experimental searches for axion like particles m. betz (cern, geneva) m. gasior (cern, geneva) f....
DESCRIPTION
What is an axion? A hypothetical elementary particle Postulated by R. Peccei, H. Quinn, S. Weinberg and F. Wilczek in 1977 – 1978 to explain the strong CP-violation A candidate for dark matter in our universe Also a washing detergent 3 Introduction M. Betz; Experimental searches for axion like particles, Geneva 2011 Some properties Charge:None Mass:10 -6 … > 10 0 eV/c² Mean lifetime:10 17 years No interaction with matter! Some properties Charge:None Mass:10 -6 … > 10 0 eV/c² Mean lifetime:10 17 years No interaction with matter!TRANSCRIPT
Experimental searches for axion like particles
M. Betz (CERN, Geneva)M. Gasior (CERN, Geneva)F. Caspers (CERN, Geneva)
M. Thumm (KIT, Karlsruhe)
Gentner day10/2011, CERN, Geneva
2M. Betz; Experimental searches for axion like particles, Geneva 2011
Outline
• Introduction to Axions
• Existing experimental searches around the world
• The “microwaves shining through the wall” experiment at CERN
What this talk will be about
3M. Betz; Experimental searches for axion like particles, Geneva 2011
What is an axion?
• A hypothetical elementary particle• Postulated by R. Peccei, H. Quinn, S. Weinberg
and F. Wilczek in 1977 – 1978 to explain the strong CP-violation
• A candidate for dark matter in our universe• Also a washing detergent
Introduction
Some properties
Charge: NoneMass: 10-6 … > 100 eV/c²Mean lifetime: 1017 yearsNo interaction with matter!
4M. Betz; Experimental searches for axion like particles, Geneva 2011
• The theory of quantum chromodynamics (QCD) is explicitly CP-violating if one of its parameters θ>0
• θ was expected to be of order 1
Puzzling questions for QCD-physicists:• Why is the parameter θ so small? (Fine tuning problem!)• Why is there apparently no CP-violation?
What is an axion?The strong CP problem
The result was puzzling
Current experimental limit:
|dN| < 10-27 e cm
Experimental verificationQCD neutrons should have an electrical dipole moment in the order of
|dN| ≈ θ 10-16 e cm
5M. Betz; Experimental searches for axion like particles, Geneva 2011
What is an axion?
• What if θ is a dynamical variable?• It would oscillate around zero like a
pendulum• This would eliminate CP violating terms
from the QCD-Lagrangian• The oscillations can be seen as new
particle The axion• So far the most elegant and widely
accepted solution to the strong CP-problem
• For theoretical physics: Problem solved!
• But in experimental physics:No observation of the axion yet
A solution to the strong CP problem
From: Fermilab Seminar Ultrasensitive Searches for the Axion Karl van Bibber, LLNL January 30, 2008
6M. Betz; Experimental searches for axion like particles, Geneva 2011
What is an axion?Also a candidate for dark matter
Dark energy (unknown identity),
73%
Dark matter (unknown identity), 23%
Matter made from par-ticles we know,
4%
Some puzzling question for astrophysicists:• Why do clusters of galaxies rotate faster on
their outskirts than they should?• Why does the cosmic microwave background
radiation appear to be distorted?• Why is the gravitational lensing effect stronger
than predicted?
All of those points could be explained by assuming there is more matter and energy in our universe than
we can seeBut, what is this dark matter made of?
Axions are excellent candidates for dark matter
Note that axions could exist, even if the dark matter theory would be disproven
7M. Betz; Experimental searches for axion like particles, Geneva 2011
The Primakoff Effect
Axions couple to photons in a strong magnetic field
From: Fermilab Seminar Ultrasensitive Searches for the Axion Karl van Bibber, LLNL January 30, 2008
* is representing the virtual photons of the magneto-static field
γ can be a photon with energies between μeV
(microwave photon) and up to keV and
beyond(gamma quantum)
a = axion
All current experimental searches are based on this
effect
8M. Betz; Experimental searches for axion like particles, Geneva 2011
Experimental searches around the world
Polari-
zationHelio-scope
sHalo-scope
sLight shinin
g trough the wall
Overview
Experimentalsearches for the
axion
Looks for changes in light polarization of a laser beam in a strong magnetic field
Looks for axions generated in the sun and sent to earth
Looks for dark matter axions, uniformly distributed in our galaxy
Looks for photon axion photon conversions in a strong magnetic field
9M. Betz; Experimental searches for axion like particles, Geneva 2011
Laser polarization experiments
• Linear polarized laser beam transverses strong magnetic field
• The component parallel to the magnetic field is converted to hidden particles (primakoff effect) selective absorption
• The polarization is rotated
PVLAS (Istituto Nazionale di Fisica Nucleare, Padova, Italy)
The expected effect is tinyrotation of 3.9 · 10-12 rad
≈ width of mechanical pencil leadat the distance of the Moon
10M. Betz; Experimental searches for axion like particles, Geneva 2011
Laser polarization experiments
• In 2006 the PVLAS collaboration published their results
• They claimed to have observed the effect they were looking for
• After an update of the detector, the results could not be confirmed
PVLAS (Istituto Nazionale di Fisica Nucleare, Padova, Italy)
http://physicsworld.com/cws/article/news/30423
Nonetheless the publication in 2006 triggered world wide
interest and inspired many new experimental activities
11M. Betz; Experimental searches for axion like particles, Geneva 2011
Axion helioscopes
Magnetic field converts photons to axions inside the sun
The CERN Axion Solar Telescope (CAST)
Magnetic field converts axions to X-
ray photonsaxions
photons
•Prototype LHC magnet, 10 m long, 9 Tesla on a movable platform•Tracks the sun for 3h / day, 50 days / year•X-ray focusing system (prototype from the space based X-ray telescope ABRIXAS)•X-ray detectors (micromegas, CCD) at both ends of the magnet•Has been running since 2003 and is now waiting for an upgrade in 2012
12M. Betz; Experimental searches for axion like particles, Geneva 2011
Axion helioscopes
• Assumes: Axions are dark matter, a relic from the big bang and already all around us
• 8 T Magnet converts relic axions to microwave photons
• Tunable cavity 460 – 810 MHz to “collect” those photons
• SQUID amplifier, system noise temperature TN = 2.5 K, one of the quietest microwave receivers in the world
• Running since 2006 (at LLNL), moved to University of Washington in 2010, upgrade of cryo system this year
The Dark Matter eXperiment (ADMX) in Washington
13M. Betz; Experimental searches for axion like particles, Geneva 2011
Laser LSW experimentsLSW = Light shining through the wall
1020 photons/s < 1 photon/s• Some photons convert to axions (emitting side)
• axions can pass the wall
• Some axions convert back to photons (detection side)
• It seems like light is shining through the wall!
• Fabry-Perot cavities allow to enhance the probability: photons make many passes
photons axions photons
(Optical resonator cavities)
14M. Betz; Experimental searches for axion like particles, Geneva 2011
Laser LSWA lot of activity around the world
ALPS at DESY (Germany)
OSQUAR at CERN (next door)XAX at ESRF (France)
GRIM REPR at Fermilab (USA)
15M. Betz; Experimental searches for axion like particles, Geneva 2011
Experimental searches around the worldResults so far: No axion has been observed yet
Towards a new generation axion helioscope, Igor G Irastorza7th Patras Workshop on Axions, WIMPs and WISPs
Laser LSW
(ADMX)
Laser polarization
Sensitivity
Mass
16M. Betz; Experimental searches for axion like particles, Geneva 2011
Microwaves shining through the wall
Why microwaves resonators?• High Q-factors around 105 (low
loss) are easily achieved• Easier construction /
alignment• Homodyne detection methods
can be applied (very sensitive)• Instruments and know-how
existsBut:• The “wall” becomes a faraday
cage EMI shielding challenge
Cavities become coupled through axions
γ Photona AxionEM. Electromagnetic
17M. Betz; Experimental searches for axion like particles, Geneva 2011
The photon conversion cavities
Prototypes after machining (left) and coating (right)
Material: Brass (non magnetic)Fine thread tuning screw Coupler (β=1)
18M. Betz; Experimental searches for axion like particles, Geneva 2011
TE011 mode, H–field on YZ-plane
The photon conversion cavitiesNumerical simulation of the TE011 mode
Possible location of
an inductive coupling
loop for the TE011 mode
(The loop extends on
the XY-plane)
TE011 mode, E–field on XY-plane
TE011 mode, E–field in X-direction
Tuning screw:(20 mm diameter, fine thread)
19M. Betz; Experimental searches for axion like particles, Geneva 2011
Electromagnetic shielding
Experiment is split into a cryogenic and room temperature part
Splitting the experiment into two parts
Electric / optical
converter
Optical / electric
converter
Shielding Box 1Contains the Axion detection cavity and will later be placed in the cryostat / magnet
ShieldingBox 1
(Cryo.)
Optical FibreCarries the weak signal from Axion conversion to the measurement instruments, unaffected by ambient EM. noise and without comprising the shielding boxes
Shielding Box 2Contains instruments for the detection of weak narrowband microwave signals and will be outside the cryostat / magnet
Shielding Box 2(Room temp.)
EnvironmentalRF noise
20M. Betz; Experimental searches for axion like particles, Geneva 2011
Electromagnetic shielding
• EM absorbing material between shielding layers (non magnetic!)
• Chain of lowpass feedtrough filters for supply voltage
If we still see leakage:• Power over optical fibre
– Commercial systems available (JDSU Photonic power module)
– Efficiency 50 %(optical electric)
• We can always add another layer of shielding
Some practical aspects
High powerLaser diode
VCC
Optical powerconverter
21M. Betz; Experimental searches for axion like particles, Geneva 2011
DC – feedtrough filtersFor feeding DC power through the shielding while keeping RF out
Measurement with a network analyser in transmission
- 95 dB at 3 GHz
Syfer SFJNC2000684MX1
22M. Betz; Experimental searches for axion like particles, Geneva 2011
Electromagnetic shieldingShielding box 1 prototype, containing the receiving cavity
23M. Betz; Experimental searches for axion like particles, Geneva 2011
Debugging of the faraday cage
• Phase locked RF – Source (3 GHz)
• Optical receiver for 10 MHz phase lock signal
• 50 W RF power amplifier
• Custom made EMI - feed trough filter for AC power
• Faraday cage, containing detection part
• Fibre optical converter for control signals
• Multimeter for tuning the cavity
• Emitting cavity
The current status in the laboratory
E.M. leakagetest setup
24M. Betz; Experimental searches for axion like particles, Geneva 2011
Electromagnetic shieldingShielding box 2 prototype, containing the instrumentation
• Feedtrough for optical fibres
• Receiving cavity
• Spectrum analyzer
• Low noise amplifier
E.M. leakagetest setup
25M. Betz; Experimental searches for axion like particles, Geneva 2011
Online diagnostics
Test tones (TXn) Low power (μW) probe signals Injected in laboratory space and
between shielding layers Each one has a slightly different
frequency within the cavity bandwidth
Monitoring signal power (RXn) allows to quantify the attenuation of each shielding layer
Supervising the shielding attenuation with test tones
We need ONLINE diagnostics showing, that the shielding performance is really maintained over the full lifetime of the experiment. Degradation
is possible due to bad and ageing contacts
If dynamic range of the receivers is not sufficient, time multiplexing is an option.
(Sender and receiver in the same shielding shell are not enabled at the same time)
26M. Betz; Experimental searches for axion like particles, Geneva 2011
Online diagnostics
• All possible signal paths are represented as arrows• Green signals pass one shielding layer and can be
used to quantify its attenuation• Red signals pass more than one shielding layer.
Observation of a red signal = veto condition on Axion detection
Possible signal-paths
Attenuation of the Shieldingbox is measured
twice, giving us redundancy
Shieldingbox
27M. Betz; Experimental searches for axion like particles, Geneva 2011
Detecting weak narrowband signalsHomodyne detection with an commercial vector signal analyser
Common reference clock
Vector signal analyser (Agilent N9010A EXA)
• To detect signals down to -230 dBm we need resolution bandwidths in the 10 μHz range
• This can be achieved with a FFT on a 24 h time trace• Frequency drifts are unavoidable!• But by phase locking source and analyzer we can eliminate relative frequency errors
28M. Betz; Experimental searches for axion like particles, Geneva 2011
Photon regeneration exp. at CERNTechnical specifications and challenges for hidden photon search
Expected signal power from the receiving cavity
arXiv:0707.2063v1F. Caspers, J. Jaeckel, A. Ringwald, A Cavity Experiment to Search for Hidden Sector Photons
What we want to achieve (for HSPs):
Pem 50 W = 47 dBm Signal power into emitting cavity
Pdet 10-26 W = -230 dBm Signal power from receiving cavity
Q 23 000 Quality factor emitting cavity
Q‘ 23 000 Quality factor receiving cavity
G ≈ 0.5 HSP. geometry factor
mγ’ 12 μeV ≈ 3 GHz Hidden photon mass
ω0 3 GHz Cavity resonance frequency
Χ 1.1 · 10-9 Coupling factor (exclusion limit) 300 dB
29
Acknowledgements
• The author would like to thank the CERN BE and BI-dept. management for support as well as R. Jones and R. Heuer for encouragement
• Many thanks to A. Ringwald, A. Lindner and J. Jäckel for a large number of hints as well as and K. Zioutas for having brought the right people in the right moment together as well as haven given very helpful comments
M. Betz; Experimental searches for axion like particles, Geneva 2011