searches for dark matter (the quest)
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Searches for Dark Matter (the Quest). Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003. Recap - Direct Detection. How to dredge the small (0.01 DRU= ev/(kg d keV)) up out of a bigger background (1 DRU typical) of recoil electrons from comptons?. - PowerPoint PPT PresentationTRANSCRIPT
Searches for Dark Matter(the Quest)
Harry Nelson
UCSB
2003 SLAC Summer Insitute
Aug. 5-6 2003
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Recap - Direct Detection
• Shield (shield radioactive too!)… 1 ev/(kg d keV) typical • Reduce the background… HDMS , IGEX , Genius • Exploit astron. propert. (year cycle, directionality) DAMA, DRIFT • Devise detectors that can distinguish nuclear recoil from electron recoil… Edelweiss, CDMS, Xenon..
How to dredge the small (0.01 DRU= ev/(kg d keV)) up out of a bigger background (1 DRU typical) of recoil electrons from comptons?
Indirect Detection(milli-) Charged Massive ParticlesClosing
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vDM1/2 300 km/s2
vDM1/2 =0 km/s2
Annual Modulation in Rate• `Usual Simplification’: Halo particles are at rest, on average• Sun moves through Halo - `apparent’ wind• Earth modulates `wind’ velocity yearly
vk = 15 km/s
Peak-to-peak up to 40%DAMA at Gran Sasso
Fig. from DRIFT
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Daily Modulation in Direction• Recoiling Nucleus Follows the Initial WIMP Direction… the `wind’
• Detector gaseous to reconstruct recoil direction• DRIFT at Boulby (Spooner)
Fig. from DRIFT
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DAMA – 100 kg of NaI
Iodine, A=127Eobs(KeVee)0.09 Erecoil (KeV)
Sodium, A=23Eobs(KeVee)0.25 Erecoil (KeV)
Erecoil Light
NaI
PM
T
PM
T
CopperLead
Poly
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through 2000 … 4
DAMA Background and Signal
through 2003 … 6.3
Bernabei et al., astro-ph/0307403
Energy Spectrum
Bkgd 1 cpd/kg/keV
2-6 KeV
8-24 KeV Na(23) 20-70 KeV I(127)
0.01950.031 -0.00010.019 cpd/kg/keV
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DAMA noise...
>1 pe threshold<10-4 cpd...
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DAMA Allowed Regions
through 2003through 2000(standard halo)
10-42
10-44
p (cm2), =0 /
• Variation mainly due to changes in halo parameters• two plots not directly comparable (different halos used)• With new result, DAMA ceases to employ `standard Maxwellian halo’ - comparisons challenging
Na
I
3
4
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Halo Variation
Kamionkowski and Kinkhabwala (1997)
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Perhaps WIMP couples not to nucleons, but to their spin S,V,T,A,P S,A non-relativistic (V too)
S - `nucleon, SI’ (or V) … A - `spin or SD’(also, could break isospin… np)A2 2 J(J+1)
DAMA
J0 unpaired nucleon, odd A
NAIAD (Boulby)(couple to proton spin)
10-36
10-34
p (cm2)Couple to neutron spin
LIBRA 250kg, NAIAD continues, ANAIS in Spain...
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0
v/c 710-4
NucleusRecoils
Dense Energy Depositionv/c small; Bragg
Discrimination of RecoilsSignal
Er
v/c 0.3
ElectronRecoils
Background
Sparse Energy Deposition
Er
Differences the Basis of Discrimination
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Simulation (by DRIFT)
40 keV Ar in 1/20 atm Ar 13 keV e- in 1/20 atm Ar
5 cm
Ar pushes other Ar atoms,none go very far.
Electron pushes otherelectrons, all go far
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dE/dx for different recoils http://www.srim.org/SRIM/SRIM2003.htm
Strategies
Detector insensitiveto small dE/dx(track etch, SDD)
Convert E to two distinct measured quantities that look different depending on whether nuclear recoil or electron.
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Track Etch Detectors
Mica,CR39
StruckNucleus
Large dE/dx
100 Å
Corrosive Etch
http://moedal.web.cern.ch/moedal/moedal_track.htm
Ancient Mica0.5109 yrExposure
fraction mm2
area
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Mica Result
58% 16O16% 28Si12% 27Al5% 39K
p (cm2) 10-37cm2
SD: 10-33cm2
Snoden-Ifft, Freeman, Price (1994)
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Superheated Droplet Detector (SDD)
10 m
Gelatin
Target, C2ClF5 (Liquid): Temp. > Boiling
0
Spin Dependent
15 gm
Collar et al., (2000)
10-36 cm2
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Lose the Gelatin… get all Target
Really a bubble chamber...CF3Br
Juan Collar and
Andrew Sonnenschein(poster session)
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NaI
Distinct Quantities to Measure
t
Gerbier et al., 1998
0.00001
0.0001
0.001
0.01
0.1
1
1 10 100
pulse time constant ns
0.00001
0.0001
0.001
0.01
0.1
1
1 10 100
pulse time constant (ns)
10-20keVLiquid XenonAlso a scintillator
(Spooner)
e- recoils from ’s
Nuclear recoils From neutrons
t (ns)1 10 100
’s
(50-100 keV ER)
Width of pulse
DAMA doesnot use this
NaI
ER: 130-150 KeV (I)
1) Time Structure of the Pulse2) Pulse Height/Area via:
a) Ionization (like Ge)b) Scintillation (like NaI)c) Heat/Phononsd) Physical Size of Ionization
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to electronsto electrons
Distinguishing Nuclear Recoil Nuclear recoil energy lost
mainly to collisions with other nuclei Nuclear recoils deposit lots of
energy in lattice excitations: phonons... heat
Nuclear motion poor at causing electronic excitation, ionization
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Simultaneous Measurement of Phonons(Heat) + Ionization
Temperature-20 mK Temp)/(Energy)
Temp)NTD Ge Slow (10’s ms)
Ionization - E applied
E
Background (e- from ) … strong ionization signal… equal phonon signal (!)
Nuclear recoil… reduced (by 1/4) ionization signal, strong phonon signal
Edelweiss
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Separation of Nuclear Recoil from e- Recoil
Shutt et al., 1992
Nuclear recoils (induced by a neutron source)
Electron recoils (induced by a source)
Slope really 1!
IonizationPhonons
=1 (bkgd)1/3 (sig)
Egap = 3/4 eVw = 3 eV
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Edelweiss (depth: 4500 mwe)
0.32 kg/ Ge detector
3×0.32kg GermaniumDetectors
Roman Lead
L. Chabert,EPS `03 Aachen
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Edelweiss Data: ’s Suppressed by 1000
● 7.51 kg.d exposure(fiducial volume)● Best charg. channel : 1 keV (FWHM)● 20 keV threshold
● 3.72 kg.d (fiduc.)● Smaller exposure due to electronics problems● 30 keV threshold
● 10.86 kg.d (fiducial)● Good phonon channel300 eV (FWHM) resolution during most of the runs● Noisy charge channel● 30 keV threshold
Bolometer 1 Bolometer 2 Bolometer 3
L. Chabert,EPS `03 Aachen
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Betas...
GermaniumElectrodeImplants
E
External Ionization electrons get trapped in this electrode
Those electrons never drift over to the other electrode… ionization signal reduced… but, all the phonons/heat still present… (ionization)/(phonons) < 1
z
CDMS effort: measure z
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Edelweiss and other’s results
CDMS no background subtraction hep-ex/030600128 kg-days (Ge, phonon/ion.)CDMS with background subtraction hep-ex/030600128 kg-days (Ge, phonon/ion.)
ZEPLIN I (preliminary)230 kg-days (Liq Xe)
EDELWEISS 2003no background subtraction31 kg-days (Ge, phonon/ion.)
L. Chabert,EPS `03 Aachen
DAMA/Edelweiss inconsistent at 99.9%...
... not accounting for differential systematics
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CDMS: not as deep… neutron background
17 mwe
Detectors Inner Pb shieldPolyethylene
Pb Shield
Active Muon Veto
Fridge
Copper
nn
n
R. Schnee... Experiment moved to
Soudan, 2100 mwe depth
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CDMS Layout, Data
ZIP 1 (Ge)ZIP 2 (Ge)ZIP 3 (Ge)ZIP 4 (Si)ZIP 5 (Ge)ZIP 6 (Si)
SQUID cards
FET cards
4 K0.6 K0.06 K0.02 K
4 Germanium Detectors (0.66 kg total) 2 Silicon Detectors (0.2 kg total) Small DM rate, high neutron rate
Nuclear Recoils
Surface electrons Z1 () or Z5 (+)
1/5000 ’s misid’ed as nuclear recoils
R. Schnee
8 cm
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Technology of `ZIP’s (Z for z)
Al
quasiparticle trap
Al Collector W Transition-Edge Sensor (TES)
Si or Ge
quasiparticlediffusion
phonons
Very different from Edelweiss, although the objective is the same… the `phono-cathode’
Cooper Pair
superconducting
normal
T (mK)Tc ~ 80mK
RTES
()
4
3
2
1
~ 10mK
• Signal much faster - microseconds
• 3-d imaging (Z)
R. Schnee
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The ZIP Phono`cathode’...
1 tungsten 380 x 60 aluminum fins
• 4 segments + timing to get x,y on the face• rise time to get z, into the face
R. Schnee
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ZIP Surface Electron Rejection
Neutrons from 252Cf source
(Single-scatter)
photons from60Co Source
Surface-electron recoils (selected via nearest-neighbor multiple scatters from 60Co source)
Accept
Reject
Surface electrons still likely to be the limiting background
R. Schnee
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CDMS Expected Background Levels
CDMS-II Proposal
0.0024
In DRU, ev/kg/kev/day
a bit dated; nowX10 better, surfaceelectron X2 better
0.000140.0005
0.00074
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Catalog of Recoil Experiments
Rick Gaitskell
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Future Performances R
ick
Gait
skell
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Prognostication
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A Proposal… 5 billion years ago…(indirect DM detection)
Get 1057 protons in a sphere (ignite to enable a neutrino program)Wait for WIMPs to collect (spin-dependent cross section - proton’s spin)Detect on a nearby iron ball via the annihilation of WIMPs (with themselves) to neutrinos
Review Panel’s Recommendations/Queries:1)What if WIMP’s don’t self annihilate… no answer 2) Hey, you’re `iron ball’ is great for collecting WIMPS via spin-independent scattering, since A of Iron is big (54)! (thanks)3) Funding for preliminary studies...
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Study Results...For SUSY WIMPs… 1) Sun, rate bottleneck is capture not annihilation 2) Earth, situation reversed 3) `Relative Efficiency’ function of WIMP mass
Earth… best whenWIMP mass same as Iron mass… same reason hydrogen is the best neutron moderator
Sun lower masses… little capture
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Solar/Earth Comparison
Annihilation Rate in Earth is Earth Bottleneck
Capture Rate in Earth is Earth Bottlneck (
for
dete
ctor
on
Ear
th)
(WIMP models for spin/scalar comparison)
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Super-Kamiokande’s Results... Upward going muons
Desai, IDM 02
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Transcribe to the Direct Detection Plot Model dependent… but less so than I thought.
Spin-dependent (Sun)
Scalar (Earth)
Desai, IDM 02
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Future Indirect Detectors (neutrino)
Feng, Matchev, Wilczek 2000
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Cosmic Positrons - Halo WIMP annililation HEAT… terrific balloon experiment… saw an excess
Edsjo, IDM 02
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Positron Future… ’s too
Feng, Matchev, Wilczek 2000
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m (
GeV
)
1
103
106
109
1012
10-3
10-6
10-9
1015
1018
1021
Davidson, Hannestad, Raffelt, hep-ph/0001179 Charge Fraction
Excluded Regions
Milli-CHAMP Limits
Overclose Universe(Thermal)
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Stable CHAMPs in Matter
Perl et al., hep-ph/0102033
DM, stop in earth
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Some conclusions Rutherford/Chadwick hunted neutron for 12 years
Hints first seen on continent, interpreted as photons… Neutrino studies started about 90 years ago…
Masses? Majorana? Still not fully nailed down... Dark Matter…
Prepare for a long ride… no physical law guarantees that discoveries happen within any human’s lifetime
The only guarantee: if we fail to look, we will fail to find.