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The C ryogenic

The C ryogenic. D ark. M atter. S earch. Michael B. Crisler Fermi National Accelerator Laboratory 03 June 2003. CDMS Collaboration. Case Western Reserve University

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The C ryogenic

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  1. The Cryogenic Dark Matter Search Michael B. Crisler Fermi National Accelerator Laboratory 03 June 2003

  2. CDMS Collaboration • Case Western Reserve University • D.S. Akerib, A. Bolozdynya, D. Driscoll,S. Kamat, T.A. Perera, R.W. Schnee, • G.Wang • Fermi National Accelerator Laboratory • M.B. Crisler, R. Dixon, D. Holmgren, • M. Haldeman • Lawrence Berkeley National Laboratory • J. Emes, R.J. McDonald, R.R. Ross, A. Smith • National Institute of Standards • and Technology • J. Martinis • Princeton University • T. Shutt • Brown University • R.J. Gaitskell, M.J. Attisha, • J-P.F. Thompson • University of Minnesota • P. Cushman, L. Duong, A. Reisetter • Santa Clara University • B.A. Young • Stanford University • L. Baudis, P.L. Brink, B. Cabrera, J.P. Castle, C.Chang, R. M. Clarke, A.K. Davies, M.Hennessey, M. Kurylowicz, S.W. Nam, W.Ogburn, A.Perales, T. Saab, A. Tomada • University of California, Berkeley • M.S. Armel, J. Alvaro-Dean, S. Golwala, • J. Helmig, A. Lu, V. Mandic, P. Meunier, • N. Mirabolfathi, M.C. Perillo Isaac, W. Rau, • R.R. Ross, B. Sadoulet, D. Seitz, G. Smith, • A.L. Spadafora • University of California, Santa Barbara • D.A. Bauer, R. Bunker, D.O. Caldwell, • R. Ferrl, R. Mahapatra, C. Maloney, • H. Nelson, R. Nelson, J. Sander, C. Savage, S. Yellin • University of Colorado at Denver • M. E. Huber

  3. Galactic Big Picture WeaklyInteracting Massive Particles nuclear recoil ~ 10’s of keV

  4. Latest Results from WMAP Bennett et al. Wb = 0.044 WM = 0.27 WL= 0.73 Wtotal = 1.02

  5. WIMP Velocity Plot Halo model provides reliable estimate of particle flux a2+r02 r(r) = r0 a2+r2 r0 = 0.3GeV/cm3 a = 6.4kpc v0 = 220 km/sec r0 = 8 kpc Typical collision velocity ~ 320 km/sec 7% annual modulation 1 exp(v2/v02)d3v f(v) d3v = p3/2 v03 particle flux Fx = r0v/mx Erecoil ~ ½ mN v2WIMP ~ 10’s of keV

  6. Interaction Rate mx is unknown …but we can guess lightest superpartner? mx ~100 GeV/c2 particle flux Fx = r0v/mx depends only on the halo model (and on mx) sx is unknown …but we can guess from big-bang: Density Wx ~ 1 / interaction rate Wx ~ .3 => sv ~ 10-26 cm3/s sx ~ sweak Standard assumption: scalar interaction => sNUCLEUS = A2sNUCLEON

  7. …Quantification of Our Ignorance DAMA experiment possible signal unknown mx Current CDMS SUF Limit Projected Soudan Site 1 Month unknown sx Projected CDMS Soudan Limit Your favorite SUSY models

  8. Technical Challenges: Very Small Signals characteristic nuclear recoil energy ~ 10 keV Very Low Count Rates expect << 1 event /kg/day Plenty of Background gamma, beta, neutrons from cosmic rays, contamination, radon…

  9. CDMS Experimental Strategy powerful new solid state detectors Simultaneous Measurement of Erecoil and Qionization Separate Gamma and Beta interactions (most of the background) from true nuclear recoils (neutrons or WIMPs) Optimize our shielding design to minimize neutron backgrounds Underground site Stanford Underground Facility (35’, 17 mwe) Soudan Mine Underground Laboratory (2500’) Other Analysis Handles for neutron rejection: Multiple scattering analysis (WIMPS don’t, neutrons do…) Two target materials Si for neutrons, Ge for WIMPs Independent Monte Carlo Analysis of neutron flux

  10. CDMS Detectors pure Si or pure Ge solid state detectors 1 cm very cold ~ 0.01 oK Direct calorimetric measurement of Erecoil ionization efficiency Q/Erecoil --> provides particle ID electrode segmentation for position sensitivity conventional measurement of ionization Q

  11. Athermal Phonon Detection Scattered particle tungsten sensor prompt phonon detection with segmented electrodes Superconducting Al phonons Ge crystal localize the interaction within the crystal Speed of sound in Si (Ge) = 1 (0.5) cm/ms Transition Edge Sensor Power = V2 / R Electro-Thermal Feedback heat R Quasi-particle excitations (broken cooper pairs) bias here… ~80 mK phonon Quasiparticle Trap Assisted temperature

  12. The CDMS ZIP Detectors superconducting normal resistance ETF-TES region 1 mm

  13. Phonon and Charge Pulses in Si and Ge noise < 1 keV

  14. CDMS ZIP Detector: Source Calibration gammas ionization efficiency nuclear recoils ERECOIL ERECOIL

  15. Phonon Response … Position Sensitivity Am241 : g 14, 18, 20, 26, 60 kev Cd109 + Al foil : g 22 kev Delay Plot A D Cd109 : g 22 kev i.c. electr 63, 84 KeV B C T. Saab, Stanford U. from GSFC Talk 2002

  16. Phonon Rise-time … Depth Sensitivity b Incomplete charge collection at the surface electrons gammas g neutrons n (WIMP) surface bulk

  17. 1999 Data Set …3 pre-ZIP Ge Detectors Inner-Electrode Shared-Electrode Inner-electrode B3 B4 B5 Shared-electrode B6 23 events consistent with WIMPs 4 double scatters… ionization efficiency 4 events on Si… 1998 Data Set …1 Si ZIP ionization efficiency , except… All 1998/1999 data consistent with neutrons only

  18. CDMS I->II Go deep underground Athermal phonon technology Even better rejection of background Increase the mass -> 7kg 7 towers of 6 detectors Approved in January 2000

  19. 2001/2002 Data Set …full tower 4 Ge, 2 Si ZIPs non-neighbor double scatters triple scatters ! 2 Si events increased polyethelene shielding reduced neutron flux by 2.3 28.3 kg-days for WIMPs 20 Ge nuclear-recoil candidates > 5 keV Again consistent with neutrons only

  20. CDMS Sensitivity (Stanford Underground Facility) DAMA CDMS 1998/99 no subtraction CDMS new… Edelweiss !

  21. Stanford U. Campus 2500 feet 30 feet

  22. Downtown Ely, Minnesota (shown here during rush hour…) T. Saab, Stanford U.

  23. Soudan Shielding Assembly

  24. Pb Lid in Place

  25. Cryo Plant in Place (CDMS WEBCAM)

  26. Source Calibration (CDMS WEBCAM)

  27. Veto Shield in Place (CDMS WEBCAM)

  28. CDMS Status / Summary Two Full Towers of Detectors in Place at Soudan including the one used for data taking at Stanford system has been cold and fully operational. One more cryo bug… Beam Continues to Run Smoothly… Much excitement about repeating this measurement with the exact same apparatus… Expect Data this Summer …only 2465’ further underground

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