Prsentation PowerPoint

1
Status of the Cryogenic Dark Matter
Search (CDMS) Experiment
Bruno Serfass University of California,
Berkeley for the CDMS Collaboration
Rencontres de Moriond March 2005
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CDMS II The People
Brown University M.J. Attisha, R.J. Gaitskell,
J-P. F. Thompson Case Western Reserve
University D.S. Akerib, M.R. Dragowsky,
D.D.Driscoll, S.Kamat, A.G. Manalaysay, T.A.
Perera, R.W.Schnee, G.Wang University of
Colorado at Denver M. E. Huber Fermi National
Accelerator Laboratory D.A. Bauer, R. Choate,
M.B. Crisler, R. Dixon, M. Haldeman, D.
Holmgren, B. Johnson, W.Johnson, M. Kozlovsky,
D. Kubik, L. Kula, B. Lambin, B. Merkel, S.
Morrison, S. Orr, E.Ramberg, R.L. Schmitt, J.
Williams Lawrence Berkeley National
Laboratory J.H Emes, R. McDonald, R.R. Ross, A.
Smith Santa Clara University B.A. Young
Stanford University P.L. Brink, B. Cabrera, J.P.
Castle, C.L. Chang, M. Kurylowicz, L. Novak, R.
W. Ogburn, T. Saab, A. Tomada University of
California, Berkeley J. Alvaro-Dean, M.S. Armel,
M. Daal, J. Filippini, A. Lu, V. Mandic,
P.Meunier, N. Mirabolfathi, M.C.Perillo Isaac, W.
Rau, B. Sadoulet, D.N.Seitz, B. Serfass, G.
Smith, A. Spadafora, K. Sundqvist University of
California, Santa Barbara R. Bunker, D.O.
Caldwell, D. Callahan, R.Ferril, D. Hale, S.
Kyre, R. Mahapatra, J.May, H. Nelson, R. Nelson,
J. Sander, C.Savage, S.Yellin University of
Florida L. Baudis, S. Leclercq University of
Minnesota J. Beaty, P. Cushman, L. Duong, A.
Reisetter
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CDMS II Overview

• Cryogenic Dark Matter Search (CDMS) Experiment
  designed to search for Dark
• Matter in the form of WIMPs
• Detect them via elastic scattering on nuclei
  (nuclear recoils). Dominant
• backgrounds are electromagnetic in origin
  (electron recoils)
• WIMPs Extremely small scattering rate
  (fraction of 1 evt/kg/day), small energy
• of the recoiling nucleus (falling
  exponentially with ?E? 15 keV)
• Distinguish electron recoils (gammas, betas)
  from nuclear recoils (neutrons,
• WIMPs) event by event using Ge (Si) based
  detectors with two- fold
• interaction signature
• Ionization signal
• Athermal phonon signal
• Suppress neutron background by
• Going deep underground
• ?
  Soudan mine 713m below the surface
• Active muon veto, polyethylene shielding
• Relative event rates Singles vs multiples,
  Ge vs Si

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CDMS II Overview
Measure simultaneously ionization and athermal
phonons

• Most background sources (electrons, photons)
• scatter off electrons

Bulk Electron Recoils (133Ba)
Bulk Electron Recoils (133Ba)
Ionization Yield ? EQ/ER
Y 1 for electron recoils
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The ZIP Ionization Phonon Detectors

• 250 g Ge or 100 g Si crystal
• 1 cm thick x 7.5 cm diameter
• Photolithographic patterning
• Phonon sensors
• 4 quadrants with each 888 sensors (TES)
• operated in parallel
• TES 1-mm-thick strip of W connected to 8
• superconducting Al collection fins

Qouter
Qinner

• Measure ionization in low-field
• (volts/cm) with segmented contacts
• to allow rejection of events near outer edge

• 2 charge electrodes
• Inner fiducial electrode
• Outer guard ring

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The ZIP Towers
FET cards
SQUID
Tower 1
4 K 0.6 K 0.06 K 0.02 K

• Tower 1
• 4 Ge and 2 Si ZIPs
• Thoroughly understood at Stanford
• Beta background on bottom Si
• detector (Z6)

And

• Tower 2 2 Ge and 4 Si
• Tower 3, 4 4 Ge and 2 Si each
• Tower 5 5 Ge and 1 Si

5 Towers now installed! ? 30 detectors 19
Ge (4.75 kg) and 11 Si (1.1 kg)
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Detector response

• 4 phonon pulses
• 2 charge pulses (Qinner, Qouter)
• Informations on phonons pulse shape
• (ex. risetime), delay between charge
• and phonon pulses

Delay Plot

• Phonon sensors provide measurement
• of xy position
• Phonons propagate at 0.5 (1) cm/ms in Ge (Si)
• crystal ? measurable delays between
• the pulses of the 4 phonon channels
• Able to measure x,y coordinates of interaction
• Demonstrate by shining sources through a
• collimator

We can correct the phonon energy/timing
position dependence
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Z-Position Sensitivity Rejects Surface events
Surface event

• Energy deposited near the surface gives
• rise to slightly lower-frequency phonons
• ? undergo less scattering and hence
• travel ballistically
• ? Shorter risetime than bulk events

Neutrons
Gammas
Bulk event Surface event

• Overall rejection of surface events
• appears gt99
• We are only beginning to take full
• advantage of the information from the
• athermal phonon sensors!
• Improving modeling of phonon physics
• Extracting better discrimination parameters
• (timing and energy partition)

9
CDMS II at Stanford and at Soudan

• 2001-2002 run at Stanford (17 mwe of rock)
• 28 kg-day exposure of 4x 250g Ge detectors
• (and 2x 100g Si detectors)
• 20 nuclear-recoil candidates consistent
• with expected neutron background
• PRD 68082002 (2003)

Stanford Underground Facility (SUF)
500 Hz muons in 4 m2 shield
Log10(Muon Flux) (m-2s-1)
Depth (meters water equivalent)
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Shielding, Veto at Soudan
mu-metal (with copper inside)
Ancient lead

• Layered shielding (reduce g, b, neutrons)
• 40 cm outer polyethylene
• Removes neutrons from (a,n)
• 22.5 cm Pb, inner 5 cm is ancient
• 10 cm inner polyethylene
• Removes neutrons from muons
• 0.5 cm Copper walls of cold volume

Lead
Polyethylene

• Active Muon Veto
• Hermetic, 2 thick plastic scintillator
• veto wrapped around shield
• Reject residual cosmic-ray induced
• events
• Veto rate 600Hz
• One muon per minute is incident
• on the veto

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Summary of data taking at Soudan

• Oct. 2003 - Jan. 2004 Run (118) of Tower 1
• 4 Ge (1 kg) and 2 Si (0.2 kg) ZIPs (same tower as
  run 21 at Stanford)
• 53 live-days after in 92 calendar days
• ? Efficiency nearly
• 85 for last six weeks

Run 118

• Mar. 2004 Aug. 2004 Run (119) Towers 1,2
• 12 detectors 6 Ge (1.5 kg) and 6 Si (0.6 kg)
• 70 live-days after in 137 calendar days

Run 119

• Soon beginning Run (120) Towers 1-5
• 30 detectors 19 Ge (4.75 kg) and 11 Si (1.1 kg)

Gaps were cryogenic fills and
calibration runs (133Ba, 252Cf)
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Run 118 (Tower 1) Energy calibration with 133Ba
source

• Use 356 keV 133Ba lines to calibrate Ionization
• 10.4 keV (Ge activation), 303 keV, and 384 keV
  lines confirm linearity
• Calibrate Si using Monte Carlo

MC data
Ionization energy in keV
Phonon energy in keV

• Phonons calibrated to charge
• Good agreement with the simulations

13
Cuts and Efficiency for Nuclear Recoils

• Data cuts and threshold based on in situ gamma
  and
• neutron calibration
• Blind analysis The WIMP-search data were in
  sealed box (in
• particular nuclear-recoil region) until cuts
  finalized

Run 118
No veto hit (97) nor bad noise pre-trigger (95)
In fiducial volume (lt 85)
Ionization yield (lt 95)
Timing cuts (vary with energy from 30 to 80)
Z1 threshold at 20 keV Z2, Z3, Z5 thresholds at
10 keV
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WIMPs search data with Ge detectors (Run118)

• Blue points from WIMP
• search data (Z2, Z3, Z5)

Prior to timing cuts
After timing cuts
Charge Yield
Charge Yield

• Expected background
• 0.7 0.35 mis-identified surface electron
  recoils
• 0.07 unvetoed neutrons

Recoil energy (keV)
Recoil energy (keV)
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CDMS limit from Soudan

• Exposure after cuts of 52.6 kg-d raw exposure
  with Ge 20 kg-days for recoil energies between
  10-100 keV
• No nuclear-recoil candidates (1
  candidate with non-blind analysis)
• Expect 0.7 mis-identified surface electron
  recoils, 0.07 unvetoed neutrons (1.0 muon
  coincident neutron)
• New limit 10x (x4) better than CDMS SUF
  (EDELWEISS) at a WIMP mass of 60 GeV/c2
• Hard to accommodate DAMA annual modulation effect
  as a WIMP signal!

Minimum of the limit curve 4 x10-43 cm2 at 90
C.L for a WIMP mass of 60 GeV/c2
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Whats next for CDMS II?
CDMS-II explores MSSMs in series of runs
DAMA

• SUF Tower 1 in 2002
• Soudan Tower 1 (R118) in 2003/04
• PRL 93, 211201 (2004)
• More details PRD submission
• in March

Current CDMS limit
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Toward a ton-scale experiment SuperCDMS

• Sensitivity improve
• If no background Linearly with M (detector
  mass) and T (exposure time)
• If background that can be estimate
  independently ? vMT

Increase mass, remove backgrounds
Stanford

• Remove Muon-induced Neutron Background
• . by moving further down

Soudan

• At Stanford 17 mwe, 0.5 n/d/kg
• At Soudan 2090 mwe, 0.5 n/y/kg
• At SNOLab 6060 mwe, 1 n/y/ton

Sudbury (Canada)
Worry about neutrons from residual radioactivity
only

• Reduce photon and electron backgrounds
• Improve analysis, phonon-timing cuts
• Reduce raw rates via better shielding,
  cleanliness
• Improve detectors Increase detector thickness,
  double-sided phonon sensors,
• interleaved ionization electrodes

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SuperCDMS Scientific goals
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Conclusion

• The CDMS II experiment at the Soudan mine is
  at the forefront of the field.
• 2 runs are completed
• Run of Tower 1 (53 livedays with 4 Ge and 2 Si
  detectors)
• Results incompatible with DAMA for standard
  halo and WIMPS, PRL 93, 211201 (2004)
• Run of Towers 1 and 2 (70 livedays with 6 Ge
  and 6 Si detectors)
• Analysis well underway, results to be
  announced in April 2005
• 5 towers now installed (19 Ge and 11 Si
  detectors)
• Development project toward a ton scale
  SuperCDMS
• Zero-background goal
• Sensitivity to study WIMP physics down to
  s10-46 cm2
• Submitted Development Project proposals

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Backup slides
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Electrothermal Feedback

• Voltage bias supplied Joule heating P V2/R
• Quasi particles heat up W
• T? ? R ? ? P ?
• P ? ? T ? Stability

• Measure reduction in Joule heating by change in
  current
• I V/R
• E ? I?V dt

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Phonon calibration does not depend on whether the
event is a nuclear recoil or electron recoil
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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 lt 1.0 mm of the
  surface.

Double-sided phonon sensors
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Theory survey - earlier MSSM
Baltz Gondolo PRD67 065503 (2003) Kim,Nihei,Rosz
kowski, hep-ph/0208069
Baltz Gondolo hep-ph/0102147
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Constrained MSSM 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
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mSUGRA and Split Supersymmetry
A. Pierce, hep-ph/0406144 G. F. Giudice and A.
Romanino hep-ph/0406088
Baltz Gondolo hep-ph/0407039
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Spin dependent WIMP-nucleon Interactions
Preliminary
Proton
Neutron