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The Cryogenic Dark Matter Search: CDMS

The Cryogenic Dark Matter Search: CDMS. Nader Mirabolfathi UC Berkeley STD6, Carmel CA, September 2006. Dark matter, WIMPs; Direct detection. Very low temperature detectors: CDMS detection method CDMS results from Soudan underground laboratory CDMS perspective and future.

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The Cryogenic Dark Matter Search: CDMS

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  1. The Cryogenic Dark Matter Search: CDMS Nader Mirabolfathi UC Berkeley STD6, Carmel CA, September 2006 • Dark matter, WIMPs; Direct detection. • Very low temperature detectors: CDMS detection method • CDMS results from Soudan underground laboratory • CDMS perspective and future

  2. Dark Matter : There is something invisible Spiral Galaxy Observed Expected

  3. CMB Large scale structure Galaxy clusters Gravitational lensing

  4. The Universe pie • Many candidates proposed among which WIMPs, a generic name for the massive particles (~10 to 1000 GeV) interacting at the weak scale (~10-43 cm2) seems very plausible. • If  is the Lightest Super-symmetry partner (LSP) then it could be WIMPs. • A direct detection of WIMPs will then be at the cross road of cosmology and particle physics.

  5. c c c c ~ q q q q q Rate < 1 event/kg/day isothermal Maxwell-Boltzmann distribution Few 10s of keV recoil energy Escape velocity=680 Km/s V0 = 230 Km/s Rate ~ N nc <sc> = 0.3 GeV/cm3 The most important challenge to detect WIMPs is the background: An event-by-event background rejection is inevitable. Photo from Z.Frei and E.Gunn

  6. CDMS background discrimination principle + + + + + + + - - - - - - - Ionization Thermal T=E/CV I=Y·E/gap Efield Ge or Si YNR<YER In Germanium Ionization yield for a NR (WIMPs) is 3 times smaller than an ER event (Radioactive).

  7. A back of the envelope calculation 1 kg Ge T=0.02 K 2 V R () 1.0 T (K) 0.02 Germanium at 300 K CV=3200 J/kg·K and D=374 K CV at 0.02 K = 5e-10 J/kg·K =3e6 keV/kg·K Therefore for a 1kg Ge absorber cooled down to 0.02 K, T caused by a 10 keV deposit will be: ~3.3e-6 K Superconductor Transition Edge Sensor A thermometer attached to the absorber with  ~100: Signal I~ 40 nA Noise~1pA/(Hz)^1/2 Typical for SQUID Amplifiers Very good resolution

  8. 20 micron 10 micron <5 micron Charge deficit Signal Not the end of the story: Dead layer? Electron recoil Electron recoil but Near the physical surfaces Nuclear recoil E=3Volts/cm, T<0.04 K

  9. d4> d3> d2> d1 d4 d1 d2 d3

  10. Athermal phonon: Phonons which are produced immediately after interaction • As thermal phonons (T measurement) we can estimate the total energy. • We look at the out of equilibrium phase of the thermal process. • We can reconstruct the history of an event including the position of an event: Identification of the near surface events

  11. Position reconstruction:example 109Cd (22 keV X, 60 & 85 keV e-) 241Am(60 keV& <24keV X) Sensing athermal phonons  Position dependence of the parameters

  12. Surface event identification 252Cf , neutron calibration Accept  calibration Reject Surface events More than 99.99 % rejection efficiency

  13. CDMS II ZIP Detectors • Detectors • 250 g Ge or 100 g Si crystal • 1 cm thick x 7.5 cm diameter Phonon Sensors • Photolithographic patterning • 4 quadrants • 37 cells per quadrant • 6x4 array of 250mm x 1mm W TES per cell • Each W sensor “fed” by 8 Al fins 60 mm wide 380 m Al fins • Ionization Sensors • 2 electrodes (+ ground) • Allow rejection of events near outer edge ZIP: Z-sensitive Ionization and Phonon Detector

  14. 1

  15. Tungsten, TC <80 mK Aluminum, TC=1.2K Ge absorber

  16. Phonon + Ionization – CDMS II ZIP Detectors • Detectors • 250 g Ge or 100 g Si crystal • 1 cm thick x 7.5 cm diameter Phonon Sensors • Photolithographic patterning • 4 quadrants • 37 cells per quadrant • 6x4 array of 250mm x 1mm W TES per cell • Each W sensor “fed” by 8 Al fins 60 mm wide 380 m Al fins • Ionization Sensors • 2 electrodes (+ ground) • Allow rejection of events near outer edge ZIP: Z-sensitive Ionization and Phonon Detector

  17. CDMSII Readout/Cold-hardware • Phonon signals are readout by SQUID based Amps (0.6 K) • Charge Amps first stage: Cold FET (130 K) • Both SQUID and FET based amps are assembled on a single card (SQUETs) • A CDMS “tower” consist of 6 ZIPs and corresponding SQUETs. currently running with 5 Towers:4.5 kg of Ge

  18. CDMS shields p+ p+ n n n n p+ p+ Surface CDMS MINOS 780m (2090mwe) SUF 12 m deep:50 /Sec.m2 Soudan 789 m deep: 0.004 /Sec.m2

  19. CDMS Two tower run result: Run119 T2 T1 1.5 1.0 0.5 0.0 Z2/Z3/Z5/Z9/Z11 Ionization Yield One candidate (10.5 keV) One near-miss noisy poor phonons 0 10 20 30 40 50 60 70 80 90 100 Recoil Energy (keV) 14C contam. “bad” region March 25, 2004 – August 8, 2004 96.8 (31.0) kg-days 0.4±0.2±0.2 Ge background expected -> 1 seen 0.4±0.9±0.5 Si background expected -> 0 seen

  20. CDMSII spin-independent limit CDMS II Soudan combined runs Si (2005) Phys. Rev. Lett. 96 (2006) 011302 CDMS II Stanford (2003) Edelweiss I 2005 (o) DAMA/NaI ZEPLIN I 2005 (x) CDMS II Soudan First run (1 tower) Ge (2004) CDMS II Soudan combined runs Ge (2006) MSSM example from Baltz & Gondolo (2003) CMSSM example from Ellis et al. (2005)

  21. Edelweiss ‘05 ZEPLIN I ‘05 CDMS Soudan ‘05 CDMS Soudan ‘07 25 kg 150 kg 1 ton CMSSM, Ellis et al. ‘05 MSSM, Baltz & Gondolo ‘03 CDMSII: More interesting results to come up Now running

  22. CDMS Future: SuperCDMS 2x better coverage 2.5x Volume/surface Modified ZIP TES Current ZIP TES • These detector improvements combined  10x better identification of near surface events. • Better control on contaminants by 2x • Better phonon signal position reconstruction  2x • Overall 40x lower background Amorphous Si 2x on back diffusion blockage + H2 to passivate the Si

  23. The CDMS Collaboration Brown University M.J. Attisha, R.J. Gaitskell, J-P. F. Thompson California Institute of Technology Z. Ahmed, S. Golwala, G. Wang Case Western Reserve University D.S. Akerib, C.N. Bailey, M.R. Dragowsky, D.R. Grant, R. Hennings-Yeomans, R.W.Schnee Fermi National Accelerator Laboratory D.A. Bauer, M.B. Crisler, D. Holmgren, E. Ramberg, J. Yoo National Institute for Standards and Technology K. Irwin Santa Clara University B.A. Young Stanford University P.L. Brink, B. Cabrera, J. Cooley, M. Kurylowicz, L. Novak, R. W. Ogburn, M. Pyle, A. Tomada University of California, Berkeley M. Daal, J. Alvaro-Dean, J. Filippini, P.Meunier, N. Mirabolfathi, B. Sadoulet, D.N.Seitz, B. Serfass, K. Sundqvist University of California, Santa Barbara R. Bunker, D.O. Caldwell, R. Mahapatra, H. Nelson, J. Sander, S.Yellin University of Colorado at Denver & Health Sciences Center M. E. Huber University of Florida, Gainesville L. Baudis, S. Leclercq, T. Saab University of Minnesota S. Corum, P. Cushman, L. Duong, X. Qiu, A. Reisetter

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