1. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 1 The Search for Dark Matter in the form of WIMPs: CDMS (Cryogenic Dark Matter Search) Extending the search for dark matter WIMPs beyond CDMS-II with SuperCDMS SLAC Experimental Seminar November 17, 2004 Blas Cabrera CDMS Collaboration At Stanford: Paul Brink, Laura Baudis (now at U Florida), Jodi Cooley, Clarence Chang, Walter Ogburn, Matt Pyle, Daniel Soto, Betty Young (SCU), Pat Castle, Astrid Tomada and Larry Novak

2. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 2 CDMS Collaboration UC Berkeley, Stanford, LBNL, UC Santa Barbara, Case Western Reserve U, FNAL, Santa Clara U, NIST, U Colorado Denver, Brown U, U Minnesota, U Florida, Princeton

3. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 3 Dark Matter WIMPs The Science –Scientific case compelling for dark matter WIMPs both from particle physics side and astrophysics side Galaxy formed in dark matter gravitational potential –Our solar system rotates through swarm of WIMPs 10 9 /cm 2 /s –These would only interact with nuclei not electrons ~ (m N /m e ) 2 –Nearly all backgrounds interact with e’s produced by gammas CDMS II detectors and program –Tower 1 (4 Ge and 2 Si detectors) at SUF (neutron limited) –Same Tower 1 at Soudan - PRL 93, 211301 (2004) best by x4 –Towers 1& 2 (2004) and Towers 1-5 (2005) - x20 (n limited) SuperCDMS detectors and program –Development Project - 5 kg Ge new detectors run at Soudan –Phase A (25 kg Ge) & Phase B (150 kg Ge) run at SNOLab –Can run 1000 kg Ge at SNOLab before neutron limited Conclusions: to succeed need SLAC technical and management experience

4. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 4 time The BIG questions ? What is the Origin of the Universe? What role did Quantum Gravity play in the birth of the Universe? The fabric of Space & Time : Was Einstein right? How did Black Holes form in the early Universe?; Are Gamma Ray Bursts related to Black Holes? What is Dark Matter ? Does Dark Energy really exist? How did Galaxies form? Which came first, Black Holes or Galaxies? How does our star work? Is Life in our galaxy unique? What is the ultimate fate of the Universe?

5. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 5 Expanding universe - simulations and data

6. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 6 Concordance Model of Cosmology Supernovae + Cosmic Microwave Background + Large Scale Structure Great overall success! However raises even more questions about origin of dark energy Dark Energy density Matter density

7. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 7 Composition of the Cosmos WIMPs WMAP best fit

8. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 8 Strong motivation Cosmology –Theory: –Observation: Nuclear Physics: baryons - p, n, e –Theory of formation of H, D, He, Li –Observations: Astronomy: luminous matter –Stars & gas Baryonic dark matter is necessary: MACHOs at most 20% of halo mass Non-baryonic dark matter dominates universe hotcold axions neutrinos monopoles WIMPs X √√√√√√ Supersymmetry LSP  ~1 √ ? X √ best DM candidates 0.010.11 But favored by supernova data

9. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 9 The Signal and Backgrounds 00 v/c  7  10 -4 Nucleus Recoils E r  10’s KeV phonons Signal (WIMPs) ErEr  v/c  0.3 Electron Recoils Background (gammas) ErEr ionization Surface electrons from beta decay can mimic nuclear recoils Neutrons also interact with nuclei, but mean free path a few cms

10. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 10 Direct Detection of Neutralinos [e. g., Lewin & Smith; and Jungman, Kamionkowski & Griest] The observed differential rate of events is given by For a Maxwell distribution of incident velocities

11. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 11 To compare the coherent rates of different materials We define the fundamental WIMP-nucleon cross section Two target materials such as Si and Ge very powerful neutron background Spin independent scalar cross section

12. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 12 Nuclear form factor suppression For spin-independent or coherent interactions the form factor F 2 (Q) suppression is shown below and results in suppressed rates for heavy nuclei 50 keV true nuclear recoil threshold is equivalent to about 5 keVee recoil

13. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 13 Summary and bold future vision Limit at SUF 2002 (during CDMS II) Development Project 5 kg of Ge 2008 SuperCDMS Phase C 1000 kg of Ge World-best limit today SuperCDMS Phase A 25 kg of Ge 2011 CDMS II goal 2006 SuperCDMS Phase B 150 kg of Ge 2014

14. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 14 CDMS ZIP Detectors (Ge/Si) Phonon sensors (4) (TES) Ionization Electrodes (2) x-y-z imaging: from timing, sharing WIMPs:  (Ge) >>  (Si) Neutrons:  (Ge)   (Si)

15. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 15 380  m Al fins 60  m wide ~25% QP collection eff. oTES’s patterned on the surface measure the full recoil energy of the interaction oPhonon pulse shape allows for rejection of surface recoils (with suppressed charge) o4 phonon channels allow for event position reconstruction ZIP detector phonon sensor technology

16. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 16 The ZIP Detector Signal Charge & Phonon signals occur on a similar timescale Phonon pulse time of arrival allows for event position reconstruction 20 keV event in a Si & Ge ZIP Si ZIPGe ZIP (EXCELLENT S/N FOR 20 KeV TRUE RECOIL ENERGY)

17. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 17 Am 241 :  14, 18, 20, 26, 60 kev Cd 109 + Al foil :  22 kev ZIP Phonon Position Sensitivity Delay Plot AD CB

18. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 18 First operate at SUF (17 mwe) At SUF –17 mwe –0.5 n/d/kg At Soudan –2090 mwe –0.8 n/y/kg At SNOLab –6060 mwe –1 n/y/ton Log 10 (Muon Flux) (m -2 s -1 ) Depth (meters water equivalent)

19. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 19 ZIP 1 (Ge) ZIP 2 (Ge) ZIP 3 (Ge) ZIP 4 (Si) ZIP 5 (Ge) ZIP 6 (Si) SQUID cards FET cards 4 K 0.6 K 0.06 K 0.02 K The shallow Stanford Underground Facility (SUF) Tower 1 operated at SUF during calendar 2002 at a depth of 17 mwe sufficient to eliminate the hadronic component of cosmic rays

20. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 20 Recoil [keV] vs Charge [keVee] Yellow 252 Cf Blue µ coin Red µ anti

21. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 21 Tower 1 (4 Ge and 2 Si detectors) at SUF SUF Run 21 –Calendar 2002 –52.6 kg-d of Ge after cuts Saw 19 nuclear recoils –clean separation of gamma & beta events –See 10 keV and 67 keV lines for energy calibration All consistent with neutrons –Consistent ratio of Ge singles to Ge multiples –Consistent ratio of Ge events to Si events –Only gain as sqrt(MT) TO DO BETTER NEED TO GO DEEPER

22. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 22 Now operate at Soudan (2090 mwe) At SUF –17 mwe –0.5 n/d/kg At Soudan –2090 mwe –0.8 n/y/kg At SNOLab –6060 mwe –1 n/y/ton Log 10 (Muon Flux) (m -2 s -1 ) Depth (meters water equivalent)

23. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 23 Outside of the Experiment plastic scintillators outer polyethylene lead ancient lead inner polyethylene

24. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 24 Run 118 (1T) & Run 119 (2T) in Soudan

25. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 25 Phonon energy (prg) in keV Excellent agreement between data and Monte Carlo Energy calibration of Ge ZIP with 133 Ba source Ionization energy in keV

26. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 26 Nuclear recoil calibration of Ge & Si ZIPs with 252 Cf Nuclear recoils in Ge ZIP Nuclear recoils in Si ZIP Excellent agreement between data and Monte Carlo

27. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 27 252 Cf Neutron & Gamma calibration data Upper red dashed line are +/- 2  gamma band Lower red dashed line are +/- 2  nuclear recoil band Separate high statistics calibrations with 133 Ba gamma source Determined with calibration data as was the analysis threshold energy

28. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 28 133 Ba gamma & 252 Cf neutron calibrations Use phonon risetime and charge to phonon delay for discrimination of surface electrons “betas” Cuts and analysis thresholds determined entirely from calibration data with WIMP search data blinded until after the cuts and thresholds were set. gammas neutrons ejectrons

29. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 29 Example of setting cut with calibration Calibration - Gaussian distribution 1000 evts Data - same distribution 100 evts Data x10 Cal x10 Cut at last event Probability 0.1 of event past cut On average area beyond last event = 1 On average area beyond cut = 0.1

30. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 30 In 92 days between October 11, 2003 and January 11, 2004, we collected 52.6 live days - a net exposure of 22 kg-d after cuts Below data are shown before (left) and after (right) timing cuts WIMP search data with Ge detectors (yellow points are from neutron calibration)

31. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 31 CDMS-II Reach with five Towers We have begun to explore MSSM cross section range DAMA largely ruled out for spin independent scalar interactions (see Gelmini & Gondolo hep-ph/0405278) Light mass region suggested by Bottino (hep- ph/0307303) largely ruled out Another factor of 3-5 improvement at Soudan past CDMS-II (neutrons) THEN MUST GO DEEPER - exploring SNOLab in Canada EGRET gammas as DM annihilation astro-ph/0408272

32. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 32 Cryocooler Improvements Sumitomo (SHI) RDK415D cryocooler head & compressor 1.5 W at 4.2 K 45 W at 50 K Cost $50k First use in dewar (reduce boiloff) Second use in Estem (colder 4 K stage)

33. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 33 Now installing Towers 3, 4 and 5 in Soudan

34. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 34 Completed fabrication & testing of T3-5

35. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 35 Propose to operate at SNOLab (6060 mwe) At SUF –17 mwe –0.5 n/d/kg At Soudan –2090 mwe –0.8 n/y/kg At SNOLab –6060 mwe –1 n/y/ton Log 10 (Muon Flux) (m -2 s -1 ) Depth (meters water equivalent)

36. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 36 SuperCDMS Roadmap to SNOLAB

37. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 37 Possible SLAC roles At Stanford we know how to fabricate detectors for 25 kg experiment, but for 150 kg and 1000 kg we need to mass produce the fabrication/mounting SLAC could take central responsibility for fabrication with a combination of in house facilities (radon suppression) and commercial production. Other major areas include electronics (custom boards), DAQ (with digitizers for 10k channels readout at a 50 Hz for calibrations), computing (first pass data reduction, data analysis and Monte Carlo simulations). With Spokesperson for SuperCDMS at Stanford, SLAC could & should take the lead role in project management

38. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 38 Detector development (Paul) Existing ZIPs 3” dia x 1 cm thick Thicker ZIPs 3” dia x 1” thick (base detector) Explore larger ZIPs to 4” dia and up to 4 cm thick

39. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 39 Detector development plans

40. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 40 Interleaved Ionization electrodes concept Alternative method to identify near-surface events –Phonon sensors on both sides are virtual ground reference. –Bias rails at +3 V connected to one Qamp –Bias rails at -3 V connected to other Qamp –Signals coincident in both Qamps correspond to events drifted out of the bulk. –Events only seen by one Qamp are < 1.0 mm of the surface.

41. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 41 Interleaved Ionization electrode design Design details –To maintain ~60 pF of capacitance requires keeping bias and ground rails ~ 1 mm apart. –Phonon sensors ‘contained’ within the (200  m wide) ground rails. –First mask-layout recently completed: Ground ring around side to define the ‘Qouter’ volume containing all surfaces

42. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 42 New Read-out schemes Two-stage SQUIDs for reading out new phonon sensors –Allows lower R n, more TESs, better phonon sensor surface area coverage. Will improve effectiveness of present phonon risetime cut even further. –Allows move to Al-Mn TESs to overcome W Tc variability Resitivity of Al-Mn < W, hence risk /design constraint of electro-thermal oscillation if change-over to two-stage SQUIDs not implemented. –Commensurate with NIST-style time-domain multiplexing. ZIP detector phonon pulses are probably sufficiently slow to utilize this scheme effectively to reduce the readout wiring to room temperature that would otherwise be required.

43. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 43 Two-stage SQUID configuration –Ionization detector transformer-coupled to first-stage SQUID –Eliminate potential microphonic read-out issues associated with FET readout –Eliminate IR photon leakage –Eliminate heated FET load on 4 K –Transformer ~ 12 mm x 6 mm chip, fabricated at NIST. –Critically damped circuit, ~1 MHz sampling required. –Simulations give 0.4 keVee FWHM Ionization read-out using SQUIDs

44. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 44 How to build a 1000 kg experiment in stages

45. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 45 Schematic of new ‘SNObox’ x3 Exploring cryocooler system with little or no cryogen servicing

46. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 46 Summary and bold future vision Limit at SUF 2002 (during CDMS II) Development Project 5 kg of Ge 2008 SuperCDMS Phase C 1000 kg of Ge World-best limit today SuperCDMS Phase A 25 kg of Ge 2011 CDMS II goal 2006 SuperCDMS Phase B 150 kg of Ge 2014

47. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 47 Conclusion Excellent scientific reach for 1000 kg Ge experiment at SNOLAB with three phases SuperCDMS Development Project continues to run Towers 1-5, develops 0.6 kg ZIP detectors, and operates one SNOLAB Tower at Soudan in 2008 Start SNOLAB installation in 2007 so that detectors can be operated starting in 2009 SLAC could & should take leadership role in SuperCDMS

48. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 48 Identify and Reduce 210 Pb, 14 C & 40 K Use Van de Graaff to attract positive ion radon daughters 222 Rn -> 218 Po -> 214 Pb -> 214 Bi -> 214 Po -> 210 Pb Run VdG for 2 hrs Wipe surface & count 3.8d3.1m27m20m.16ms 250kV ground

49. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 49 Quantum Universe Question 6: –WHAT IS DARK MATTER? –HOW CAN WE MAKE IT IN THE LABORATORY? “… We need to study dark matter directly by detecting relic dark matter particles in an underground detector and by creating dark matter particles at accelerators, where we can measure their properties and understand how they fit into the cosmic picture.”

50. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 50 Quantum Universe - CDMS!

51. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 51 Quntum Universe - direct detection “… The particle nature of dark matter can be verified by finding the rare events they would produce in a sensitive underground dark matter detector such as CDMS. …” “However, to understand the true nature of dark matter particles, particle physics experiments must produce them at accelerators and study their quantum properties. Physicists need to discover how they fit into a coherent picture of the universe. Suppose experimenters detect WIMPs streaming through an underground detector. What are they? Are they the lightest supersymmetric particle? The lightest particle moving in extra dimensions? Or are they something else?” Did not go the final step of saying that if supersymmetry discovered at an accelerator then we must see if it is the dark matter with direct detection experiments.

52. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 52 Earlier MSSM Baltz & Gondolo PRD67 065503 (2003) Kim,Nihei,Roszkowski, hep-ph/0208069 Baltz & Gondolo hep-ph/0102147

53. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 53 mSUGRA and relax GUTs Baer et al, hep-ph/0305191 Chattopadhyay et. al, hep-ph/0407039 Ellis et al, hep-ph/0306219 Bottino, et al hep-ph/0307303

54. Blas Cabrera - Stanford UniversitySLAC Experimental SeminarPage 54 mSUGRA and Split Supersymmetry Baltz & Gondolo hep-ph/0407039 A. Pierce, hep-ph/0406144 & G. F. Giudice and A. Romanino hep-ph/0406088