gray rybka- admx's ongoing search for dark matter axions
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ADMX's Ongoing Searchfor Dark Matter Axions
Gray RybkaUniversity of Washington
Patras Workshop on Axions, WIMPS and WISPsJuly 15, 2009
Durham
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ADMX
Axion Dark Matter eXperimentUniversity of Washington
LLNLUniversity of Florida
UC BerkeleyNRAO
Sheffield University
1) Axion & Dark Matter Review2) ADMX Phase 1 Technology
3) Science Results4) Future Plans
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Axion Vocabulary Review
Axion neutral pseudoscalar particle invented toexplain why QCD is CP-invariant
Axion Mass (ma) single free parameter in
standard axion (~1/fa)
Axion-Photon Coupling (ga) experimentallyaccessible coupling. Mostly fixed by ma.
ga
Peccei, Quinn, Weinberg, Wilczek, etc.
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Axions as Dark Matter
When Peccei-Quinn symmetry is broken, a large numberof axions are produced. (Vacuum misalignment mechanism)
With the right conditions, this makes enough Axions toaccount for dark matter
ma1 meV
Disfavored
by SN1987a
CAST, stellarlimits
Dark MatterSweet Spot
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Prior Dark Matter Axion Limits
ADMX1996 -
2004
ADMX 1996-2004 showedthat we have the sensitivityneeded for axion dark matter
Only a small region of
phase space hasyet been covered
ADMX Phase 1 (2007-2009)Goals:
1) Develop technology to coverDM axion sweet spot quickly2) Expand current limits onaxions
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Dark Matter Axion Cavity Experiments
You Want:-Large Cavity Volume-High Magnetic Field-High Cavity Q
You Don't Want:-High Thermal Noise-High Amplifier Noise
Dark Matter Axions will convertto photons in a magnetic field.
The measurement is enhanced if thephotons frequency correspond to
the cavity's resonant frequency.Sikivie - 1983
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ADMX Design
Cavity Frequency changed by movingmetal rods (not shown) inside cavity
4m
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ADMX Phase 1 New Technology
Field compensation
magnet for SQUIDsSQUID amplifier
The SQUID allows us to lower ournoise temperature (scan faster)
The compensation coil is necessaryfor the SQUID to function
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SQUID Amplifiers
A SQUID converts a magneticflux into a voltage
Over a small range of flux, itacts as an amplifier
The ADMX SQUID uses a microstripresonator to provide the flux, and is thehighest frequency SQUID to date
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The ADMX SQUID
The ADMX SQUID is all about lowering the noise temperature
With the SQUID, noise is limited only by physical temperature(down to 50 mK)
Semiconductor Limit: 2 K
Phase 1 Amplifier (Now)Noise Temperature: 1K
SQUID limit: 50 mK(Planned)
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Technological Performance
The Magnet Ramps up...
The Compensation CoilCancels the Field...
And the SQUIDstill works!
Magnetic Field vs. Time
Field at SQUID vs. Time
Power Spectrum
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Axions to Power Spectra
SQUID
FrequencyMixer
FrequencyMixer
Po
werRods are moved to tune
mass sensitivity
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Data Analysis
Take a 20 KHz scanEvery 90 Seconds
Raw Power Spectrum Receiver Effects Removed
Combine scans into10 MHz nibble
Rescan low SNR areasand candidate axionsEvery week
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What do Axions Look Like?
Sample Axion:
ma=3.48 eV
KSVZ (Qem=1)
dm 0.4 GeV/cm
3
vdisp=220 km/s
vrel=220 km/s
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What Else Looks Like an Axion?
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Current ADMX Phase 1 Sensitivity
Mode crossing
Continued Scanningthrough Fall 2009
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Aside: Chameleons
Chameleon -Chameleon - Scalar or Pseudoscalar that couples tolocal energy density
Interesting property: Mass depends on density of
material around it
Could be important for Dark Energy.
See P. Brax's talk tomorrow for more
Especially interesting: can be trapped inside cavities
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Aside: Chameleons in ADMX
Excite TE011
E&M Mode
in Cavity
E&M mode exciteschameleon mode
Chameleon modedecays back into E&M mode
PowerIn
PowerOut
Turnoff
power
Wait
With the right couplings, ADMX can see chameleon afterglow effect
Expected: Good coupling sensitivity over small mass rangeAnalysis in progress
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What's Next for ADMX?
ADMX Phase 2 Goal
Explore all reasonable dark matter axion models from 1ev to 10eV
How?
Dilution Refrigeratorallows us to reach temperaturesof 50 mK (We're at ~2 K now)
10 times lower temperature= 100 times faster scan speed
-or-10 times faster scan +10 times more sensitiveto ga
1-10 eV coveredin half a year insteadof 50 years
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ADMX Phase 2 and Beyond
Phase 2 will exploredark matter axions in thelowest decade of
plausible mass.
Ideas are in the worksto cover the next twodecades
Dark matter axionscannot hide forever...
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Conclusions
ADMX Phase 1 will expand Dark Matter axionlimits by 0.5 eV
We have demonstrated the functionality of the
SQUID needed to continue to Phase 2 ADMX Phase 2 (2012) will be able to explore
even pessimistic dark matter axion models overa large mass range.
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