direct detection searches for dark mattercrunch.ikp.physik.tu-darmstadt.de/erice/2010/sec/... ·...
TRANSCRIPT
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Enectali Figueroa-FelicianoMassachusetts Institute of Technology
Direct Detection Searches for Dark Matter
International School of Nuclear Physics32nd Course: Particle and Nuclear Astrophysics
Erice
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Outline
• Overview of the Dark Matter Problem
• Principles of Direct Detection
• Experimental Searches for WIMPS
• The CDMS Experiment
• Outlook for the future
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The Concordance Model of Cosmology
We don’t know
what 96% of the
Universeis made
of!!! Dark EnergyDark MatterFree H & HeStars and GasNeutrinosHeavy Elements (Us)
Dark Energy72%
Dark Matter23%
Free H & He4%
0.03% All rocky planets and their inhabitants are found here
No Big Bang
1 2 0 1 2 3
expands forever
-1
0
1
2
3
2
3
closed
recollapses eventually
Supernovae
CMB
Clusters
open
flat
Knop et al. (2003)Spergel et al. (2003)Allen et al. (2002)
Supernova Cosmology Project
!
!"
M
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
• The Missing Mass Problem:
• Dynamics of stars, galaxies, and clusters
• Rotation curves, gas density, gravitational lensing
• Large Scale Structure formation
• Wealth of evidence for a particle solution
• MOND has problems with Bullet Cluster
• Microlensing (MACHOs) mostly ruled out
• Non-baryonic
• Height of acoustic peaks in the CMB (Ωb)
• Power spectrum of density fluctuations (Ωm)
• Primordial Nucleosynthesis
• And STILL HERE!
• Stable, neutral, non-relativistic
• Interacts via gravity and/or weak force
The Nature of Dark Matter
Clowe et al., ApJ, 648, 109
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
WIMPs and WISPs• We “know” that Dark Matter
• Has mass• Is non-baryonic• Was non-relativistic early on in
cosmological time• Has a certain annihilation cross
section• Should have a non-zero cross section
with quarks
• The Lightest Super Particle (LSP) in many Minimally Supersymmetric Standard Models is a viable candidate. These are called Weakly Interacting Massive Particles: WIMPs
(Roszkowski 2004)
• Another set of candidates are Weakly Interacting Sub-eV Particles: WISPs. This set includes axions and axion-like particles.
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Non-baryonic Menu• Axions
• Axino
• Gravitino
• Sterile Neutrinos
• WIMPs
• And many more exotics that can fit the bill...
Dark MattCafé
no, we don’tserve quark soup!
Talk by Frank Daniel Steffen
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Annihilation in the Cosmos
FERMI, Pamela, ATTIC
The Hunt for Dark MatterProduction in Colliders
Scattering in Terrestrial Detectors
LHC
CDMS
HESS, VERITAS, Magic
XENON100
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Annihilation in the Cosmos
FERMI, Pamela, ATTIC
The Hunt for Dark MatterProduction in Colliders
Scattering in Terrestrial Detectors
LHC
CDMS
HESS, VERITAS, Magic
XENON100
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Outline
• Overview of the Dark Matter Problem
• Principles of Direct Detection
• Experimental Searches for WIMPS
• The CDMS Experiment
• Outlook for the future
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Why WIMPs?• Supersymmetry (SUSY)
appears in many theories for physics beyond the standard model.
• R-parity guarantees that most SUSY theories have a stable LSP.
• From cosmology, the freezeout density requires an interaction cross section in the weak scale (the WIMP miracle)
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
• Energy spectrum & rate depend on WIMP distribution in Dark Matter Halo
• “Spherical-cow” assumptions: isothermal and spherical, with Maxwell-Boltzmann velocity distribution
• vo = 220 km/s, vrms = 270 km/s, vesc= 650 km/s
• ρ = 0.3 GeV / cm3
• Assume mass = 60 GeV/c2
• Density = 5000 part/m3
moo
Direct Detection and WIMP Astrophysics
10 WIMPs on average, inside a 2 liter bottle
(if mass=60 x proton)
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
The Dark Matter Wind
apparently “blows” from Cygnus
Our speed relative to the halo is ~220 km/s
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Flux
• Density: 0.3 GeV/cm3
• Mass: assume 60 GeV/c2
• @ ~220 km/s
• ~100,000 particles/cm2/sec
• About 20 million/hand/sec
Enectali Figueroa-Feliciano - Vanderbilt 2009
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Enormous enhancement for
heavy nuclei target!
• Spin-Independent:
• The scattering amplitudes from individual nucleons interfere.
• For zero momentum transfer collisions(extremely soft bumps) they add coherently:
Wimp-Nucleus Interaction
mr =mχmN
mχ + mN= “reduced mass”
coupling constant
σo �4m2
r
πfA2
atomic mass
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• Spin-Dependent:
• Dominated by unpaired nucleons.
• For spinless nuclides, SD cross section = 0.
• For zero momentum transfer collisions (extremely soft bumps) the cross section is approximately:
Wimp-Nucleus Interaction
nuclear spin
σo =32(J + 1)
πJG2
F m2r
�ap�Sp� + an�Sn�
�2
Fermi Constant
Linear with J; spin-independent is usually dominant
coupling constant
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InteractionRate
[counts/keV/kg/day]
local properties of DM halo
nuclearstructure
Principles of Direct Detection
mr =mχmN
mχ + mN“reduced mass”
vmin =�
ER mN/(2m2r) minimum WIMP velocity for given ER
“form factor” (quantum mechanics of interaction with nucleus)
F (ER) � exp�−ER mN R2
o/3�
integral over local WIMP velocity distribution T (ER) � exp(−v2
min/v2o)
particle theory
dR
dER=
σo
mχ
F 2(ER)m2
r
ρo T (ER)vo√
π
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
WIMP Hunting•Elastic scattering of a WIMP from a nucleus deposits a small, but detectable amount of energy ~ few x 10 keV
•Featureless exponential energy spectrum with 〈E〉 ~ 50 keV
•Expected rate < 0.01/kg-day (based on σχ-n and ρ)
•Radioactive background a million times higher
•Background Reduction/Rejection is key
Low background (< 1) almost a prerequisite for discovery
WIMP Differential Event Rate
GeSiXe
mχ = 100 GeV/c2
σχ-n = 10-45 cm2
0 50 10010-5
10-4
10-3
10-2
Recoil [keV]
Cou
nts/
keV/
kg/d
ay
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Signal and Backgrounds
Nucleus
Electron
χ0v/c ≈ 7×10-4 = 210 km/s
Er ≈ 10’s KeV
n,γ
v/c ≈ 0.3
α,β,
Background is millions of times
higher than desired signal!
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Phonons
Ionization
Scintillation
The energy from scattering events in the atom evolves through different channels
Energy Channels
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Discrimination Strategies
Nucleus
ElectronRatios (like
Ionization/Phonon) have discrimination
power!
χ0n,
More Phonons
γ
v/c ≈ 0.3
α,β,
More Ionization and/or Scintillation
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Phonons10 meV/ph
100% energy
Ionization~ 10 eV/e
20% energy
Scintillation~ 1 keV/γ
few % energy
CRESSTROSEBUD CDMS
EDELWEISS
ZEPLIN II, IIIXENON
LUXWArP ArDMSIGN
NAIADDAMA/LIBRA
ZEPLIN IDEAP
CLEANXMASS
CUORECRESST I
Ge, Si
Xe, Ar, Ne
TeO2, Al2O3, LiF
CaWO4, BGOZnWO4, Al2O3 ...
DRIFTDM-TPC
IGEXCOUPPCOSME
CoGeNTANAIS
Ge, CS2, C3F8
Discrimination Strategies
NaI, Xe, Ar, Ne
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Thinking outside the Triangle...
• Scintillation Timing (DEAP/CLEAN)
• Signal Modulation (DAMA/LIBRA, DRIFT, DM-TPC, etc...)
• Nuclear-recoil-only trigger mechanism (a la COUPP...)
• Self-Shielding (XMASS)
• Others...
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Backgrounds• Backgrounds are much higher
than the signal event rate
• e.g. rate of 40K from a person standing 2 m away from Ge detector is 104 x expected dark matter signal!
• Gamma-rays and beta decays:
• Shielding: low activity lead, clean copper, water, noble liquids (active), …
• Select gamma-clean materials
• Neutrons from fission and (alpha,n) interactions from U/Th decays
• Neutron moderator: polyethelyne, paraffin, water, …
• Neutrons from cosmic ray muons:
• Use muon veto, neutron veto, shielding
• Go deep underground to reduce muon flux!
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
How to Separate Signal from Background?
• Statistical signature of WIMPs• Requires significant sample of WIMP recoil
events.• Annual Modulation in the WIMP recoil
spectrum. Earth’s velocity through the galactic halo is max in June, min in December (DAMA/LIBRA).
• Daily modulation of the incident WIMP direction. Measure the direction of the short track produced by nuclear recoil. (DM-TPC)
• Event-by-event discrimination• Requires powerful particle identification
technique at low energies.• Allows to extract good sensitivity from relatively
small exposures.
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Outline
• Overview of the Dark Matter Problem
• Principles of Direct Detection
• Experimental Searches for WIMPS
• The CDMS Experiment
• Outlook for the future
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CDMS IIDUSELLUX/ LZ?
MAX?GEODM?
BoulbyNaIAD
ZEPLINDRIFT
EdelweissOrpheus
XMASSKIMS
CsI LiFElegant
Gran SassoDAMA/LIBRA
CRESSTGENIUSCUOREXENONWARP
COUPP
CanFrancIGEX
ROSEBUDANAIS
IGEX-DM
Dark Matter Map
SNOLABPicassoCOUPP
SuperCDMS?
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Looking for the needle in the haystack
γ
γ
γ γ
γγ
γ
γ
γγ
γ
γ
γ
γ
γ
γ
γ
γγ
γγχ0
β
β
βββ
β
ββ
β
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
DAMA / LIBRA
• Talk by Rita Bernabei
• Eur. Phys. J. C (2010) 67: 39–49
Modulation signal at the level of
0.0116 ± 0.0013) cpd/kg/keV
1.17 ton × yr13 anual cycles
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
DM-TPC
• A Directional Dark Matter Detector
• Seeks to see the Daily Modulation of the Dark Matter Signal due to the rotation of the Earth through the prevailing “Dark Matter Wind”
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zx
z
x00:00 h
12:00 h
The direction modulation
Cygnus
Declination of Cygnus ~42o
Spergel, PRD, 1988
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-V
GND
+V
E
Low pressure gas
CF4
50-75 torr
Drift
Amplify
Time Projection Chamber
Side view
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-V
GND
+V
ER
Eχ
χ
Drift
Amplify
Recoil (few mm long)
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-V
GND
+V
ER
Eχ
χ
Drift
Amplify
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-V
GND
+V
ER
Eχ
χ
Drift
Amplify
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-V
GND
+V
ER
χ
χCamera
Charge
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Cf-252 neutrons
Measurement of head-tail
Dujmic et al. Astropart. Phys. 30 (2008) arXiv:0804.4827100 pixels = 6 mm
6 mm
935 keV 550 keV
530 keV 475 keV
365 keV 313 keV
P = 75 torr
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
DM-TPC Status
• Installing a 10 liter CF4
detector underground at WIPP
• Expect competitive sensitivities to Spin-Dependent WIMPs.
COUPP (2010)
10L detector6 months @ WIPP
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
COUPP
• Superheated Bubble Chamber
• Insensitive to photons (but sensitive to alphas)
• Uses superheated CF3I (sensitive to both spin-dependent and spin-independent)
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
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Bubbles!
neutrton alpha
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Acoustic Discrimination Between Neturons and Alphas
Neutron Alpha Particle
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
COUPP Spin-Dependent Limit
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
COUPP 60 kg
• A 60 kg bubble chamber is being tested at Fermilab and will be moved to SNOLab in the near future...
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CoGeNT
• P-type Point Contact Germanium Detector
• 440 g detector
• Low 0.4 keVee threshold
• Operating in Soudan Mine in Minnesota
arXiv: 1002.4703v2
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Surface Event Discrimination
• Slower Risetime of pulses on the n+ surface allows a cut to be placed on DM search data (lower)
• Inset shows fast and slow risetime pulses
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
cosmogenics
7 GeV WIMP10 GeV WIMP
WIMP Signal?
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CoGeNT Signal Region
CDMS “signal from 2 events”
DAMA
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Interpretations...
• Hooper et. al give a possible WIMP candidate consistent with CoGeNT, DAMA, CRESST, and the null results by XENON and CDMS.
arXiv:1007.1005v2
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Should we uncork the Champagne?
• CDMS will report very soon on new Si low-threshold limits…
• Stay tuned…
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Liquid Noble Detectors• Time Projection Chambers (already covered)
• XENON (talk by Christian Weinheimer)
• LUX (a cousin of XENON)
• Zeplin (also a Xe TPC)
• WArP (uses Argon)
• Single Phase Detectors
• DEAP / CLEAN (Argon and Neon)
• XMASS (800 kg under construction!)
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
XMASS• 800 kg Liquid XENON
in Kamioka
• Self-Shielding gives a low-background region in the middle of the detector.
• 100 kg Fiducial Volume
• WIMP search early next year.
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Data Coming Soon!
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Cryogenic Solid State Detectors
• Array of Smaller Detectors
• Potential for extreme background discrimination
• Aim to operate in “zero” background mode
• Main Players: • CRESST (talk by Josef Jochum)• Edelweiss (pictured)• CDMS
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Outline
• Overview of the Dark Matter Problem
• Principles of Direct Detection
• Experimental Searches for WIMPS
• The CDMS Experiment
• Outlook for the future
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS: The Big Picture
• Shielding
• Passive (Mine Depth, Pb, Poly)
• Active (muon veto shield)
• Energy Measurement
• Phonon (True recoil energy)
• Charge (Reduced for Nuclear)
• Position measurement (x,y,z)
• From phonon pulse timing
Use discrimination and shielding to maintain a Nearly Background Free experiment with cryogenic semiconductor detectors
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Observation Strategy1. Suppress all
backgrounds (factor of millions)
2. Discriminate between remaining background and desired signal (make your detector as smart possible)
γ
γ
γ γ
γγ
γ
γ
γγ
γ
γ
γ
γ
γ
γ
γ
γγ
γγχ0
β
β
βββ
β
ββ
β
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1.Suppress all backgrounds
Observation Strategy
Depth (mwe)M
uon
Inte
nsity
(m
-2y-1
)Depth (mwe)
Muo
n In
tens
ity (
m-2y-1
)780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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1.Suppress all backgrounds
Observation Strategy
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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1.Suppress all backgrounds
Observation Strategy
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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1.Suppress all backgrounds
Observation Strategy
41cm41cm
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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1.Suppress all backgrounds
Observation Strategy
41cm
23cm41cm
23cm
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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1.Suppress all backgrounds
Observation Strategy
41cm
23cm41cm
23cm
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
![Page 66: Direct Detection Searches for Dark Mattercrunch.ikp.physik.tu-darmstadt.de/erice/2010/sec/... · Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010](https://reader036.vdocument.in/reader036/viewer/2022070710/5ec407c43728b22f015583c5/html5/thumbnails/66.jpg)
1.Suppress all backgrounds
Observation Strategy
41cm
23cm
14cm
41cm
23cm
14cm
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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1.Suppress all backgrounds
Observation Strategy
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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1.Suppress all backgrounds
Observation Strategy
3” (7.6 cm)
1 cm Ge: 250 gSi: 100 g
3” (7.6 cm)
1 cm Ge: 250 gSi: 100 g
780 m rock (2090 m water equiv.)
Active veto muon scintillator
Polyethylene neutron moderation
Lead shields gammas
Ancient Lead shields 210Pb betas
Polyethylene shields ancient lead
Radiopure Copper inner can
Radiopure Ge “target”
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Phonons
Ionization
Scintillation
1.Suppress all backgrounds
2.Discriminate between remaining background and desired signal
Observation Strategy
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS Detector Array
41cm23cm
14cm41cm23cm
14cm
30-40 mK base temperature stage holds an array of Towers
Each Tower holds up to 6 detectors
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS Detector Array
30-40 mK base temperature stage holds an array of Towers
Each Tower holds up to 6 detectors
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS Detector Array
30-40 mK base temperature stage holds an array of Towers
Each Tower holds up to 6 detectors
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS Detector Array
30-40 mK base temperature stage holds an array of Towers
Each Tower holds up to 6 detectors
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS Detector Array
30-40 mK base temperature stage holds an array of Towers
Each Tower holds up to 6 detectors
![Page 75: Direct Detection Searches for Dark Mattercrunch.ikp.physik.tu-darmstadt.de/erice/2010/sec/... · Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010](https://reader036.vdocument.in/reader036/viewer/2022070710/5ec407c43728b22f015583c5/html5/thumbnails/75.jpg)
Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS Detector Array
30-40 mK base temperature stage holds an array of Towers
Each Tower holds up to 6 detectors
![Page 76: Direct Detection Searches for Dark Mattercrunch.ikp.physik.tu-darmstadt.de/erice/2010/sec/... · Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010](https://reader036.vdocument.in/reader036/viewer/2022070710/5ec407c43728b22f015583c5/html5/thumbnails/76.jpg)
Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS Detector Array
!"#$%&$'()&*+*,$$$
-".$%&$+/(%0$
!"#$%&$'()&*+*,$$$
-".$%&$+/(%0$
30-40 mK base temperature stage holds an array of Towers
Each Tower holds up to 6 detectors
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3” (7.6 cm)
1 cm Ge: 250 gSi: 100 g
Phonon side: 4 quadrants of athermal phonon sensorsEnergy & Position (Timing)
Charge side: 2 concentric electrodes (Inner & Outer)Energy (& Veto)
Transition Edge Sensors (TES) Operated at ~40 mK for good phonon signal-to-noise
CDMS II Detectors
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-3V
0V
CDMS II Detectors
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-3V
0V
CDMS II Detectors
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h+
e-
-3V
0VHot charge carriers (3eV/pair)
Quasi-diffusive THz phonons
CDMS II Detectors
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h+
e-
-3V
0VHot charge carriers (3eV/pair)
Quasi-diffusive THz phonons
Ballistic low-frequency phonons→
CDMS II Detectors
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h+
e-
-3V
0VHot charge carriers (3eV/pair)
Quasi-diffusive THz phonons
Ballistic low-frequency phononsBallistic Neganov-Luke phonons
→
CDMS II Detectors
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Q innerQ outer
Sensor ASensor BSensor CSensor D
Phonon Side
Charge Side
CDMS II Detectors
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Excellent Energy and Position Resolution
A D
CB
Am241 :γ 14, 18, 20, 26, 60 kev
Cd109 + Al foil :γ 22 kev
Cd109 :γ 22 kevi.c. electr 63, 84 KeV
Detector Calibration at Berkeley
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Excellent Energy and Position Resolution
A D
CB
Am241 :γ 14, 18, 20, 26, 60 kev
Cd109 + Al foil :γ 22 kev
Cd109 :γ 22 kevi.c. electr 63, 84 KeV
Detector Calibration at Berkeley
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Excellent Primary (γ) Background Rejection
γ source: Electron Recoil
N source: Nuclear Recoil
>104 Rejection of γ
Radioactive source data defines the signal (NR) and background (ER)
Yield = Ionization/Phonon
Very effective Particle ID
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Excellent Primary (γ) Background Rejection
γ source: Electron Recoil
N source: Nuclear Recoil
>104 Rejection of γ
Radioactive source data defines the signal (NR) and background (ER)
Yield = Ionization/Phonon
Very effective Particle ID
What are these drooping-yield events?
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Excellent Primary (γ) Background Rejection
γ source: Electron Recoil
N source: Nuclear Recoil
>104 Rejection of γ
Radioactive source data defines the signal (NR) and background (ER)
Yield = Ionization/Phonon
Very effective Particle ID
What are these drooping-yield events?
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Surface Eventsβs and low-energy γs don’t penetrate the detector. These surface events can pollute the signal region and are the dominant background for CDMS.
Single scatter surface event rate ~0.4 / kg / day
ExperimentMonte Carlo
85 keV β63 keV β
22 keV β
88 keV γ22 keV γ
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Bulkinitial phonons diffuse (slow)
Surfaceinitial phonons becomeballistic at surface (fast)
Secondary Discrimination: Phonon Timing
Surface Bulk
Time (µs)
Surface β Rejection
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Secondary Discrimination: Phonon Timing
Surface Bulk
Time (µs)
Surface β Rejection
Phonon Delay
Phon
on R
isin
g Sl
ope
Surfac
eBulk
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Secondary Discrimination: Phonon Timing
Surface Bulk
Time (µs)
Surface β Rejection
Phonon Delay
Phon
on R
isin
g Sl
ope
Surfac
eBulk
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Secondary Discrimination: Phonon Timing
Surface Bulk
Time (µs)
Surface β Rejection
timing parameter(delay & rising slope)
Bulk252Cf Neutrons
Surface133Ba
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Secondary Discrimination: Phonon Timing
Surface Bulk
Time (µs)
Surface β Rejection
timing parameter(delay & rising slope)
Bulk252Cf Neutrons
Surface133Ba
SignalRegion
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Setting the Signal Region
Calibration Neutrons
CalibrationGammas
SurfaceBetas
Signal Region
~15σ Away from Signal Band
Plus, vetos:not muonnot outer charge ringnot multiple detector
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Neu
tron
Eve
nt E
ffici
ency
Energy (keV)
Average Signal Efficiency: 0.32
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
CDMS II (2006-2008)30 detectors (5 Towers) installed in Soudan icebox: 4.4 kg Ge, 1.1 kg Si
Combination of Ge and Si Detectors•Neutron background measurement•WIMP Mass Measurement•Ge more sensitive to higher mass WIMPs, Si to lower mass WIMPs
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raw exposure
Total raw exposure is 612 kg-days
this work
2008 result
some detectors not analyzed for WIMP scatters
periods of poor data quality removed
612 kg-days raw
194 kg-days after signal region cuts
4 runs separated by partial warmups of cryostatDates of data taking: 7/2007 - 9/2008
recorded data
Data taken from 9/08-3/09: primarily an
engineering run
WIMP Search Exposure
2010 result
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Background Estimate
Surface Events: Data (we chose this)
Cosmogenic Neutrons: 0.04 ( )+0.04- 0.03
unvetoedvetoed
Monte Carlo
vetoed x
Data
Radiogenic Neutrons: 0.057 Materials Testing
MonteCarlo
&+0.0035- 0.02
0.6±0.1
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Opening the Box
BLINDED:
Recoil Energy (keV)
True
Ioni
zatio
n Yi
eld
Nor
mal
ized
Ioni
zatio
n Yi
eld
(σ)
Normalized Timing Parameter (µs)
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FAIL TIMING CUT:
Opening the Box
Recoil Energy (keV)
True
Ioni
zatio
n Yi
eld
Nor
mal
ized
Ioni
zatio
n Yi
eld
(σ)
Normalized Timing Parameter (µs)150 events in the NR band fail the ?ming cut, consistency checks deemed ok
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Opening the Box
PASS TIMING CUT:
Recoil Energy (keV)
True
Ioni
zatio
n Yi
eld
Nor
mal
ized
Ioni
zatio
n Yi
eld
(σ)
Normalized Timing Parameter (µs)
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Two Events!Opening the Box
Recoil Energy (keV)
True
Ioni
zatio
n Yi
eld
Nor
mal
ized
Ioni
zatio
n Yi
eld
(σ)
Normalized Timing Parameter (µs)
Candidate 1Tower 1, det 5 (T1Z5)Oct 27, 2007
Candidate 2Tower 3, det 4 (T3Z4)Aug 5, 2007
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Post-Unblinding Analysis
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What can we saypost-unblinding?
Candidate 1Oct 27, 2007
Candidate 2Aug 5, 2007
Tower 1, det 5
Tower 3, det 4
What can we saypost-unblinding?
Post-Unblinding Analysis
•separated by several months
•two different detectors
•both inner detectors (surface leakage uncertainties low)
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What can we saypost-unblinding?
Post-Unblinding Analysis
check everything:
muon veto performance goodcharge trapping rates normalKS tests of distributions goodnoise levels normalpre-pulse baselines normalelectron recoil rates normalsurface event rates normalradial position well-containedsingle-scatter identification goodspecial running conditions nooperator recorded issues no
Candidate 1Oct 27, 2007
Candidate 2Aug 5, 2007
Tower 1, det 5
Tower 3, det 4
What can we saypost-unblinding?
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Adjusted Background Estimate
Surface Events: Data (we chose this)
Cosmogenic Neutrons: 0.04 ( )+0.04- 0.03
unvetoedvetoed
Monte Carlo
vetoed x
Data
Radiogenic Neutrons: 0.057 Materials Testing
MonteCarlo
&+0.0035- 0.02
0.6±0.1
Unnoticed systematic atlow energies.
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Adjusted Background Estimate
Surface Events: Data (we ended with this)
Cosmogenic Neutrons: 0.04 ( )+0.04- 0.03
unvetoedvetoed
Monte Carlo
vetoed x
Data
Radiogenic Neutrons: 0.057 Materials Testing
MonteCarlo
&
0.82 (stat) (syst)+0.12- 0.10
+0.20- 0.19
+0.0035- 0.02
Probability of 2 or more leakage events : ~23%
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2010 Resultat 70 GeV: 3.8 x 10-44 cm2
Mass (GeV/c2)
WIM
P-N
ucle
on σ
SI (
cm2 )
2008 Resultat 70 GeV: 7.0 x 10-44 cm2
New σSI Upper Limit
DOI: 10.1126/science.1186112
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SuperCDMS phases - Moore’s Law if zero bkgd
4 kg
15 kg
150 kg
See e.g. ‘Background Penalty Factor’, Scott Dodelson arXiv 0812.0787v2
CDMSII Dec 2009
GEODM
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Enectali Figueroa-Feliciano - International School of Nuclear Physics, Erice 2010
Outline
• Overview of the Dark Matter Problem
• Principles of Direct Detection
• Experimental Searches for WIMPS
• The CDMS Experiment
• Outlook for the future
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• Next few years will have several experiments probing significant new parameter space.
• Look for new results from Liquid Nobels, Bubble Chambers, Scintillators, and Cryogenic Detectors.
The Future
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• We need several targets to check potential signal’s dependence on A and spin.
• We need several technologies with different systematics for cross checks and insurance against unexpected backgrounds in any one experiment.
The FutureExciting Times Ahead!