Experimental M. Betz (CERN, Geneva) M. Gasior (CERN, Geneva) searches for axion F. Caspers (CERN, Geneva) M. Thumm (KIT, Karlsruhe) like particles Gentner day 10/2011, CERN, Geneva
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, 2 Geneva 2011
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 10 -6 … > 10 0 eV/c² Mass: 10 17 years Mean lifetime: No interaction with matter! M. Betz; Experimental searches for axion like particles, 3 Geneva 2011
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 expected to be of order 1 Experimental verification The result was puzzling QCD neutrons should have an electrical dipole moment in the Current experimental limit: order of |d N | < 10 -27 e cm |d N | ≈ θ 10 -16 e cm Puzzling questions for QCD-physicists: • Why is the parameter θ so small? (Fine tuning problem!) • Why is there apparently no CP-violation? M. Betz; Experimental searches for axion like particles, 4 Geneva 2011
What is an axion? A solution to the strong CP problem • 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: From: Fermilab Seminar Ultrasensitive Searches for No observation of the axion yet the Axion Karl van Bibber, LLNL January 30, 2008 M. Betz; Experimental searches for axion like particles, 5 Geneva 2011
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 Dark matter distorted? (unknown identity), • Why is the gravitational lensing effect 23% stronger than predicted? Dark energy ( unknown identity), 73% All of those points could be explained by Matter made from assuming there is more matter and energy in our particles we know, universe than we can see 4% 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, 6 Geneva 2011
The Primakoff Effect Axions couple to photons in a strong magnetic field γ can be a photon with energies between μ eV (microwave photon) and up to keV and beyond (gamma quantum) All current experimental searches are based on this * is representing the virtual effect a = axion photons of the magneto-static field From: Fermilab Seminar Ultrasensitive Searches for the Axion Karl van M. Betz; Experimental searches for axion like particles, 7 Bibber, LLNL January 30, 2008 Geneva 2011
Experimental searches around the world Overview Looks for changes in light polarization of a laser Polari- beam in a strong magnetic field zation Looks for axions generated in the sun and sent to Helio- scopes earth Experimental searches for the axion Looks for dark matter axions, uniformly Halo- scopes distributed in our galaxy Light shining Looks for photon axion photon conversions in a trough strong magnetic field the wall M. Betz; Experimental searches for axion like particles, 8 Geneva 2011
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 expected effect is tiny • The polarization is rotated rotation of 3.9 · 10 -12 rad ≈ width of mechanical pencil lead at the distance of the Moon M. Betz; Experimental searches for axion like particles, 9 Geneva 2011
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 http://physicsworld.com/cws/article/news/30423 experimental activities M. Betz; Experimental searches for axion like particles, 10 Geneva 2011
Axion helioscopes The CERN Axion Solar Telescope (CAST) Magnetic field converts axions to X-ray photons Magnetic field converts photons to axions inside the sun • 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, 11 Geneva 2011
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 T N = 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, 12 Geneva 2011
Laser LSW experiments LSW = Light shining through the wall • Some photons 10 20 photons/s < 1 photon/s convert to axions (emitting side) • axions can pass the photons axions photons 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 (Optical resonator cavities) many passes M. Betz; Experimental searches for axion like particles, 13 Geneva 2011
Laser LSW A lot of activity around the world ALPS at DESY (Germany) GRIM REPR at Fermilab (USA) XAX at ESRF (France) OSQUAR at CERN (next door) M. Betz; Experimental searches for axion like particles, 14 Geneva 2011
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 axion helioscope, Igor G Irastorza M. Betz; Experimental searches for axion like particles, 15 Geneva 2011 7th Patras Workshop on Axions, WIMPs and WISPs
Microwaves shining through the wall Cavities become coupled through axions Why microwaves resonators? • High Q-factors around 10 5 (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, 16 Geneva 2011
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, 17 Geneva 2011
The photon conversion cavities Numerical simulation of the TE 011 mode Tuning screw : Possible (20 mm diameter, fine thread) location of an inductive coupling loop for the TE 011 mode (The loop extends on the XY- plane) TE 011 mode, H – field on YZ-plane TE 011 mode, E – field in X-direction TE 011 mode, E – field on XY-plane M. Betz; Experimental searches for axion like particles, 18 Geneva 2011
Electromagnetic shielding Splitting the experiment into two parts Experiment is split into a Environmental RF noise 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 Electric / narrowband microwave signals and will be outside the optical cryostat / magnet converter Shielding Box 2 Optical / electric (Room temp.) converter M. Betz; Experimental searches for axion like particles, 19 Geneva 2011
Recommend
More recommend
![Experimental Design for Simulation Experimental Design for Simulation [Law, Ch. 12][Sanchez et al.](https://c.sambuz.com/680818/experimental-design-for-simulation-s.jpg)
