Underground Site CDMS II: Site Depths & Muon Flux SUF->Soudan Muon Flux Falls by ~104.5 MC predict residual punch-through neutron signal 10-4 events/keV/kg/day 500 Hz muons in 4 m2 shield 1 per minute in 4 m2 shield Muon Flux (m-2s-1) Depth (mwe)

  11. CDMS II Detector Deployment @ Soudan • Already demonstrated discrimination to < 10 event / kg / year • >99.9% rejection of photons >10 keV (~0.5 events/keV/kg/day) • >99% rejection of surface-electrons >15 keV (~0.05 events/keV/kg/day) • Identical Icebox: 7 Towers each with three Ge & three Si ZIP detectors • Total mass of Ge = 7 X 3 X 0.25 kg > 5 kg • Total mass of Si = 7 X 3 X 0.10 kg > 2 kg

  12. 4 K 0.6 K 0.06 K 0.02 K Si ZIP Ionization & Phonon Detectors • Advanced athermal phonon detection technology • Superconducting thin films of W/Al ZIP: At end of fabrication steps involving µm photolithography at Stanford Nanofabrication Facility

  13. CDMS Ge & Si Fast Phonon & New Electrode Detectors Al/W Grid 8 Traps 37 - 5 mm 888 X 1 µm tungsten TES in parallel Squares Aluminum Collector Fins 60% Area Coverage

  14. ZIP Detector: Detail of film patterns • VIDEO NOT INCLUDED

  15. A D B C Delay plot xyZIP: Position Sensitivity y A D Px = (C + D - A - B)/(A+B+C+D) collimator X B C

  16. ZIP Detector: Operational Advantages • VIDEO NOT INCLUDED

  17. Detection Mechanisms Thermal Channel is dumping ground ultimately for all energy

  18. 104 – 105 increase over present limits 102 – 103 increase over expts under construction CryoArray: A 3rd Generation Experiment • Based on extrapolation of CDMS technology/strategy • Basic parameters/goals • 1000kg x 2 (live) years • >100 WIMPs at 10-46cm2 • <100 background events (prior to subtraction, eg, multiple scattering) • Reduce backgrounds • Internal (, ) and external (n) • Increase mass and manufacturability of detectors/cryo package • Maintain Performance • Possible sites • Soudan (CDMS II) among shallower site • National Underground Facility • Depth • Shared resources (vetos, assembly, materials screening, fabrication???)

  19. “CryoArray”: One Tonne Dark Matter Detector • New philosophy in deployment of cryogenic detectors • Use athermal phonon technology + ionisation to allow significant simplification of detector production and assembly • 100-1000 kg in 0.1-1 kg units • Challenge: Mass production/deployment • Detectors produced commercially by Si chip fab facility • Simple bilayer metal circuits (superconductors W & Al) • Appropriate volumes of SQUID electronics now available • Warm - Fermilab surface mount format • Cold - SQUID arrays available in quantity/consistency • Challenge: Modest improvements in existing performance…. • Event by event discrimination: Noise (<1 keV) well matched to WIMP recoil • CDMS I dets. showed 96 live days ‘free’ of systematics -> target 1 year free • Background reduction benefits from virtual elimination of passive material in detector space (self veto)

  20. CDMS I • Design Considerationsfor operation with (BLIP) thermal detectors • Low Thermal Load • Low Microphonics • (High impedance circuits) • Low IR leakage into 10 mK space (detector can’t take heat load)

  21. CryoArray • Design Considerations for (ZIP) non-thermal detectors • Non-thermal phonons • Most mounting hardware eliminated - low impedance so microphonics is not an issue • FET -> 4K (GaAs) or SQUID Q amp • Spatial Ch Multiplexing reduces electronics channels

  22. Nuclear recoils arise from WIMPs Neutrons Electron Recoils arise from photons electrons alphas (Typical Background) Ionization yield ionization/recoil energy strongly dependent on type of recoil Recoil energy Phonons give full recoil energy Nuclear Recoil Discrimination - Event by Event NOT A SIMULATION! 1334 gamma events, 616 neutron events Gammas (external source) Neutrons (external source) Phonon Trigger Threshold

  23. CryoArray (Sensitivity <1 per 100 kg-yr, s~10-46 cm-2) • Scale up to 1 tonne detector with target (90%CL) <1 evt per 100 kg-yr • Reduce g/b backgrounds by factor 20 vs CDMSII • g 0.25 -> 0.015 cts/keVee-1kg-1day-1 • (This compares to 0.050 keVee-1kg-1day-1 @15 keV for HMDS) • b 0.02 -> 0.001 cts/keVee-1kg-1day-1 • (Challenge to survey surfaces to this sensitivity) • Improve g/b rejection by factor 1-few! • g 99.5% -> 99.95% (1 in 2000) • CDMS I 1999 in-situ calibrations already showed 99.96% (17k event calibs) • b 95% -> 99.5% (1 in 200) • Ge BLIP with aSi contact, (E>25 keVr ) >95% (E>40 keVr) >99.5%, • Si ZIP using phonon rise times (E=10-20 keVr ) >98%, (E>20 keVr) >99.5% • Without Discrimination: • needs ~104 reduction in background from present (HM) levels 010708.2.rjg Revise rej

  24. x20-1 x3-1 x10-1 Background Projections - CryoArray (1 tonne) ALREADY HAVE 99.96% IN CDMS I dru = 1 event keV-1 kg -1 day -1 Energy Range 15-45 keV 010708.2.rjg H-M entry

  25. Nuclear recoils arise from WIMPs Neutrons Electron Recoils arise from photons electrons alphas (Typical Background) Ionization yield ionization/recoil energy strongly dependent on type of recoil Recoil energy Phonons give full recoil energy Nuclear Recoil Discrimination - Event by Event 1334 gamma events, 616 neutron events Gammas (external source) Neutrons (external source) Phonon Trigger Threshold

  26. x20-1 Background Projections - CryoArray (1 tonne) dru = 1 event keV-1 kg -1 day -1 Energy Range 10-40 keV

  27. Soudan Neutron Background in CryoArray • Expect dominant component from muon interactions in rock • Veto in cavity difficult – neutrons from 2 – 3 meters in • Polyethylene shield transparent above 50 MeV • Need factor x20 improvement vs CDMS II • Increase depth to => 4000 mwe • Instrument the rock with 2.5 m streamer tubes. • Preliminary simulations indicate >75% of emergent HE neutrons from hadron cascades are >50-cm transverse size. • Augment with ‘umbrella’ veto • Increase shield density inside veto

  28. Problem: Performance -> Production Mass • Recent challenge has been to demonstrate novel techniques • Low backgrounds &/or Discrimination • Now it is time to solve some of problems of scale up … • Detector production issues (+larger sizes of collaboration) • … and background reduction • What screening techniques are required? (Low energies / Monte Carlo??)Eliminating gamma/beta contamination in energy range 5-100 keVee is new field. • Discrimination: Improvements can be shared between improved backgrounds and improved rejection performance • Good experience of running technology underground • True comparison of technologies can only come once data from extended operation underground is available - highlights systematics

  29. x2 x2 x1 x1 2nd Kind of Limit on Threshold of Discrimination Background (e.g. Gamma or Surface Betas) Lateral spread of lines simulates noise For 1st case - (see CDMS talks on surface electron confusion with nuclear recoils) 1st Kind 2nd Kind In 2nd case - will single event in x1 only be background free? Signal (Nuclear Recoil) Effective threshold raised due to event-by-event discrimination confused by noise In this region x2 channel for signal events are buried in noise: Example where 2nd limit on discrimination may be relevant:CRESST x1(phonon) x2(photon) CaWO4 Gamma: x1=50 keVee x2~350 eVdet [based on current #’s - see CRESST II talk] Neutron: x1=50 keVee&r x2~50 eVdet (close to noise threshold) Assumes 0.7% energy of electron recoil signal detected in photons for gamma eventand QF (established for O nuclei recoils relative to gammas) is 14%

  30. (q=0) Rate~A2 (s=5 10-42 cm2, m=300 GeV) 131Xe,127I 73Ge 40Ar,~32S Rate kg-1day-1 Ge=15 keVee (30%QF) Solid line is integrated rate above threshold (dotted is differential rate) Xe=10 keVee (20%QF) I=4.5 keVee (9%QF) Recoil Energy Threshold [keVr] Influence of Coherence & Form Factor

  31. Collaboration & Funding Issues • Strong interest among CDMS Collaborators • Factor of 2 – 3 expansion in scale • Not costed or scheduled in any detail (requires technology/production studies) • Likely to require international collaboration • Include cryo detector groups in Europe • Funding – CDMS model • NSF • DoE Labs (LBNL, FNAL) • DoE University Programs • ++ International Component • Timescale • CDMS II detector production and test facilities begin to ramp down end of 2004. • Reasonable to ramp up development and use these facilities + new facilities while taking data with CDMS II Experiment up and running. Therefore would seek detector development funding ~2002-4, project funding ~2005. • Other factors include CDMS II technical and scientific developments, as well as results from the rest of the community.

  32. Ge Edelweiss (98) H-M (94) NaI UKDMC (96) H’berg-Moscow (98), IGEX (00) [m=20 GeV] Cryodet [m=100 GeV] Homestake (87) DAMA (00) DAMA (98) CDMS SUF (99) Liq Xe DAMA (96) Edelweiss (01) (T) Target CDMS SUF (00) NOW Signal CDMS SUF (T) GENINO (T) 100 kg Ge Diode CDMS Soudan (T) 7 kg Ge+Si Cryodet GENIUS (T)100 kg Ge Diode CryoArray (T)0.1-1 tonne Cryodet Direct Detection: History & Future 90% CL Limit on Cross section for 60 GeV WIMP (scalar coupling) Different Colours Indicate Different Technologies Gaitskell (astroph 0106200) Oroville (88) ~1 event kg-1 day-1 ~1 event kg-1 yr-1 LHC ~1 event 100 kg-1 yr-1 [m = ?? GeV - if significantly better limit obtained at different mass] Not meant to be a complete list - see http://dmtools.berkeley.edu 010621.5.rjg

  33. http://dmtools.berkeley.edu http://dmtools.in2p3.fr Current SUSY Theory CDMS (Feb 2000) ~1 event/kg/d ~1 event/kg/yr ~ 1 event/100 kg/yr CryoArray 1 tonne event by event discrim.

  34. Projected Experimental & Theoretical Regions http://dmtools.berkeley.edu IGEX UKDMC NaIAD GENIUS TF 11 keV Gondolo… (g-2) GENIUS TF 2 keV Ellis et al. GENINO Mandic et al CDMS II Soudan / Edelweiss II GENIUS CryoArray From limitplot27749 010612.2.rjg Updated

  35. One Tonne: Conclusion • Discriminating Detectors • Allows sharing of improvement budget (target 104 over current sensitivity) • Good discrimination uses Ge/Si (expensive) target very efficiently • Will allow us to study WIMP physics (~100 events) at s~10-46 cm2, with background ~100 events characterised 5s (Even better for higher cross-sections) • CryoArray (based on CDMS technology) see Gaitskell/astro-ph 0106200 • Discrimination: g good enough, b within factor few • Based on extensive underground running of Ge/Si detectors (1996->) so stats reflect real world scenario • Backgrounds: x20 reductions vs CDMS II, x3 vs best current Heidelberg-Moscow • Modest b/g reduction should be possible through materials selection/simplification of structures (little mounting material) • Scaling up to 1000’s detectors • CDMSII 42 dets (250 g Ge) / CUORE -> 1000 dets • Fabrication of dets in commercial environment is the challenge • 10 year development : means opportunity to capitalise on technology

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