Status of the Cryogenic Dark Matter Search · TeVPA 8 Analysis Technique L o w y i e l d s i n g l...
Transcript of Status of the Cryogenic Dark Matter Search · TeVPA 8 Analysis Technique L o w y i e l d s i n g l...
Status of the CryogenicDark Matter Search
Lauren HsuFermilab
TeV Particle AstrophysicsJuly 13, 2009
TeVPA 2009 2
Is Dark Matter a WIMP?
M. Attisha
Kolb & Turner, “The Early Universse”
particles with mass and annihilation cross section at the weak scale naturally yield correct relic density of CDM
χχ
χ
χ-
q
q-
Look for nuclear recoil from WIMPscatter
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CDMS Experiment
CDMSII at Soudan:Five Towers (30 ZIPS)
operating since June ‘06
1 µ tungsten 380µ x 60µaluminum fins
Z-sensitiveIonization andPhonon detectors
Soudan Mine
Most sensitive to spin-independent scattering: σ∝ A2
4.75 kg Ge(A=73), 1.1 kg Si(A=28)
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Detection Strategydiscrimination and shielding maintain a <1 event background experiment
elec
tron re
coils
nuclear recoils
Ephonon
Ech
arge
4 phonon channels
(each is 1036Treansition EdgeSensors in parallel)
inner sensor+
outer guard
(phonon side)
(chargeside)
Signature of a Nuclear Recoil:reduced ionization signal relative to
phonon signal
Major Backgrounds:
• Gammas/Betas (electron recoils)
• Neutrons (nuclear recoils)• Surface Events
19 Ge zips (250 g each)
11 Si zips (100 g each)
1 cm thick crystals
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• 133Ba• 252Cf
Gamma Rejection
ionizationyield
Echarge
Ephonon
=
2σ electron recoil band
2 σ nuclear recoil band
BETTER THAN 1:104 rejection of gammas basedon ionization yield alone
elec
tron
rec
oils
nuclear recoils
Ephonon
Ech
arge
ancient lead shielding
ultra-clean materialsand careful handling
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Neutron Backgrounds
Soudan Mine: 2090 mwe
muon veto ~98% efficient
2 layers polyethylene -shields from cosmogenic and
radiogenic neutrons
(muon rate reduced by >104 ) << 1 unvetoedsingle scatter
neutron / kg /year
GEANT4
FLUKA+MCNPX
MUSIC
Neutrons maydouble scatter orbe accompanied by
EM shower
1. Go Deep: 2. Use Active Shielding:
3. Use Passive Shielding:
4. Use Event Topology
5. Run Extensive Simulations:
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Surface Events10 µm “dead layer” results in reducedionization collection
• 133Ba• 252Cf
These events are primarily electrons,gammas and x-rays originating fromsurfaces of the detectors andsurrounding materials
Phonon pulse shape (timing) distinguishes surface events
Both yield and “timing” rejects these events
approximatesignal region
surfaceevent
nuclearrecoil
rising edge slope
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Analysis Technique
Low yield singles masked
Candidate Criteria:• Data Qualty + Fiducial Volume Cut• Muon-veto anticoincident• Single Scatter (only 1 zip w/ signal)• Ionization yield within 2σ nuclear recoilband• Phonon “timing” cut - reject surfaceevents
All cuts established before unblinding!
Cut EfficienciesCDMSII 2008 result
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Our Current Limit
398 raw kg-d121 kg-d (for 60 GeV/c2 WIMP)
10 - 100 keV analysis range
Expected Surface Events:
PR
L 102, 011301 (2009)
(α,n): < 0.03(fission): < 0.1Cosmogenic: < 0.1 (MC 0.03-0.05)
Expected Neutrons:
ZERO Events Observedin Signal Region!
CDMS II 2008: 1st Five Tower Result
4.6x10-44cm2
@90% CL
10
coming soon…
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CDMS II 2009Projected Sensitivity
~2.5X moretotal
exposure
Ge Exposures:• CDMS II T1+T2 ~120 kg-d• CDMS II 2008 ~400 kg-d• CDMS II 2009 ~750 kg-d
Results expectedAugust ‘09
Baltz, Gandolo 2004Roszkowski et al. 2007, 95 % CLRoszkowski et al. 2007, 65% CLCDMS II T1+T2 Ge reanalysisZeplin III 2008XENON 10 2007CDMS II 2008 GeCDMS II 2008 Ge Combined
(after nominal quality cuts)
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Calibration Data Preview
• 133Ba• 252Cf
CDMS II 2008
Recoil Energy (keV)
Ioni
zatio
n Yi
eld
Initial studies indicate the data is very well behaved…even better than previously published data!
• 133Ba• 252Cf
CDMS II 2009
Recoil Energy (keV)
Ioni
zatio
n Yi
eld
tighter bands!
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Promising Surface EventRejection
Aiming for ~X2 better rejection of surface events to keep up with exposurepotential and stay a <1 background experiment
Note: Ba/Cf exposures are different between datasets andhasn’t been corrected for here
approximatesignal region
• 133Ba e-recoil
• 133Ba surface
• 252Cf n-recoil
Timing Parameter (µs)
Ioni
zatio
n Yi
eld
(shown for 1 zip)
Timing Parameter (µs)
- 2008 133Ba surface- 2008 252Cf neutron- 2009 133Ba surface- 2009 252Cf neutron
Surface EventDiscrimation
CDMS 2009 Calibration Data
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SuperCDMS
• modified Al fin layout, improves phononcollection efficiency
• cleaner, simplified, and streamlinedproduction
• “mercedes” phonon sensor layout, outerphonon “guard”
15 kg of Ge at Soudan, arranged as 5 SuperTowers
“mercedes” zip
SuperTower CDMSII Tower
• 2.5X thicker (1-inch)Ge crystals
• “endcap” Ge vetodetectors in each tower
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First SuperTower Installation
CDMS II data-takingended March 2009
First SuperTowerinstallation is now
complete!
Testing currentlyunderway
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SuperCDMS FutureCDMS II4 kg Ge
~ 2 yrs operation
SuperCDMS @ Soudan15 kg Ge
~ 2 yrs operation
SuperCDMS @ Snolab100 kg Ge
~ 3 yrs operation
DUSEL/GEODM1.5T
~LHCprojectedlimit
LHCbenchmarks
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summaryCDMS has a world-leading limit on the spin-independent WIMP
annihilation cross section:
4.6x10-44cm2 at 90% CL (for 60 GeV/c2 WIMP mass)
~750 kg-days of five-tower data is currently being analyzed.Results expected by end of summer
First SuperCDMS tower is installed and is nearly ready fordata-taking
Steady progress to zeptobarn cross sections and smaller!
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Thank You
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backup slides
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Other CDMS Results for2009
“Analysis of the low-energy electron-recoil spectrum ofthe CDMS experiment” - arXiv: 0907.1438 [astro-ph]
“Search for Axions with the CDMS Experiment”- arXiv:0902.4693 [hep-ex]
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Energy Resolution
Ionization Energy [keV] Phonon Energy [keV]
Ionization Energy [keV]
356 keV
Phonon Energy [keV]
356 keV
10.4 keV 10.4 keV
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Signal Region CDMSII 2008
PRL 102, 011301 (2009)
WithoutTiming Cut
WithTiming Cut
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What are Surface Events?
~10 μm“deadlayer”
-3V
carrier backdiffusion
Reduced charge yield due to chargecarrier back-diffusion in surface events.
Correlations to 210Pb contamination observed, most likely frombeta decays on surface of detectors
210Po taggedα-decays
210Pb taggedβ-decays
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What is Dark Matter?
Bullet Cluster
Rotational Curves WMAP 5-year
Strong Lensing