First CDMS II Five-Tower Results. Sunil Golwala SLAC Summer Institute 2008 August 7, 2008

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1 First CDMS II Five-Tower Results Sunil Golwala SLAC Summer Institute 2008 August 7, 2008

2 Overview Why and how do we look for WIMP dark matter? Candidate WIMPs from particle physics The Cryogenic Dark Matter Search II (CDMS II) experiment Analysis of first CDMS II five-tower data set and WIMP-search results Plans for the future SLAC Summer Institute 2008/First CDMS II Five-Tower Results 2

the form of dark energy, a fluid that has negative pressure (causes the universe s expansion to accelerate) and does not clump gravitationally, ΩDE = ρde/ρcrit = 0.76±0.

3 Why Dark Matter? A host of astronomical and cosmological observations indicate: Total energy density = critical density ρcrit needed for spatially flat universe (within errors) The bulk is in the form of dark energy, a fluid that has negative pressure (causes the universe s expansion to accelerate) and does not clump gravitationally, ΩDE = ρde/ρcrit = 0.76±0.05 Most of the matter is in the form of dark matter, matter that interacts gravitationally but not electromagnetically, ΩDM = ρdm/ρcrit = 0.20±0.03 The remaining matter is in the form of baryons, ΩB = ρb/ρcrit = 0.042±0.004 (though most of this has not yet been directly observed!) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 3

4 Required Dark Matter Characteristics Dark matter must have two important characteristics to satisy observations Cold/warm (not hot): must be nonrelativistic at the time of matter-radiation equality (z ~ 3500) in order to collapse gravitationally and seed the large-scale structure we see. M < kev (e.g., neutrinos) is hot and not allowed at significant levels. Nonbaryonic Light element abundances + Big Bang Nucleosynthesis fix baryon density; we need more matter than is allowed in baryons Baryonic matter would not be able to begin collapse until recombination (z ~ 1100) due to coupling to photon plasma Locally, dark matter must have the following characteristics: density ~ 0.3 GeV/cm 3 : 1 proton/3 cm 3, 1 WIMP/coffee cup velocity: simplest assumption is Maxwell-Boltzmann distribution with σv 220 km/s SLAC Summer Institute 2008/First CDMS II Five-Tower Results 4

5 Weakly Interacting Massive Particles A WIMP δ is like a massive neutrino: produced when T >> m δ via pair annihilation/ creation. Reaction maintains thermal equilibrium. If interaction rates high enough, comoving density drops as exp( m δ / T) as T drops below m δ : annihilation continues, production becomes suppressed. But, weakly interacting will freeze out before total annihilation if canonical Kolb and Turner freeze-out plot H > Γ ann σ ann v i.e., if annihilation too slow to keep up with Hubble expansion Leaves a relic abundance: Ω δ h 2 n δ σ ann v fr cm 3 s 1 for m δ = O(100 GeV) if m δ and σann determined by new weak-scale physics, then Ω δ is O(1) freeze out SLAC Summer Institute 2008/First CDMS II Five-Tower Results 5

Supersymmetry: solves gauge hierarchy problem improves coupling unification Neutralino LSP δ mixture of bino, wino, higgsinos; spin 1/2 Majorana particle Allowed regions Supersymmetric WIMPs bulk: δ

6 Supersymmetry: solves gauge hierarchy problem improves coupling unification Neutralino LSP δ mixture of bino, wino, higgsinos; spin 1/2 Majorana particle Allowed regions Supersymmetric WIMPs bulk: δ annih. via t-ch. slepton exchange, light h, high BR(b sγ) and (g-2)µ; good DD rates stau coann: δ and stau nearly degenerate, enhances annih., low DD rates bulk focus point: less fine-tuning of REWSB, δ acquires higgsino component, increases annih. to W, Z, good DD rates A-funnel: at high tan β, resonant s-ch. annih. via A, low DD rates χ 2 of fit to BR(b sγ), muon g-2, and relic density (dominated by relic density: avoid overclosure) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 6 stau coannihilation A-funnel (at high tan β) focus point predictions! Baer et al, in DMSAG report

7 Direct Detection: Signature δ WIMPs collected in spherical isothermal halo: ideal gas with gravity, kt = mv 2 /2, v km/s WIMPs elastically scatter off quarks in target H,h,Z nuclei, producing nuclear recoils, with σqδ related to σann (same diagrams: via Z, h, H, and squarks) q Energy spectrum of recoils ( is ) exponential, ER ~ 50 kev, depends on WIMP and target masses: Boltzmann distribution (spherical isothermal halo) + NR s-wave scattering E 0 = 2 m2 δ m N (m δ + m N ) 2 v2 0 m N 50 kev 106 Amplitude of recoil energy spectrum, i.e. event rate, normalized by σnδ, local WIMP number density, and nucleus-dependent A 2 F 2 (ER): dr de R n δ σ nδ E 0 exp ( E R E 0 At low ER, scattering is coherent and A 2. Coherence lost at larger ER via form factor F 2 (ER) ) A 2 F 2 (E R ) δ q I/Xe δ q Ge ( WIMP flux ~10 5 /cm 2 /sec E 1 δ s-wave scattering ( q ~ E δ exp Si δ q ( E ) δ kt SLAC Summer Institute 2008/First CDMS II Five-Tower Results 7

3 Sparse Energy Deposition δ Neutrons same, but σ 10 20 higher; must shield (go

8 Nuclear Recoil Discrimination Signal Background Nuclear Recoils Er v/c 10-3 Dense Energy Deposition Electron Recoils Er v/c 0.3 Sparse Energy Deposition δ Neutrons same, but σ higher; must shield (go deep underground) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 8 γ Density/Sparsity: Basis of Discrimination

Nuclear Recoil Discrimination in CDMS Recoil energy Phonon (acoustic vibrations, heat) measurements give full recoil energy Ionization yield ionization/recoil energy strongly dependent on type of

9 Nuclear Recoil Discrimination in CDMS Recoil energy Phonon (acoustic vibrations, heat) measurements give full recoil energy Ionization yield ionization/recoil energy strongly dependent on type of recoil (Lindhard) Excellent yield-based discrimination for photons 2 x 10-4 misid bulk electron recoils (gamma source) bulk nuclear recoils (neutron source) X surface electron recoils (NND selection) Ionization dead layer: low-energy electron singles (all surface ER): 0.2 misid 1.2 x 10-3 of photons are surface single scatters, 0.2 of those misid d ( 2 x 10-4 ) But, phonon timing identifies surface events w/ < 0.01 misid, giving Photons: < 2 x 10-6 misid Single-scatter low-energy electrons: < 2 x 10-3 misid SLAC Summer Institute 2008/First CDMS II Five-Tower Results 9

10 CDMS ZIP Detectors Z-sensitive Ionization- and Phononmediated detectors: Phonon signal measured using photolithographed superconducting phonon absorbers and transition-edge sensors. R [!] TES = transition edge sensor T [mk] SQUID array Phonon D qp-trap I bias R bias R feedback! D A quasiparticle diffusion C B Al W Si or Ge crystal V qbias Q outer Q inner athermal phonons propagate ballistically SLAC Summer Institute 2008/First CDMS II Five-Tower Results 10

11 1 µm tungsten TES 380 µm x 60 µm aluminum fins CDMS ZIP Detectors Z-sensitive Ionization- and Phononmediated detectors: Phonon signal measured using photolithographed superconducting phonon absorbers and transition-edge sensors. R [!] TES = transition edge sensor T [mk] SQUID array Phonon D qp-trap I bias R bias R feedback! D A quasiparticle diffusion C B Al W Si or Ge crystal V qbias Q outer Q inner athermal phonons propagate ballistically SLAC Summer Institute 2008/First CDMS II Five-Tower Results 10

12 tion measurement %,#$%$-.-/0'(+s in 3 ld 1 µm tungsten TES I bias R bias D A Two ionization C channels: B! Inner fiducial volume CDMS ZIP Detectors Z-sensitive Ionization- and Phononmediated detectors: Phonon signal measured using photolithographed superconducting phonon absorbers and transition-edge sensors. Ionization measurement 380 µm x 60 µm aluminum fins! %,#$%$-.-/0'(+e - and "#$%$&'()*+$ h + drift to surfaces in 3 SQUID or 4 array V/cm applied field Inner electrode (85%) R feedback! Outer electrode where field lines are not uniform Outer electrode V qbias (15%)! Phonon D FET amp Q outer Q inner "#$%$&'()*+$ quasiparticle diffusion Two Al ionization channels: T [mk] qp-trap SLAC Summer Institute 2008/First CDMS II Five-Tower Results 10 R [!]! Inner fiducial volume! Outer electrode where field lines are not uniform 3 2 1! TES = transition edge sensor FET amp W Si or Ge crystal athermal phonons propagate ballistically

13 ZIP xy Position Sensitivity Speed of sound in Si (Ge) ~ 1 (0.5) cm/µs A Delay Plot D Am 241 : γ 14, 18, 20, 26, 60 kev AD-BC delay [µs] Cd 109 : γ 22 kev i.c. e 63, 84 kev B C Cd Al foil : γ 22 kev CD-AB delay [µs] SLAC Summer Institute 2008/First CDMS II Five-Tower Results 11

14 ZIP z Position Sensitivity Surface events produce faster phonon pulses (test sample: nearest neighbor low-yield doubles (NNDs)) overall misidentification: < 2 x 10-6 for photons, < 2 x 10-3 for electrons Ionization Yield :1 scale: 3 in. x 1 cm, 1 mm separation Bulk electron recoils Surface electron recoils Nuclear recoils recoil energy 10!100 kev Bulk Electron Recoils Surface Electron Recoils 0.2 Accept as WIMP candidates Timing Parameter (µs) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 12

15 ZIP z Position Sensitivity Surface events produce faster phonon pulses (test sample: nearest neighbor low-yield doubles (NNDs)) overall misidentification: < 2 x 10-6 for photons, < 2 x 10-3 for electrons Ionization Yield :1 scale: 3 in. x 1 cm, 1 mm separation Bulk electron recoils Surface electron recoils Nuclear recoils recoil energy 10!100 kev Bulk Electron Recoils Surface Electron Recoils 0.2 Accept as WIMP candidates Timing Parameter (µs) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 12

16 ZIP z Position Sensitivity Surface events produce faster phonon pulses (test sample: nearest neighbor low-yield doubles (NNDs)) overall misidentification: < 2 x 10-6 for photons, < 2 x 10-3 for electrons Ionization Yield :1 scale: 3 in. x 1 cm, 1 mm separation Bulk electron recoils Surface electron recoils Nuclear recoils recoil energy 10!100 kev Bulk Electron Recoils Surface Electron Recoils 0.2 Accept as WIMP candidates Timing Parameter (µs) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 12

17 : CDMS II at Soudan Depth of 2000 meters water equivalent reduces neutron background to ~1 / kg / year Log10(Muon Flux) (/m 2 /s) 1 per minute in 4 m 2 shield Depth (mwe) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 13

The CDMS II Collaboration Brown University M. Attisha, R. Gaitskell, J.-P. Thompson Caltech Z. Ahmed, S. R. Golwala, D. Moore, R. W. Ogburn Case Western Reserve University D. S. Akerib, C. N.

18 The CDMS II Collaboration Brown University M. Attisha, R. Gaitskell, J.-P. Thompson Caltech Z. Ahmed, S. R. Golwala, D. Moore, R. W. Ogburn Case Western Reserve University D. S. Akerib, C. N. Bailey, K. Clark, M. Danowski, M.R. Dragowsky, D. R. Grant, R. Hennings-Yeomans Fermilab D. A. Bauer, M. B. Crisler, D. DeJongh, J. Hall, D. Holmgren, L. Hsu, E. Ramberg, J. Yoo MIT E. Figueroa-Feliciano, S. Hertel, S. Leman, K. McCarthy, P. Wikus NIST K. Irwin Queens University W. Rau Santa Clara University B. A. Young Syracuse University R.W. Schnee, M. Kos, J. M. Kiveni Texas A&M R. Mahapatra University of California, Berkeley M. Daal, J. Filippini, N. Mirabolfathi, B. Sadoulet, D. Seitz, B. Serfass, K. Sundqvist University of California, Santa Barbara R. Bunker, D. O. Caldwell, H. Nelson, J. Sander University of Colorado at Denver M. E. Huber University of Florida A. Achelashvili, T. Saab, D. Balakishiyeva, G. Sardane University of Minnesota P. Cushman, L. Duong, M. Fritts, V. Mandic, X. Qiu, A. Reisetter, O. Kamaev University of Zurich S. Arrenberg, T. Bruch, L. Baudis, M. Tarka Stanford University P.L. Brink, B. Cabrera, J. Cooley, M. Pyle, S. Yellin SLAC Summer Institute 2008/First CDMS II Five-Tower Results 14

19 CDMS Soudan Mine Installation Chicago MINOS cavern (neutrino beam from Fermilab) CDMS Huts, Fridge & Clean Rooms Soudan Low Background Counting Facility (uses Soudan II veto) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 15

20 CDMS Soudan Icebox and Shield Fridge Icebox Fridge C-stem Icebox Shield (lower portion) Icebox E-stem SLAC Summer Institute 2008/First CDMS II Five-Tower Results 16

21 CDMS Soudan Experimental Setup v. thick external polyethylene (41 cm) to stop H.E. neutrons (> 50 MeV) 23 cm thick lead sheild (incl. ancient lead, low in 210 Pb) Ancient lead µ-metal (with copper inside) 14 cm additional poly (neutron mirror effect) mu metal cryostat 41 cm Low Activity Lead Polyethylene SLAC Summer Institute 2008/First CDMS II Five-Tower Results 17

22 CDMS Soudan Experimental Setup SLAC Summer Institute 2008/First CDMS II Five-Tower Results 18

23 CDMS Soudan Experimental Setup SLAC Summer Institute 2008/First CDMS II Five-Tower Results 19

CDMS Soudan Runs Run* Start End Exposure (raw Ge) 118 10/11/03 1/11/04 53 kg-d 119 3/25/08 8/8/04 112 kg-d 123 10/21/06 3/21/07 430 kg-d Results Today 124 4/20/07 7/16/07 224 kg-d 125 7/21/07 1/09/08

24 CDMS Soudan Runs Run* Start End Exposure (raw Ge) /11/03 1/11/04 53 kg-d 119 3/25/08 8/8/ kg-d /21/06 3/21/ kg-d Results Today 124 4/20/07 7/16/ kg-d 125 7/21/07 1/09/ kg-d 20x calibration 70%livetime 126 1/17/08 ongoing 266 kg-d R118 and 119: 1 and 2 towers, resp. R123 onward: 5 towers This analysis: R123/124 = 4 x R118/119 In the can: 8 x R118/119 Expected by end 2008: 12 x R118/119 Photon cal data = 20x WIMP exposure 70% live: 15% dead due to DAQ and maintenance, 15% due to gamma cal cold since Oct 2006! *Soudan runs start at 100! (vs. Stanford runs) SLAC Summer Institute 2008/First CDMS II Five-Tower Results 20

WIMP Search Data Single-scatter nuclear recoils (regardless of phonon timing) remain blinded until all cuts set and initial leakage estimates made.

25 WIMP Search Data Single-scatter nuclear recoils (regardless of phonon timing) remain blinded until all cuts set and initial leakage estimates made. Due to time constraints, only Ge detectors have been analyzed; dominates WIMP sensitivity, fewer neutralization issues. SLAC Summer Institute 2008/First CDMS II Five-Tower Results 21

Opening the Box: Ionization Yield Cut Open the ionization yield box: we look at events that have correct yield to be WIMPs, but that have too fast phonon timing 97 singles in nuclear-recoil candidate

26 Opening the Box: Ionization Yield Cut Open the ionization yield box: we look at events that have correct yield to be WIMPs, but that have too fast phonon timing 97 singles in nuclear-recoil candidate region rejected by timing cut; these are surface events Consistent with leakage expected based on # of events between NR and ER bands and yield cut misid from photon cal # of multiple-scatter events seen in NR band. SLAC Summer Institute 2008/First CDMS II Five-Tower Results 22

27 The low-yield candidates that are accepted by the yield cut but rejected by timing cut are surface events. Estimated leakage of misidentified surface events determined from: Opening the Box: Phonon Timing Cut photon cal data WIMP-search multiples Cuts intentionally defined to obtain ~0.5 leakage events: optimal balance of efficiency and leakage Expect 0.6 +/- 0.5 misidentified surface events Expect < 0.2 unvetoed single-scatter neutrons SLAC Summer Institute 2008/First CDMS II Five-Tower Results 23

28 The low-yield candidates that are accepted by the yield cut but rejected by timing cut are surface events. Estimated leakage of misidentified surface events determined from: Opening the Box: Phonon Timing Cut photon cal data WIMP-search 0 Observed Events multiples Cuts intentionally defined to obtain ~0.5 leakage events: optimal balance of efficiency and leakage Expect 0.6 +/- 0.5 misidentified surface events Expect < 0.2 unvetoed single-scatter neutrons SLAC Summer Institute 2008/First CDMS II Five-Tower Results 23

Spin-Independent Exclusion Limit CDMS II target sensitivity CDMS II likely reach Zero events observed Including reanalysis of prior data set (Ogburn thesis (Stanford), PRD in prep), obtain best

29 Spin-Independent Exclusion Limit CDMS II target sensitivity CDMS II likely reach Zero events observed Including reanalysis of prior data set (Ogburn thesis (Stanford), PRD in prep), obtain best spin-independent limit for M > 40 GeV/c 2 ~ 2X exposure of current analysis waiting in hand. >3X by end Will surpass CDMS II target sensitivity of 2 x cm 2 Submitted to PRL; preprint available at cdms.berkeley.edu SLAC Summer Institute 2008/First CDMS II Five-Tower Results 24

30 where the coming generation is aiming, pb Many technologies under development promise pb, but the devil is in the details! 1 ev /1 kg /1 day Future of Direct Detection 1 ev /1 kg /100 days 1 ev/ 100 kg /100 days Cross-section [cm 2 ] (normalised to nucleon) Gaitskell,Mandic,Filippini Ambitious and exciting times! WIMP Mass [GeV/c 2 ] CDMS plans: 25 kg moving ahead (c.f. XENON100, LUX300, WArP140) Technology development aiming at 6 x 2 (5 kg!) detector demo in 2009 to make 100-kg (N=20) and ton-scale (N=200) CDMS feasible. SLAC Summer Institute 2008/First CDMS II Five-Tower Results 25 DAMA XENON KIMS CRESST EDELWEISS ZEPLIN II WARP CDMS Soudan 2008 CDMS Soudan Proj Projections: DEAP/CLEAN 25 kg XENON100 WArP 150 kg SuperCDMS SNOLab DEAP/CLEAN 150 kg LUX 300 kg XENON 1T DEAP/CLEAN 1T

31 where the coming generation is aiming, pb Many technologies under development promise pb, but the devil is in the details! 1 ev /1 kg /1 day Future of Direct Detection 1 ev /1 kg /100 days 1 ev/ 100 kg /100 days Cross-section [cm 2 ] (normalised to nucleon) LEP excluded Gaitskell,Mandic,Filippini Ambitious and exciting times! WIMP Mass [GeV/c 2 ] CDMS plans: 25 kg moving ahead (c.f. XENON100, LUX300, WArP140) Technology development aiming at 6 x 2 (5 kg!) detector demo in 2009 to make 100-kg (N=20) and ton-scale (N=200) CDMS feasible. SLAC Summer Institute 2008/First CDMS II Five-Tower Results 25 DAMA XENON LHC reach KIMS CRESST EDELWEISS ZEPLIN II WARP CDMS Soudan 2008 CDMS Soudan Proj ILC 500 reach Projections: DEAP/CLEAN 25 kg XENON100 WArP 150 kg SuperCDMS SNOLab DEAP/CLEAN 150 kg LUX 300 kg XENON 1T DEAP/CLEAN 1T

32 Ton-Scale Detector Development Increasing single-detector size is key SuperCDMS 25kg: detector thickness x2.5 to scale from 5 kg to 25 kg Current surface event rates sufficient to reach 1 x cm 2 with no improvements; only need to increase mass at no loss of rejection power Ton-scale CDMS: detector diameter to 6 to reach kg (surface contamination (nuclei/cm 2 ) x misid prob.) needs to be improved by (mass ratio) / (thickness ratio) Continuing analysis improvements historically provide this: have aimed for O(0.5 leakage) in each data set, with T1: 4 x cm 2, T1-5: 4.6 x cm 2 project ratio kg / det # det tot kg fiducial CDMS II x % SCDMS 25 kg x % R&D SCDMS 1000 kg x 10 x % 90% SLAC Summer Institute 2008/First CDMS II Five-Tower Results 26

33 Conclusion Significant new results from CDMS II five-tower data Another factor of >3 in sensitivity expected Backgrounds largely understood Moving ahead with 25 kg experiment Ton-scale R&D also beginning Very exciting time for SUSY WIMP searches with accelerating sensitivities of direct searches and imminent turn-on of LHC SLAC Summer Institute 2008/First CDMS II Five-Tower Results 27

CDMS-II to SuperCDMS

CDMS-II to SuperCDMS WIMP search at a zeptobarn Tobias Bruch University of Zürich 5 th Patras Workshop on Axions,WIMPs and WISPs University of Durham, 13 July 2009 CDMS-II 5 Tower setup 5 Towers a 6 detectors