1. Results from the Cryogenic Dark Matter Search Using a  2 Analysis Joel Sander December 2007

2. First Evidence for Dark Matter Fritz Zwicky’s 1933 observation of the Coma cluster using the virial method Measured the radial velocity of 8 galaxies Implied gravitational force 400 times greater than expected from luminosity Accurate value of the Hubble constant would have changed discrepancy to a factor of 50 Believed there was unobserved matter “dunkle kalte Materie” or dark cold matter M vir = 2  2 v vir /G N Andromeda In 1970, Rubin showed the rotational v r (r) = const. for the Andromeda galaxy

3. Clusters Mass of luminous matter estimated from cluster luminosity & mass-light ratios Total cluster mass is measured by: – Virial method – X-ray – Gravitational Lensing Coma Cluster - Xray T y(w) =8(10)keV, R vir = 1.8h -1 Mpc 27.1 o 28.6 o 195.4 o 194.1 o Gravitational pressure balanced by gas pressure: Assuming n % r -2 : = 1.4x10 15 h -1 M o In agreement with the virial est. p=nk B T.

4. Cosmic Microwave Background Light from decoupling of photons and baryons in the early (z~10 3 ) nearly isotropic and homogeneous universe CMB Photons travel to us from the equidistant surface of last scattering Observations described by a blackbody spectrum with T 0 = 2.725K Initial small fluctuations lead to potential wells, causing small temperature fluctuations Size and intensity of the fluctuations are sensitive to early state of the universe Roughly speaking,  ~ 2/ l WMAP only assuming  CDM model

5. Universe Budget: Mostly Unidentified Data from Supernovae, CMB, and Clusters in agreement! Significant dark matter required. But what kind of dark matter? WMAP, SDSS, and Supernova mm bb  kk

6. Weak-Scale Structure Formation ← Growth with no dark matter ← Current Size of fluctuation R – time of decoupling Weakly Interacting Massive Particles (WIMPs) provide an explanation for the observed structure

7. Dark Matter Around Here?

8. Is it possible to detect WIMP interactions? Energy deposited, E r Rate –Cross section –Flux on detector Backgrounds Assumptions – Local WIMP density  W = 0.3 GeV/c 2 – Local galactic velocity: v = 220 km/s = 0.7x10 -3 c WIMP Interactions

9. v/c =   0.7  10 -3 Direct Detection: Recoil Experiment WIMP We use Germanium, A=73; others: Si, I, Xe, W v/c =   0.7  10 -3 E R   2 v 2 /m Ge  40 2  (0.7  10 -3 ) 2 / 73  10 keV  x-ray energy! Easy! Sun moves with V~ 220km/sec through the Dark Matter halo

10. Donald H. Perkins, 1987 What is the Rate of Interactions? Rate = 5 x 10 -9 [kg day] -1 Ouch! R = N  = (8x10 24 atoms/kg) (6x10 9 cm -2 day -1 )  = 5x10 34  [cm 2 ] recoils/kg/day

11. The Cross Section Calculating the transition rate from Fermi’s golden rule and equating with  v gives: It is useful to express  relative to the cross section on a single nucleon,  1 … assuming  1 2 = 1 and F 2 (q 2 ) = 1, we have: r2A2r2A2. I  =. r2A2r2A2 I r2A21r2A21     r 2 A 2 [cm 2 ] For massive WIMPs, cross section proportional to A 4 ! . 10 -36 [cm 2 ] … 100GeV WIMP on Ge R = 0.05 recoils / kg / day … still low, but possible to detect

12. Calculating  in CM Frame - 1 p = |p f | = |p i |=  r v, where v =  | v f – v i | 1 2 (2  ) 3 (2  ) 3 (2  ) 3 2. d 3 p p 2 dpd  p  r dEd  ==dN = 1. = A f F(q), assuming f p = f n = =>

13. The Form Factor The form factor accounts for the structure of the nucleus It is given by the Fourier transform of the nuclear wavefunction F(q=0) = 1. Helm form factor:

14. Calculating  in CM Frame - 2 1 2 ( AfF(q) ) 2 = v d  => or It is useful to express  relative to the cross section on a single nucleon,  1 … assuming  1 2 = 1 and F 2 (q 2 ) = 1, we have: r2A2r2A2. I  =. r2A2r2A2 I r2A21r2A21     r 2 A 2 [cm 2 ] For massive WIMPs, cross section proportional to A 4 ! . 10 -36 [cm 2 ] … 100GeV WIMP on Ge

15. Estimating the Rate R = N  = (8 x 10 24 [Ge atoms/kg] ) (10 -36 [cm2] ) (6x10 9 [cm-2 day-1] ) = 0.05 recoils / kg / day … still low, but possible to detect Can make a more realisitic estimate of the differential rate (per unit detector mass) by assuming a more realistic halo model, f(v):  d  = dR = … using dE r = d|q| 2 / 2m N and

16. The Form Factor The form factor accounts for the structure of the nucleus It is given by the Fourier transform of the nuclear wave function F(q=0) = 1. Helm Form Factor approximates nucleus as: s   0 : core with constant density and radius, R. 1.2A 1/3 fm   1 : surface with thickness of.1fm,  1 % e -r 2 /2s 2, s. 0.9fm   0 and  1 normalized:

17. Estimating the Rate R = N  = (8 x 10 24 [Ge atoms/kg] ) (10 -36 [cm2] ) (6x10 9 [cm-2 day-1] ) = 0.05 recoils / kg / day … still low, but possible to detect --- Ignoring the form factor | Including the form factor  1 assumed to be 10 -42 cm 2 Assuming a halo with a Maxwellian velocity distribution with a velocity dispersion of 220km/s:

18. Rate of Main Background Rate about 20 / (kg-day) ! Strategies: shield and distinguish electron recoils from nuclear recoils Shield it! 40 K: 7x10 4  /day 1m

19. Backgrounds: Like an Onion Peel back one background, and you find another background! Background Method of Removal Gammas Shield Reject – Analysis Neutrons Shield Veto Surface Events Reject - Analysis Will discuss now. Will discuss later after describing the detectors.

20. Shielding Gammas Low Activity Lead µ-metal (with copper inside) Ancient lead 23cm Use passive shielding to reduce  rate to Ge:~131 K2 events / kg / day Si: ~ 548K5 events / kg / day (from 15-45keV) Lead and Copper for gammas Inner lead layer from Roman shipwreck

21. Ionization Inner and Outer electrode to reject events near edge Z-sensitive Ionization Phonon Detector Q inner Q outer D C A B R sh I bias SQUID array Phonon A R feedback V qbias Z-dependent Ionization and Phonon-mediated z y x @50 mK 250g Ge (100g Si) 1 cm thick x 7.6 cm dia. Inner/Outer electrodes Four phonon sensors X-Y-Z Information Photolithographic patterning Phonon Sensors

22. R0R0 RR TT T0T0 380  m 60  m Al Al Collector W Transition Edge Sensor (TES) Ge or Si phonons Cooper Pair Sensors held in equilibrium between Normal and Super Conducting. Highly sensitive to small energy deposit. Fast signal. SQUID Readout

23. Excellent Energy, Position Resolution Am 241 :  14, 18, 20, 26, 60 kev Cd 109 + Al foil :  22 kev Cd 109 :  22 kev i.c. electr 63, 84 KeV Detector Calibration at Berkeley

24. Energy Resolution DetectorMean (keV)  (keV) Mean (keV)  (keV) T1Z110.581.0110.400.44 (1.34) T1Z210.370.5010.300.30 (0.78) T1Z310.430.3210.910.26 (0.61) T1Z510.430.3710.340.32 (0.74) T2Z310.290.4410.280.29 (0.73) T2Z510.170.3910.050.61 (1.28) IonizationPhonon Use the 10.36keV line from 71 Ge decay (100% EC) to examine the energy resolution T1Z2 - Ionization dN/dE T1Z2 - Phonon dN/dE DetectorWidth (keV) T1Z25.6 T1Z54.2 T2Z32.9 T2Z5NA 67keV line

25. CDMS Towers of Detectors 6 Detectors Per Tower –0.25kg (0.10kg) per Ge (Si) detector –Livetime of 74.58 days – 2 Tower results published – Will describe simultaneous, parallel, blind analysis –neutron and  (open & closed ) calibration data Each tower holds 6 ZIPs ZIP 1 (Ge) ZIP 2 (Ge) ZIP 3 (Si) ZIP 4 (Ge) ZIP 5 (Si) ZIP 6 (Ge) Tower 1 Cold Electronics Tower 2Tower 1

26. Detection: Signal and Background  0 (calibrate: neutron)   7  10 -4 Nucleus Recoils dense energy deposition Poor Ionization Efficiency Signal ErEr    0.3 Electron Recoils Background Sparse Energy Deposition Excellent Ionization Eff. ErEr Recoil Differences give Particle Identification

27. Excellent Primary (  ) Background Rejection Yield=Ionization/Phonon  source: Electron Recoil N source: Nuclear Recoil Phonon Energy (keV) Neutrons cause nuclear recoils too! Another background… Yield = Ionization/Phonon Most effective Particle ID Radioactive source data defines the signal (NR) and background (ER)

28. Phonon Energy is the true measure of the recoil energy Shutt et al., 1992 Nuclear recoils (induced by a neutron source) Electron recoils (induced by a  source) Ionization Phonons =1 (bkgd)  1/3 (sig) Excellent Primary (  ) Background Rejection Yield / Ionization / Phonon Energy Calibration Data

29. The Analysis List of Cuts: o Data Quality Cuts Reject Obviously Bad Data Higher Standard for Potential WIMP interactions o Analysis Regime o Fiducial Volume Cut o Ionization Threshold Cut o Single Scatter Cut o Nuclear Recoil Band Cut o Veto Anti-coincidence Cut o Timing Outlier Cut o Surface Event Rejection Cut Will discuss with rejection of gamma bkg. (Now) Will discuss with neutron bkg. Will discuss with surface event bkg.

30. Rejecting Bad Events Bad Detectors, T1Z1, T1Z6, and T2Z1 5 (4) remaining good Ge (Si) detectors Data taken after a power outage Spike in event rate after a pump trip Data taken during cryogen transfer Failed Kolmogorov-Smirnov (KS) - test Other (wrong Q-bias, missing global trigger, etc) T1Z1 (Ge): high T c -> uneven detector response and increased number of background events (T1Z1 was first detector fabricated) T1Z6 (Si): known contamination with 14 C T2Z1 (Si): earlier test data & in situ calibration data indicate poor signal-to-noise in 2 phonon channels WIMP-search data: 5.23 million potential interactions

31. Higher Standard for Potential WIMPs WIMP-search data: 4.54 million potential interactions Y-delay (  s) Ionization Energy T2Z5 Events with abnormal ionization pulses are removed Events with phonon activity preceding the event are removed Events with any abnormally negative (6  ) phonon pulse are removed Events within a region of abnormal ionization energy collection are removed

32. Analysis Regime: Threshold Need to determine the low recoil energy analysis threshold (7keV, 20keV for T1Z4) WIMP spectrum falls exponentially (100keV) Don’t want mis-estimation of the ionization energy to allow electron recoils fake nuclear recoils Fit ionization pulses with characteristic white noise Fit ionization pulses using identical  2 minimization as is used for data. (Large pulses are harder to misfit.) Phonon recoil energy threshold chosen such that ~0.1 electron recoils misfit as nuclear recoils expected to be above threshold in WIMP-search data p r = p t – Q1549 events from p r =3keV to 3.5keVmisfit: An ER with Q=3.5keV (p r =3.5keV), misfit to Q=1.75keV: p r =5.25keV,1/400 Q=5keV (p r =5keV), misfit to Q=2.5keV: p r =7.5keV0/20k Y=1/3, nuclear recoil WIMP-search data: 51.4 thousand  calibration data: 526 thousand potential interactions

33. Fiducial Volume Cut Events near the outer surface can have uncollected ionization (and phonon) energy. Require events’ ionization energy to be contained within the inner electrode by requiring ionization energy of outer electrode to be consistent with noise About 82% of detector area covered by the inner electrode QiQi QoQo  calibration data: 327 thousand potential interactions Rejected Accepted

34. Estimating Fiducial Volume Cut Effic. Estimate the fraction of nuclear recoil events from neutron calibration data that pass the fiducial volume cut as a function of phonon recoil energy. Estimate is biased low: – Multiple scatters more likely to fail the fiducial volume cut. – Electromagnetic events near detector surfaces are disproportionately distributed under the outer electrode and can have nuclear recoil-like yields. Use gamma calibration data to estimate rate of surface events faking nuclear recoils that pass/fail the fiducial volume cut Phonon Recoil Energy (keV) Yield

35. Fiducial Volume Cut Efficiency Legend: Method 1 Method 2 Fit to Method 1 Fit to Method 2

36. Ionization Threshold  calibration data: 326 thousand potential interactions 3.85  Count Gammas Nuclear recoils Zero charge Designed to require potential signal events to have an ionization signal ~4  above mean noise event to reject zero- charge events <0.01 zero charge events expected above threshold (~80 zero charge events between 5- 100keV)

37. Ionization Threshold Efficiency Legend: Data -- Threshold Fit to Data

38. Single Scatter Cut  calibration data: 94 thousand potential interactions WIMPs will not scatter in multiple detectors while backgrounds can Rejects events with total phonon energy more than 6  away from the mean in any other detector AcceptedRejected

39. Single Scatter Cut Efficiency Efficiency is only lost when a true single scatter is misidentified as a multiple scatter. The efficiency of the single scatter cut is > 99.9% in all detectors.

40. Yield Plots – Nuclear Recoil Band Yield Plots standard way of showing data  bands and nuclear recoil bands defined using 133 Ba and 252 Cf calibration data Yield / Ionization / Phonon Energy Calibration Data Gamma-induced electron recoil background peeled away. What about the neutron-induced nuclear recoil background?  calibration data: 59 potential interactions

41. Nuclear Recoil Band Efficiency Legend: Data -- Threshold Fit to Data

42. Cosmic Muon Induced Neutron Background Limited earlier result at shallow ( ~ 15mwe)…moved to a deep mine

43. Where? Soudan, Minnesota Enter here Depth of 689m (2341 ft.) underground (2090 mwe) Muon flux 50,000 times less than flux at the surface Depth (meters water equivalent) Kamioka (Japan) 0 2000 4000 6000 8000 10000 3 2 1 0 -2 -3 -4 -5 -6 -7 -8 Soudan Log 10 (Muon Flux) (m -2 s -1 )

44. Polyethylene 41 cm 14 Use passive shielding to reduce /Neutrons Lead and Copper for photon Polyethylene for low- energy neutron Passive Neutron Shielding

45. Muon Veto Neutron-induced nuclear recoil background peeled away. What about the surface event background?  calibration data: 57 potential interactions Surround detectors with active muon veto Reject Veto-coincident events 1 veto coincident multiple scatter nuclear recoil observed Pre-unblinding neutron background estimate: Ge: 0.06 events Si: 0.05 events

46. Efficiency of Veto Cut to Pass WIMPs Need fraction of events with “accidental” veto activity. Rate of events in the muon veto is R = 603K2Hz. Events with veto activity in the preceeding 50  s rejected Efficiency of the Muon Veto Anti-coincidence cut for accepting WIMP-induced nuclear recoils is then: Count /  s Time (ms)

47. Estimating the Neutron Background 1 The expected neutron background is given by: Pull (datathief) tower 1 single scatter recoil spectra from Sharmila’s thesis Fit to recoil spectra Compare with Sharmila’s estimate Account for higher (lower) neutron- induced single scatter nuclear recoil rate in end (interior) detectors ↑ From Sharmila Kamat’s thesis (monte carlo, GEANT) T1Z3 X10 -3 events /kg/day

48. Estimating the Neutron Background 2 Rescale rates (up) to Sharmila’s higher rates Ge: 2.5/2.1=1.2, Si: 8.0/5.1=1.6 Rate from 7-100keV becomes: R Ge = 2.9x10 -3, R Si = 8.6x10 -3 (events/kg/day) Calculate the expected background: Estimate: Ge: B n = 0.03 (0.02) events looser (stricter) analysis Si: B n = 0.03 events X10 -3 events /kg/day

49. Where Surface Events Come From There are three classes of surface events: 1)Ambient gammas that Compton-scatter off electrons in a detector sometimes scatter in the first few microns of a detector. An electron (ejectron) that is scattered near the surface can be ejected from the detector towards an adjacent detector. 2)Electrons Compton-scattered near the detector surface that do not escape the detector. 3)Electrons from beta-decay of radioactive contaminants on detector surfaces. Decays from ambient radon implant 210 Pb less than a micron into the surface of a detector. These classes do not contribute equally to surface events in WIMP- search data and gamma calibration data. Most surface events in calibration data are from classes 1) and 2). Most surface events in WIMP-search data are from class 3).

50. Why Surface Events are Dangerous ↑ Open Gamma Calibration Data Surface events: have incomplete collection of ionization energy have abnormally low yield causing them to droop down from the gamma band and potentially into the nuclear recoil band are a clear background – most/all of the 57 “gamma” remaining events are surface events must be rejected in analysis, but how?

51. Defining a Sample of Surface Events Surface events within a “wide beta” region of open gamma calibration data are used to define a sample of surface events. “wide beta” surface events are used to define criteria for rejecting surface events in WIMP-search data. “wide beta” region contains single and multiple scatter surface events with yield 5  below the mean bulk gamma yield and with a yield > 0.1. Will test the surface event rejection cut on events within the “wide beta” region of closed gamma calibration data.

52. Parameters Used to Reject Surface Events There are 3 parameters are used to reject surface events: A  2 analysis uses these 3 correlated parameters to distinguish between surface events and nuclear recoils. Neutron-induced nuclear recoils from neutron calibration data are used as a surrogate for WIMP-induced nuclear recoils. 1) Phonon Delay – how long after the ionization pulse until the largest phonon pulse reaches 20% of its maximum height. 2) Phonon Risetime – how long it takes for the largest phonon pulse to rise from 10% to 40% of its maximum height. 3) Energy Partition – the ratio of energy deposited in the primary phonon sensor to the energy deposited in the opposite sensor Nuclear recoils Surface events

53. A  2 Analysis Calculate the  2 deviation from the nuclear recoil hypothesis,  n 2, and the surface event hypothesis,  b 2 The values of the 3 surface event rejection parameters have distributions of for nuclear recoils and surface events with a mean,  : Calculate a covariance matrix expressing the correlations between the surface event rejection parameters: The value of  b 2 and  n 2 for the kth event is given by: i – index indicating nuclear recoil hypothesis (i=n) or surface event hypothesis (i=b) j – index indicating which surface event rejection parameter

54.  2 Distributions of Events To pass the surface event rejection cut an event must meet 2 requirements: Must be consistent with the nuclear recoil hypothesis,  n 2 < 10. Nuclear Recoils passing: 0.67K0.01(Ge) / 0.79K0.01 (Si) Surface Events rejected: 0.34K0.01 (Ge) / 0.56K0.02 (Si) A parameter d  2 characterizes whether an event better fits the surface event hypothesis or the nuclear recoil hypothesis. Will choose a value of d  2 using what criteria?  b 2 –  n 2 Count Coadded Germanium

55. Criteria for Choose a Value of d  2 Can set a looser cut to allow more WIMP-induced nuclear recoils or a stricter cut to reject more surface events…how do we balance these? Two strategies that provide a balance are 1) optimizing sensitivity and 2) optimizing discovery potential. –Sensitivity is defined to be the mean upper limit (90% conf.) on the cross-section of WIMP-nucleon interactions. (smaller upper limit - > better sensitivity) –Discovery potential is defined to be the cross-section for which a convincing case for a signal could be asserted. (smaller cross-section -> better discovery potential) Sensitivity varies slowly near the optimum, so we focused on discovery potential while requiring near optimum sensitivity. For silicon detectors will set a cut by eye.  = # of target nuclei / kg = 10 3 N A /A T = SF between  (target nucleus) and  (target nucleon)

56. Sensitivity The number of observed WIMP-induced nuclear recoils, N o, is related to the number of WIMP-induced nuclear recoils: N o =  nr x N i Poisson: ↑ Poisson probability distribution ← 90% confidence upper limit with k observed events Two Methods: No bkg. Subtraction use Poisson Bkg. subtraction use Feldman Cousins

57. Discovery Potential Set Ge value of d  2 for 3  hint of a WIMP signal with 3 observed events Si value of d  2 set by eye o Table of maximum allowed backgrounds. N o =  nr x N i m = 1.25 kg  L = 74.6 days  = # of target nuclei / kg = 10 3 N A /A T = SF between  (target nucleus) and  (target nucleon)

58. Sensitivity and Discovery Potential Chose a surface event rejection cut with 3  discovery potential for 3 observed events. (B < 0.27 events.) Guessed that the neutron background would be 0.1 events. (obviously over estimated the neutron bkg.) (B  < 0.17 events, d  2 = 12) Did not have the plot of sensitivity vs. B at the time, but we knew the cuts were near the optimum. Defined stricter cut with B  < 0.08 events (d  2 = 18). Made stricter cut be the primary surface event rejection cut.  b 2 –  n 2 Count Coadded Germanium

59. Silicon Detectors Values of d  2 chosen  under time pressure  by eye  before deciding to use Si detectors to set a limit Notice that newer Tower 2 silicon detectors have much lower surface event rate! Legend: Nuclear recoils Surface events Surface events passing consistency cut (  n 2 < 10).

60. Stricter Surface Event Rejection Efficiency Legend: Data -- Threshold Fit to Data

61. Looser Surface Event Rejection Efficiency Legend: Data -- Threshold Fit to Data

62. Analysis Efficiency

63. Testing On Closed Gamma Calib. Data Expect 25K5 events (13K4 events for the stricter cut) to pass the cut. Observe 35 events (26) to pass the cut, 1.9  (3.6  ) > than expectation. What happened? Probably due to drift in the experiment. Data was split every 2 hours (open then closed) while the noise environment changes in about 1hr. The noise template was derived from first 500 events and better describes the open gamma calib. noise environment. Resplit the gamma calib. data every other event, found the resplit subsets to be statistically consistent.

64. Expected Surface Event Background Background measured from WIMP-search sidebands (“wide beta” – 3  NR band single scatters) and the closed gamma calibration data (all “wide beta” events) – Gamma calibration: better stats – WIMP-search: surface event sample in situ, surface events from same source <- better The number of surface events passing the cut are scaled to expected number of 2  nuclear recoil band single scatters in WIMP- search data Scalings determined using data prior WIMP- search run Closed  WIMP-Search: Estimate from Closed  calibration Ge Stricter 0.16 +0.08 (10-100keV) Ge Looser 0.21 +0.11 (10-100keV) -0.07 -0.09 Estimate from WIMP-Search Sidebands

65. Estimation of Systematics 64020T2Z5 11000T2Z3 55000T1Z5 00000T1Z3 10100T1Z2 TotalFiducial Volume Shifted  T2Z5 CliffYield (Upper)Detector =13 x S 4 = 0.4 events Stricter Cut: 108020T2Z5 22000T2Z3 76100T1Z5 22000T1Z3 10100T1Z2 TotalFiducial Volume Shifted  T2Z5 CliffYield (Upper)Detector =22 x S 4 = 0.6 events Looser Cut: Estimate from WIMP-Search Sidebands

66. Estimation of Systematics Upper Yield – change “wide beta” upper yield cutoff from -5  to -4.5  to estimate the effect on the background estimate of gamma leakage into “wide beta” region – no effect T2Z5 Cliff Cut – Allow all events within the region of abnormal ionization energy – 2 events Shifted Means – the mean values of the surface event rejection parameters are different in WIMP-search data and  calibration data. Shifting the  2 b and  2 n values accordingly – 2 (1) event Fiducial Volume – Increase allowed region to: 0.85 < (Q i –Q o )/(Q i +Q o ) < 1.15 – 10 (18) events

67. What Expectations? Assuming cross section of 10 -42 cm 2 (normalized to a single nucleon) and assuming standard (simplistic) halo parameters

68. The Ge Result I Pass all cuts except the surface event rejection cut o Also pass looser cut o Also pass stricter cut WIMP-Search Closed  & neutron calib. neutrons from calibration data “wide beta” surface events “wide beta” surface events passing the looser surface event rejection cut

69. The Ge Result II Pass all cuts except the surface event rejection cut o Also pass looser cut o Also pass stricter cut neutrons from calibration data “wide beta” surface events “wide beta” surface events passing the looser surface event rejection cut

70. The Ge Result III Pass all cuts except the surface event rejection cut o Also pass looser cut o Also pass stricter cut neutrons from calibration data “wide beta” surface events “wide beta” surface events passing the looser surface event rejection cut near miss event No WIMP-induced nuclear recoils observed! Set a limit.

71. The Si Result I Pass all cuts except the surface event rejection cut o Also pass looser cut o Also pass stricter cut neutrons from calibration data “wide beta” surface events “wide beta” surface events passing the looser surface event rejection cut

72. The Si Result II Pass all cuts except the surface event rejection cut o Also pass looser cut o Also pass stricter cut neutrons from calibration data “wide beta” surface events “wide beta” surface events passing the looser surface event rejection cut 1 event within 2  nuclear recoil band One potential WIMP-induced nuclear recoil observed, consistent with background. Set a limit.

73. Ionization Yield time (hours) Automatic LED flash to re-neutralize detectors Ba calibration for comparison Candidate The Ge Event Observed by Other Analyses

74. A Limit Legend: --- Prior result at Soudan This Ge result (-.-. looser) Combined result This Si result Edelweiss (2005) DAMA low mass allowed region (90% conf.) (Gondolo & Gelmini 2005) An MSSM region (Kim et. al. 2002)

75. Comparing Limits

76. What’s Next? 5 tower run underway, data currently being analyzed Detectors with lower rates of surface event Better analysis techniques Leading to: ?

77. The CDMS Collaboration I

78. Remote Data Acquisition

79. Stanford University P.L. Brink, B. Cabrera, C.L. Chang, J. Cooley, R.W. Ogburn, M. Pyle, S.Yellin University of California, Berkeley M. Daal, J. Filippini, A. Lu, V. Mandic, P.Meunier, N. Mirabolfathi, B. Sadoulet, D.N. Seitz, B. Serfass, K.M. Sundqvist University of California, Santa Barbara R. Bunker, D.O. Caldwell, R. Ferril, R. Mahapatra, H. Nelson, J. Sander, University of Colorado at Denver and Health Sciences Center M. E. Huber University of Florida L. Baudis, S. Leclercq University of Minnesota P. Cushman, L. Duong, A. Reisetter Brown University M.J. Attisha, R.J. Gaitskell, J-P. F. Thompson Case Western Reserve University D.S. Akerib, C. Bailey, P. Brusov, M.R. Dragowsky, D.D.Driscoll, D. Grant, R. Hennings-Yeomans, S.Kamat, T.A. Perera, R.W.Schnee, G.Wang Fermi National Accelerator Laboratory D.A. Bauer, M.B. Crisler, R. Dixon, D. Holmgren, E.Ramberg, J. Yoo Lawrence Berkeley National Laboratory R. McDonald, R.R. Ross, A. Smith National Institute for Standards and Technology K. Irwin Santa Clara University B.A. Young Cryogenic Dark Matter Search The CDMS Collaboration II