Status of the Cryogenic Dark Matter Search (CDMS) Experiment Bruno Serfass University of California,...
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Transcript of Status of the Cryogenic Dark Matter Search (CDMS) Experiment Bruno Serfass University of California,...
Status of the Cryogenic Dark Matter Search
(CDMS) Experiment
Bruno SerfassUniversity of California, Berkeley
for the CDMS Collaboration
Rencontres de Moriond – March 2005
2
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 FloridaL. Baudis, S. Leclercq
University of Minnesota
J. Beaty, 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, 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
CDMS II: The People…
3
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
CDMS II Overview
4
Ionization Yield EQ/ER
Y~ 1 for electron recoils
Nuclear Recoils (252Cf)
Nuclear Recoils (252Cf)
WIMPS (and neutrons) scatter off nuclei
Identify nuclear recoils event by event!
Y~ 0.3 (Ge) for nuclear recoils
• Events occuring near the surface (<~10 m) have an incomplete charge collection (“dead layer”) and can be misidentified as nuclear recoils
Nuclear Recoils (252Cf)
Nuclear Recoils (252Cf)
• Surface events:
Electrons produced by radioactive beta decays from surface contamination
Electrons ejected from nearby material by high energy x-rays
Gammas interacting within ~10 m of the surface
Most background sources (electrons, photons) scatter off electrons
Measure simultaneously ionization and athermal phonons
CDMS II Overview
Bulk Electron Recoils (133Ba)
Bulk Electron Recoils (133Ba)
51 tungsten380 x 60 aluminum fins
Q inner
Q outer
A
B
D
C
Rbias
I bias
SQUID array Phonon D
Rfeedback
Vqbias
The ZIP Ionization & Phonon Detectors
Qouter
Qinner
zy
x
Measure ionization in low-field (~volts/cm) with segmented contacts to allow rejection of events near outer edge
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-m-thick strip of W connected to 8 superconducting Al collection fins
2 charge electrodes:
• “Inner” fiducial electrode• “Outer” guard ring
6
The ZIP Towers
Ge (Z3)
Si (Z4)
Ge (Z5)
Si (Z6)
Ge (Z1)
Ge (Z2)
4 K
0.6 K
0.06 K
0.02 K
FET cards
Tower 1:
• 4 Ge and 2 Si ZIPs
• Thoroughly understood at Stanford
• Beta background on bottom Si detector (Z6)
SQUID
5 Towers now installed! 30 detectors: 19 Ge (4.75 kg) and 11 Si (1.1 kg)
Tower 2: 2 Ge and 4 Si
Tower 3, 4: 4 Ge and 2 Si each
Tower 5: 5 Ge and 1 Si
Tower 1
And…
7
Detector response 4 phonon pulses 2 charge pulses (Qinner, Qouter)
Informations on phonons pulse shape (ex. risetime), delay between charge and phonon pulses
Phonon sensors provide measurement of xy position:
• Phonons propagate at 0.5 (1) cm/s 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
Cd109 + Al foil: 22 kev
Delay Plot
We can correct the phonon energy/timing position dependence
8
Z-Position Sensitivity Rejects Surface events
Energy deposited near the surface gives rise to slightly lower-frequency phonons
undergo less scattering and hence travel ballistically
Shorter risetime than bulk events
Bulk eventSurface event
Surface event:
Overall rejection of surface events appears >99%
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)
Neutrons
Gammas
9
CDMS II at Stanford and at Soudan Log
10(M
uon
Flu
x)
(m-2s
-1) Stanford Underground
Facility (SUF)
Depth (meters water equivalent)
500 Hz muons in 4 m2 shield
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 68:082002 (2003)
Soudan Mine1 per minute in 4 m2 shield
2003-2005 in Soudan Mine (Minnesota)
Depth 713 m (2090 mwe)
Reduce neutron background:
~1/kg/day to ~ 1/kg/year
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Shielding, Veto at Soudan
Layered shielding (reduce , , neutrons) 40 cm outer polyethylene
Removes neutrons from (,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
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
Lead Polyethylene
mu-metal (with copper inside)
Ancient lead
11
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
Gaps were cryogenic fills and calibration runs (133Ba, 252Cf)
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
Soon beginning: Run (120) Towers 1-5
30 detectors: 19 Ge (4.75 kg) and 11 Si (1.1 kg)
Run 118
Run 119
12
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
Phonons calibrated to charge
Good agreement with the simulations
Ionization energy in keVIonization energy in keV
Phonon energy in keVPhonon energy in keV
MCdata
13
Cuts and Efficiency for Nuclear Recoils
No veto hit (97%) nor bad noise pre-trigger (95%)
Ionization yield (< 95%)
Timing cuts (vary with energy from ~30% to 80%)
ionization threshold In fiducial volume (< 85%)
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
Z1 threshold at 20 keVZ2, Z3, Z5 thresholds at 10 keV
Run 118
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WIMPs search data with Ge detectors (Run118)
Yellow points from neutron calibration
Ch
arg
e Y
ield
Prior to timing cuts After timing cuts
Blue points from WIMP search data (Z2, Z3, Z5)
Recoil energy (keV) Recoil energy (keV)
Ch
arg
e Y
ield
Expected background: 0.7 ± 0.35 mis-identified surface electron recoils ~0.07 unvetoed neutrons
Event
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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!
DAMA
CDMS SUF
EDELWEISS
CDMS Soudan
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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• Soudan Tower 1-2 (R119) in 2004 Analysis well underway plan to announce results at April APS!
Expected Run119
• Soudan Towers 1-5 (R120) in 2005
5 towers installed (19 Ge and 11 Si detectors) Cryogenic, electronics, DAQ upgrades
Expected
Run120
What’s next for CDMS II?
DAMA
CDMS-II explores MSSMs in series of runs:
• 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
17
Toward a ton-scale experiment: SuperCDMS
Remove Muon-induced Neutron Background…
…. by moving further down
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
Stanford
Soudan
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
Sensitivity improve:• If no background: Linearly with M (detector mass) and T (exposure time)• If background that can be estimate independently: √MT
Increase mass, remove backgrounds
SuperCDMS: Scientific goals
19
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 ~10-46 cm2
Submitted Development Project proposals
20
Backup slides
21
Electrothermal Feedback
Voltage bias supplied Joule heating P = V2/R
Quasi particles heat up W T R P P T Stability
ElectroThermal Feedback
R
T
Rshunt
Ibias
W ETF-TES
SQUID Array Measure reduction in
Joule heating by change in current
I = V/R E = IV dt
Nuclear recoils in Ge ZIPNuclear recoils in Ge ZIP
Cou
nts/
(ke
V k
g da
y)
Recoil Energy (keV)
103
102
Expectations from simulation
Data
Nuclear recoils in Si ZIPNuclear recoils in Si ZIP
Expectations from simulation
Recoil Energy (keV)
104
103
102
Cou
nts/
(ke
V k
g da
y) Data
Phonon calibration does not depend on whether the event is a nuclear recoil or electron recoil
0
5
10
15
0
2
4
6
8
10-1
-0.5
0
0.5
1
X Position [mm]Z Position [mm]
Volta
ge [V
]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.
Double-sided phonon sensors
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Theory survey - earlier MSSM
Baltz & Gondolo PRD67 065503 (2003)Kim,Nihei,Roszkowski, hep-ph/0208069
Baltz & Gondolo hep-ph/0102147
25
Constrained MSSM and relax GUTs
Baer et al, hep-ph/0305191Chattopadhyay et. al, hep-ph/0407039Ellis et al, hep-ph/0306219
Bottino, et al hep-ph/0307303
26
mSUGRA and Split Supersymmetry
Baltz & Gondolo hep-ph/0407039 A. Pierce, hep-ph/0406144 &G. F. Giudice and A. Romaninohep-ph/0406088
27
NeutronProton
Spin dependent WIMP-nucleon Interactions
Preliminary