Dark Matter Overview
Harry Nelson
UCSB
INPAC
Oct. 4, 2003
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Outline Axions Massive Particles
Direct Detection Weakly Interacting No Strongly Interacting (interesting opportunities)
See talks of Dave Cline (ZEPLIN), Patrizia Meunier (CDMS-II)
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Usual Simplifications of Dark Matter Local energy density, speed of DM
Consists of one elementary particle (!)
ú0 ø 300cm3
MeVv0 ø 220
skm
(ì 0 ø 7â 10à 4)
0? (200-2000) (170-270)… from galactic astrophysics
, e,e- , p , n - 7 in our few percent of Univ.2 are composite… n ??
The DM particle that provides the clearest signal in a search might not be the most abundant – a strong argument for an eclectic mix of search techniques.
(ì 20 ø
21 â 10à 6)
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Advice of Dennis the Menace
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DM not baryons (CBR, BBN; Eros/MACHO) DM was once in thermal equibrium
Usual Simplifications of Dark Matter
mass > few keV (large scale structure)mass < 340 TeV (unitarity)
cross section with us weak (10-44-10-36 cm2)…little unknown missing energy at LEP, Tevatron… mass>10’s GeV
SUSY restored just above weak scale gives WIMPS
Weakly Interacting Massive Particles
DM at rest:vDM=0 (sun plowing through at v0 220 km/s)
vDM1/2 300 km/s… useful to approximate 02
…Attractive candidates (axions, `*zillas’, etc.) were never in thermal equilibrium…
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a axion, couples to … non- thermal, very light
Round up the Usual Suspects
e e- 0 p n -- Our Matter
0 (SUSY, neutralino, WIMP)
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Direct Detection Momentum Transfer
v0
Convert a to photon – detect it
axion
m v0 target
Cause target recoil – detect it
MassiveParticle
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Axions (and similar)
(Dark matter)axion models
1.9-3.4 eV (ADMX, LLNL-Florida-Berkeley-NRAO)
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Primakoff Conversion, Microwave Detection
Solenoid
Amplifier – power pours out of cavity when B0 applied
Cavity, `TM’ mode(E parallel to B0: 0- )
LB= 50 cm
Lower noise allows faster scanning….
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Signal Level and Noise10-17 W fromPioneer 10Spacecraft,1010 km away
HEMT 10-26 W
(s
/n)
(time)
Substantial improvements in Ts are on the horizon (X30) from increased cooling, SQUIDS
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Nuclear Recoil – Cross Section
A4
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WIMP Region Large Exposure, Background:DAMA (58K kg-days, NaI)ZEPLIN (230 kg-days, Xe)IGEX (276 kg-days, Ge Ioniz)
Small Exposure, Background:CDMS (28 kg-days, Ge P/I)Edelweiss (12 kg-days, Ge P/I)(DRIFT - gaseous, recoil dir.)
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Event Rates...
RickGaitskell
Xe Nuclear Form Factor
~ several 10-2 ev/kg/d/keV
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Compare with Common Background Rate
• Shield (shield radioactive too!)… 1 ev/(kg d keV) typical• Reduce the background… HDMS , IGEX , Genius (Ge Ionization)• Exploit astron. properties (year cycle, directionality) DAMA, DRIFT• Devise detectors that can distinguish nuclear recoil from electron recoil… Edelweiss, CDMS, Xenon..
DRU
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vDM1/2 300 km/s2
vDM1/2 =0 km/s2
DAMA: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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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
I
3
4
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DAMA vs. Super-K Model dependent… but less so than I thought.
Spin-dependent (Sun)
Scalar (Earth)
Desai, IDM 02
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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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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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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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CDMS-II Projections
~1cal year, initial deployment
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Some conclusions Axions searches about to become much more
sensitive WIMPs…
Next few years should get factor of 100 sensitivity High Mass, Bkgd versus Low Mass, Bkgd:
How well do very high mass detectors self shield?Can low mass, bkgd be mass produced with ever-lower
background requirements? Is Xe, with ionization, `middle way’?
INPAC...