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Experimental searches for axion like particles

Experimental searches for axion like particles. Gentner day 10/2011, CERN, Geneva. M. Betz (CERN, Geneva) M. Gasior (CERN, Geneva) F. Caspers (CERN, Geneva) M. Thumm (KIT, Karlsruhe). Outline. What this talk will be about. Introduction to Axions

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Experimental searches for axion like particles

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  1. Experimental searches for axion like particles Gentner day 10/2011, CERN, Geneva M. Betz (CERN, Geneva) M. Gasior (CERN, Geneva) F. Caspers (CERN, Geneva) M. Thumm (KIT, Karlsruhe)

  2. Outline What this talk will be about • Introduction to Axions • Existing experimental searches around the world • The “microwaves shining through the wall” experiment at CERN M. Betz; Experimental searches for axion like particles, Geneva 2011

  3. What is an axion? Introduction • 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 Some properties Charge: None Mass: 10-6 … > 100 eV/c² Mean lifetime: 1017 years No interaction with matter! M. Betz; Experimental searches for axion like particles, Geneva 2011

  4. What is an axion? The strong CP problem • The theory of quantum chromodynamics (QCD) is explicitly CP-violating if one of its parameters θ>0 • θ was expectedtobeof order 1 Puzzling questions for QCD-physicists: • Why is the parameter θ so small? (Fine tuningproblem!) • Why is there apparently no CP-violation?  Experimental verification QCD neutrons should have an electrical dipole moment in the order of |dN| ≈ θ 10-16 e cm • The result was puzzling • Current experimental limit: • |dN| < 10-27 e cm M. Betz; Experimental searches for axion like particles, Geneva 2011

  5. What is an axion? A solution to the strong CP problem • Whatifθis a dynamical variable? • Itwouldoscillatearoundzerolike 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 From: Fermilab Seminar Ultrasensitive Searches for the Axion Karl van Bibber, LLNL January 30, 2008 M. Betz; Experimental searches for axion like particles, Geneva 2011

  6. What is an axion? Also a candidate for dark matter • 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 see • But, 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 M. Betz; Experimental searches for axion like particles, Geneva 2011

  7. The Primakoff Effect Axions couple to photons in a strong magnetic field γcan be a photon with energies between μeV(microwave photon) and up to keVand beyond (gamma quantum) All current experimental searches are based on this effect  * is representing the virtual photons of the magneto-static field a = axion From: Fermilab Seminar Ultrasensitive Searches for the Axion Karl van Bibber, LLNL January 30, 2008 M. Betz; Experimental searches for axion like particles, Geneva 2011

  8. Experimental searches around the world Overview 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 Experimental searches for the axion Looks for dark matter axions, uniformly distributed in our galaxy Looks for photon axion photon conversions in a strong magnetic field M. Betz; Experimental searches for axion like particles, Geneva 2011

  9. Laser polarization experiments PVLAS  (Istituto Nazionale di Fisica Nucleare, Padova, Italy) • 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 The expected effect is tiny rotation of 3.9 · 10-12rad ≈ width of mechanical pencil lead at the distance of the Moon M. Betz; Experimental searches for axion like particles, Geneva 2011

  10. Laser polarization experiments PVLAS  (Istituto Nazionale di Fisica Nucleare, Padova, Italy) • 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 • Nonetheless the publication in 2006 triggered world wide interest and inspired many new experimental activities http://physicsworld.com/cws/article/news/30423 M. Betz; Experimental searches for axion like particles, Geneva 2011

  11. Axion helioscopes The CERN Axion Solar Telescope (CAST) Magnetic field converts axionsto X-ray photons Magnetic field converts photons to axions inside the sun axions 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 M. Betz; Experimental searches for axion like particles, Geneva 2011

  12. Axion helioscopes The Dark Matter eXperiment (ADMX) in Washington • 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 M. Betz; Experimental searches for axion like particles, Geneva 2011

  13. Laser LSW experiments LSW = Light shining through the wall • 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 1020 photons/s < 1 photon/s photons axions photons (Optical resonator cavities) M. Betz; Experimental searches for axion like particles, Geneva 2011

  14. Laser LSW A lot of activity around the world ALPS at DESY (Germany) XAX at ESRF (France) GRIM REPR at Fermilab (USA) OSQUAR at CERN (next door) M. Betz; Experimental searches for axion like particles, Geneva 2011

  15. Experimental searches around the world Results so far: No axion has been observed yet Laser polarization Laser LSW Sensitivity (ADMX) Mass Towards a new generation axionhelioscope, Igor G Irastorza 7th Patras Workshop on Axions, WIMPs and WISPs M. Betz; Experimental searches for axion like particles, Geneva 2011

  16. Microwaves shining through the wall Cavities become coupled through axions 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 exists But: • The “wall” becomes a faraday cage  EMI shielding challenge γ Photon a Axion EM. Electromagnetic M. Betz; Experimental searches for axion like particles, Geneva 2011

  17. The photon conversion cavities Prototypes after machining (left) and coating (right) Fine thread tuning screw Coupler (β=1) Material: Brass (non magnetic) M. Betz; Experimental searches for axion like particles, Geneva 2011

  18. The photon conversion cavities Numerical simulation of the TE011 mode Tuning screw: (20 mm diameter, fine thread) Possible location of an inductive coupling loop for the TE011 mode (The loop extends on the XY-plane) TE011 mode, E–field in X-direction TE011 mode, H–field on YZ-plane TE011 mode, E–field on XY-plane M. Betz; Experimental searches for axion like particles, Geneva 2011

  19. Electromagnetic shielding Splitting the experiment into two parts Environmental RF noise • Experiment is split into a cryogenic and room temperature part Shielding Box 1 (Cryo.) Shielding Box 1 Contains the Axion detection cavity and will later be placed in the cryostat / magnet Optical Fibre Carries the weak signal from Axion conversion to the measurement instruments, unaffected by ambient EM. noise and without comprising the shielding boxes Shielding Box 2 Contains instruments for the detection of weak narrowband microwave signals and will be outside the cryostat / magnet Electric / optical converter Shielding Box 2 (Room temp.) Optical / electric converter M. Betz; Experimental searches for axion like particles, Geneva 2011

  20. Electromagnetic shielding Some practical aspects • EM absorbing material between shielding layers (non magnetic!) • Chain of lowpassfeedtrough 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 Optical power converter VCC High power Laser diode M. Betz; Experimental searches for axion like particles, Geneva 2011

  21. DC – feedtrough filters For feeding DC power through the shielding while keeping RF out Syfer SFJNC2000684MX1 Measurement with a network analyser in transmission - 95 dB at 3 GHz M. Betz; Experimental searches for axion like particles, Geneva 2011

  22. Electromagnetic shielding Shielding box 1 prototype, containing the receiving cavity M. Betz; Experimental searches for axion like particles, Geneva 2011

  23. Debugging of the faraday cage The current status in the laboratory E.M. leakage test setup • 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 M. Betz; Experimental searches for axion like particles, Geneva 2011

  24. Electromagnetic shielding Shielding box 2 prototype, containing the instrumentation E.M. leakage test setup • Feedtrough for optical fibres • Receiving cavity • Spectrum analyzer • Low noise amplifier M. Betz; Experimental searches for axion like particles, Geneva 2011

  25. Online diagnostics Supervising the shielding attenuation with test tones 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 • 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) M. Betz; Experimental searches for axion like particles, Geneva 2011

  26. Online diagnostics Possible signal-paths • All possible signal paths are represented as arrows • Green signalspass one shielding layer and can be used to quantify its attenuation • Red signalspass more than one shielding layer. Observation of a red signal = veto condition on Axion detection Shieldingbox Attenuation of the Shieldingbox is measured twice, giving us redundancy M. Betz; Experimental searches for axion like particles, Geneva 2011

  27. Detecting weak narrowband signals Homodyne detection with an commercial vector signal analyser • To detect signals down to -230 dBm we need resolution bandwidths in the 10 μHz range • Thiscanbeachievedwith a FFT on a 24 h time trace • Frequencydriftsareunavoidable! • But byphaselockingsourceandanalyzerwecaneliminate relative frequencyerrors Vector signal analyser (Agilent N9010A EXA) Common reference clock M. Betz; Experimental searches for axion like particles, Geneva 2011

  28. Photon regeneration exp. at CERN Technical specifications and challenges for hidden photon search 300 dB Expected signal power from the receiving cavity arXiv:0707.2063v1 F. Caspers, J. Jaeckel, A. Ringwald, A Cavity Experiment to Search for Hidden Sector Photons M. Betz; Experimental searches for axion like particles, Geneva 2011

  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

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