TAUP 2009 Rome Axion Searches Leslie J Rosenberg University of Washington Department of Physics July 2, 2009
Talk outline Basic axion properties Selected searches: (see, e.g., parallel sessions for more …) 5th force searches Photon regeneration and optical rotation Solar axion searches RF cavity (dark-matter axions) Overall status of axion searches * Special thanks for Prof. Karl van Bibber for information and slides
Axions and axion-like particles e.g., Majoron (from lepton-number breaking…neutrino masses) Familon (from family-symmetry breaking) Dilaton (low-lying excitation in string theory) Axion (removes CP violation in strong interactions) Axions are well-motivated and their phenomenology is well-understood
Properties of the axion The axion is a light pseudoscalar resulting from the broken “Peccei-Quinn” symmetry to enforce Strong CP conservation f a , the SSB scale the PQ symmetry breaking, is the one important parameter of the theory.
More on axion masses and couplings 10 –8 The axion is a light cousin of π 0 : J π = 0 – 10 –10 γ Horizontal Branch g a γγ (GeV –1 ) Star limit a 10 –12 Ω a > 1 Sn1987a –1 ∴ g a γγ ∝ m a m a , g aii ∝ f a 10 –14 7/6 → m a > 1 µ eV Ω a ∝ f a Axion models 10 –16 Sn1987a ν pulse precludes NN → NNa for m a ~10 –(3–0) eV 10 0 10 –6 10 –4 10 –2 m a (eV) Red giant evolution precludes Good news – Parameter space is bounded g a γγ > 10 –10 GeV –1 Bad news – All couplings are extraordinarily weak
Wilczek on axions and dark matter (Physics Today, Oct. ‘ 03) “…I'm much more optimistic about the dark matter problem. Here we have the unusual situation that two good ideas exist – which, according to William of Occam (the razor guy), is one too many. “The symmetry of the standard model can be enhanced, and some of its aesthetic shortcomings can be overcome, if we extend it to a larger theory. Two proposed extensions, logically independent of one another, are particularly specific and compelling. “One incorporates a symmetry suggested by Roberto Peccei and Helen Quinn in 1977. Peccei-Quinn symmetry rounds out the logical structure of quantum chromodynamics by removing QCD's potential to support strong violation of time-reversal symmetry, which is not observed. This extension predicts the existence of a remarkable new kind of very light, feebly interacting particle: the axion. …
The special role of axion-photon mixing in sensitive searches L int = ag a �� E � B Laboratory Dark matter (“laser”) Solar P. Sikivie, PRL 51, 1415 (1983) See Raffelt & Stodolsky for general treatment of axion-photon mixing – PRD 37, 1237 (1988)
5 th force searches: Distances less than 100 µ m Axions mediate matter-spin couplings ) e � r / � � � ˆ ( V ~ 1/ r r a g s i γ 5 g p ψ 1 ψ 2 Not very sensitive, but generic
Vacuum birefringence & dichroism Vacuum dichroism ε ~ N ⋅ (1/4 gB 0 L) 2 (N = number of passes) ε Fabry- B 0 Perot Laser Magnet Ψ l + Vacuum birefringence Ψ = N ·(1/96)·(g B 0 m a ) 2 ·L 3 / ω Maiani, Zavattini, Petronzio, Phys. Lett. B 175 (1986) 359
Example: The PVLAS experiment (INFN Legnaro) E. Zavattini et al., PRL 96 (2006) 110406 Y.Semertzidis et al., PRL 64 (1990) 2998 M = 1/g a γγ 1 ω 2 ω
Recent PVLAS details & data PVLAS Schematic Phase-Amplitude Plot Rebuilt detector doesn ’ t find signal. Their early value of g a γγ was ostensibly excluded already by 4 orders of magnitude, by CAST, and stellar evolution (stars would live only a few thousand years) The allowed region is on the very fringe of the exclusion region of the earlier RBF polarization experiment, plus the photon regeneration experiment Nevertheless, this renewed polarization-rotatation experiments around the world, and much theoretical work
Photon regeneration (“shining light through walls”) Van Bibber et al., PRL 59 Photon Wall B 0 B 0 (1987) 759 Detector γ a Laser Magnet Magnet L L g a γγ (GeV -1 ) P( γ→ a →γ ) ~ 1/16 (gB 0 L) 4 Only measurement to date: g < 6.7 x 10 -7 GeV -1 for m a < 1 meV G. Ruoso et al., Z. Phys. C. 56, 505 (1992) & R. Cameron et al., Phys. Rev. D47, 3707 (1993) m a (eV)
Several photon regeneration efforts around the world Experiments in various phases of prepation or operation CERN Courier, Vol. 47 No. 2 (March 2007) All of them would still be orders of magnitude away from CAST/HBS limits
Resonantly enhanced photon regeneration Basic concept – encompass the production and regeneration magnet regions with Fabry-Perot optical cavities, actively locked in frequency Photon Sikivie, Tanner, van Bibber PRL (April 27, 2007) Detectors IO Laser Magnet Magnet Matched Fabry-Perots P Re sonant ( � � a � � ) = 2 2 � � P Simple ( � � a � � ) = F � P Simple ( � � a � � ) � 2 F � � � where η , η ’ are the mirror transmissivities & F, F ’ are the finesses of the cavities For η ~ 10 (5-6) , the gain in rate is of order 10 (10-12) γγ improves by 10 (2.5–3) and the limit in g a γγ
Solar axion search γ a Produced by a Primakoff interaction, with a γ∗ γ∗ mean energy of 4.2 keV Ze solar-axion spectrum T central = 1.3 keV, but plasma screening Flux [10 10 m a (eV) 2 cm -2 sec -1 keV -1 ] suppresses low energy part of spectrum 16 The total flux (for KSVZ axions) at the Earth is given by � a = 7.44 � 10 11 cm � 2 sec � 1 ( m a /1 eV ) 2 The dominant contribution is confined to the central 20% of the Sun ’ s radius 0 10 E [ keV ]
Principle of the solar-axion search experiment Photon B 0 Detector a Magnet l γ a B x � ( a � � ) = 1 4 ( g a �� B 0 L ) 2 F ( q ) 2 L a �� = ag a �� E � B 2 /2 � F ( q ) = Sin ( qL /2) q = k � � k a � m a , and F (0) = 1 where ( qL /2)
Example: The CERN Axion Solar Telescope (CAST) a γ Prototype LHC dipole magnet, double bore, 50 tons, L~10m, B~10T Tracks the Sun for 1.5 hours at dawn & 1.5 hours at dusk Instrumented w. 3 technologies: CCD w. x-ray lens; Micromegas; TPC
CAST results and future CAST has published results equalling the Horizontal Branch Star limit (Red Giant evolution) They are pushing the mass limit up into the region of axion models, 0.1- 1 eV CAST JCAP Plan: Fill the magnet bore with gas (e.g. helium), and tune the pressure When the plasma frequency equals the axion mass, full coherence and conversion probability are restored: � p = (4 �� N e / m e ) 1/ 2 � m � K. Zioutas et al., Phys. Rev. Lett. 94 , 121301 (2005) KvB, P. McIntyre, D. Morris, G. Raffelt PRD 39 (1989) 2085 They will go to higher m a with 3 He, and a second x-ray optic
RF cavity axion-search experiments: Axion and electromagnetic fields exchange energy The axion-photon coupling… g a γ …is a source in Maxwell ’ s Equations � E 2 /2 ( ) ( ) = g a � ˙ ( ) � E � � � B a E � B � t So imposing a strong external magnetic field B allows the axion field to pump energy into the cavity.
How to detect dark-matter axions Important to lower Ts
ADMX: Axion Dark-Matter eXperiment U of Washington, LLNL, University of Florida, UC Berkeley, National Radio Astronomy Observatory Magnet with insert (side view) Magnet arrives
ADMX hardware high-Q cavity experiment insert
The axion receiver
The world ’ s quietest radio receiver Systematics-limited for signals of 10 -26 W ~10 -3 of DFSZ axion power (1/100 yoctoWatt).
Recent published data Astrophysics Particle Physics Ap.J These are interesting regimes of particle and astrophysics: probe realistic axion couplings and halo densities
Lower T s : SQUID Amplifiers I B The basic SQUID amplifier is a flux- to-voltage transducer V o (t) Φ SQUID noise arises from Nyquist noise in shunt resistance scales linearly with T However, SQUIDs of conventional design are poor amplifiers above 100 MHz (parasitic couplings). Flux-bias to here
Quantum-limited gigahertz SQUID amplifiers 4 Noise Temperature (mK) SQUID A2-5, f = 684 MHz SQUID L1-3, f = 642 MHz Semiconductor 2 SQUID K4-2, f = 702 MHz 1000 6 4 T QL 2 100 Clarke and Kinion 6 4 quantum limit 2 2 4 6 8 2 4 6 8 2 4 100 1000 An old idea from antenna design Physical Temperature (mK) (“shunt detuned frequency”) applied to quantum electronics.
SQUID commissioning calibration
ADMX achieved and target sensitivity Definitive sensitivity over lowest decade in mass (where dark matter axions would likely be) Plus operations into second decade of mass (where unusual axions might be)
Overall status of axion hunting CAST SN1987A ADMX Upgrade
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