Experimental searches for axion like particles

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


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!


• 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


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


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


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


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


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


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

http://physicsworld.com/cws/article/news/30423


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


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


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)


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)


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


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


The photon conversion cavities

Prototypes after machining (left) and coating (right)

Material: Brass (non magnetic)Fine thread tuning screw Coupler (β=1)


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)


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


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


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


Electromagnetic shieldingShielding box 1 prototype, containing the receiving cavity


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


Electromagnetic shieldingShielding box 2 prototype, containing the instrumentation

• Feedtrough for optical fibres

• Receiving cavity

• Spectrum analyzer

• Low noise amplifier

E.M. leakagetest setup


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)


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


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


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

Experimental searches for axion like particles

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