Axion Searches Leslie J Rosenberg University of Washington - - PowerPoint PPT Presentation

Leslie J Rosenberg University of Washington Department of Physics July 2, 2009

TAUP 2009 Rome

Axion Searches

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 fa, the SSB scale the PQ symmetry breaking, is the one important parameter of the theory.

ma , gaii ∝ fa

–1 ∴ gaγγ ∝ ma

Axion models

More on axion masses and couplings

10–6 10–4 10–2 100 ma (eV) 10–16 10–14 10–12 10–8 10–10 gaγγ (GeV–1)

The axion is a light cousin of π0: Jπ= 0– a

γ Ωa ∝ fa

7/6 → ma > 1 µeV

Ωa > 1

Sn1987a ν pulse precludes NN→NNa for ma~10–(3–0) eV Sn1987a Horizontal Branch Star limit Red giant evolution precludes

gaγγ > 10–10 GeV–1 Good news – Parameter space is bounded 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

• ut

the logical structure

• f

quantum chromodynamics by removing QCD's potential to support strong violation of time-reversal symmetry, which is not

• bserved. 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

Dark matter Solar Laboratory (“laser”)

• P. Sikivie, PRL 51, 1415 (1983)

See Raffelt & Stodolsky for general treatment of axion-photon mixing – PRD 37, 1237 (1988)

Lint = aga E B

5th force searches: Distances less than 100 µm

Axions mediate matter-spin couplings

ψ1

V ~ 1/r

( )er / ˆ

r

ψ2 a gs iγ5gp

Not very sensitive, but generic

Vacuum birefringence & dichroism

l

B0 Magnet Laser

ε

+

Ψ

Fabry- Perot

ε ~ N ⋅ (1/4 gB0L)2 (N = number of passes)

Maiani, Zavattini, Petronzio, Phys. Lett. B 175 (1986) 359

Vacuum dichroism Vacuum birefringence

Ψ = N ·(1/96)·(g B0ma)2·L3/ω

Example: The PVLAS experiment (INFN Legnaro)

1ω 2ω M = 1/gaγγ

• E. Zavattini et al., PRL 96 (2006) 110406

Y.Semertzidis et al., PRL 64 (1990) 2998

Recent PVLAS details & data

PVLAS Schematic Phase-Amplitude Plot

Rebuilt detector doesn’t find signal. Their early value of gaγγ 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”)

Wall

Photon Detector

a γ

Laser

L B0 Magnet B0 Magnet L

Van Bibber et al., PRL 59 (1987) 759

Only measurement to date: g < 6.7 x 10-7 GeV-1 for ma < 1 meV

• G. Ruoso et al., Z. Phys. C. 56, 505 (1992) &
• R. Cameron et al., Phys. Rev. D47, 3707 (1993)

ma (eV)

gaγγ (GeV-1)

P(γ→a→γ) ~ 1/16 (gB0L)4

Several photon regeneration efforts around the world

CERN Courier, Vol. 47 No. 2 (March 2007) Experiments in various phases of prepation or operation

All of them would still be orders of magnitude away from CAST/HBS limits

Resonantly enhanced photon regeneration

Sikivie, Tanner, van Bibber PRL (April 27, 2007)

Matched Fabry-Perots IO

Laser Magnet Magnet

Photon Detectors

Basic concept – encompass the production and regeneration magnet regions with Fabry-Perot optical cavities, actively locked in frequency

P Resonant( a ) = 2 P Simple( a ) = 2 2 F F P Simple( a )

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) and the limit in gaγγ

γγ improves by 10(2.5–3)

Produced by a Primakoff interaction, with a mean energy of 4.2 keV Tcentral = 1.3 keV, but plasma screening suppresses low energy part of spectrum The total flux (for KSVZ axions) at the Earth is given by The dominant contribution is confined to the central 20% of the Sun’s radius

Solar axion search

E [ keV ] 16 Flux [1010 ma(eV)2 cm-2 sec-1 keV-1 ] 10

γ γ∗ γ∗ a

Ze

a = 7.44 1011cm2 sec1(ma /1eV)2

solar-axion spectrum

Principle of the solar-axion search experiment l

B0 Magnet Photon Detector a

γ B a

x

La = aga E B

(a ) = 1 4 (gaB0L)2 F(q)

2

F(q) = Sin(qL /2) (qL /2)

F(0) =1

,

q = k ka ma

2 /2

where and

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

• K. Zioutas et al., Phys. Rev. Lett. 94, 121301 (2005)

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 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 = (4Ne /me)1/ 2 m

They will go to higher ma with 3He, and a second x-ray optic

KvB, P. McIntyre, D. Morris, G. Raffelt PRD 39 (1989) 2085 CAST JCAP

RF cavity axion-search experiments: Axion and electromagnetic fields exchange energy

The axion-photon coupling… …is a source in Maxwell’s Equations

E2 /2

( )

t E B

( ) = ga ˙

a E B

( )

So imposing a strong external magnetic field B allows the axion field to pump energy into the cavity. gaγ

How to detect dark-matter axions

Important to lower Ts

ADMX: Axion Dark-Matter eXperiment

Magnet with insert (side view) Magnet arrives

U of Washington, LLNL, University of Florida, UC Berkeley, National Radio Astronomy Observatory

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

Particle Physics Astrophysics

These are interesting regimes of particle and astrophysics: probe realistic axion couplings and halo densities

Ap.J

Lower Ts: SQUID Amplifiers

IB Vo (t)

Φ The basic SQUID amplifier is a flux- to-voltage transducer 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

An old idea from antenna design (“shunt detuned frequency”) applied to quantum electronics.

2 4 6

100

2 4 6

1000

2 4

Noise Temperature (mK)

2 4 6 8

100

2 4 6 8

1000

2 4

Physical Temperature (mK)

SQUID A2-5, f = 684 MHz SQUID L1-3, f = 642 MHz SQUID K4-2, f = 702 MHz

Semiconductor TQL

Clarke and Kinion

quantum limit

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

SN1987A

CAST

ADMX Upgrade