PowerPoint Presentation

ASK 2011

A Microwave Cavity AxionExperimentfor Korea

Karl van BibberNaval Postgraduate SchoolMonterey, CA

April 2011

1Q: What is the most important qualification for an axion hunter?A: The Gift of Immortality

Juan Ponce de Leon (1474-1521),Spanish explorer who came to Florida seeking the Fountain of Youth

(Maybe why Pierre never seems to change?)

Looking for the axion may keep us youthful, but in fact physicists are not truly T-invariant!

Seriously, this is taking too long. We need to broaden the community of talent, and we need to work together! What this talk will be aboutThis will be a nuts-and-bolts talk about the microwave cavity experiment.

What things are important, and what things are hard.

It will be oriented to understanding what has been accomplished so far, what are the challenges ahead, and what are the opportunities for an experiment here.

A very rough scope of cost and effort will be attempted.

3The Axion

4ma , gaii fa1 ga maAxion modelsAxion basics (What you learn for free)106104102100ma (eV)1016101410121081010ga (GeV1)Light cousin of 0: J= 0

aa fa7/6 ma > 1 eVa > 1Sn1987a pulse precludes NNNNa for ma~10(30) eVSn1987aHorizontal BranchStar limitHorizontal Branch Starspreclude ga > 1010 GeV1

G.G. Raffelt Stars as Laboratories for Fundamental Physics U. Chicago Press (1996)Good news Parameter space is boundedBad news All couplings are extraordinarily weak5Axion-photon mixing provides the key [P. Sikivie, PRL 51, 1415 (1983)]

Dark matter

Solar

LaboratoryCoherent mixing of axions and photons over large spatial regions of strong magnetic fields (a sea of virtual photons) compensates for the extraordinarily small value of gaSee Raffelt & Stodolsky for general treatment of axion-photon mixing PRD 37, 1237 (1988)

6The cosmological inventory is now well-delineatedBut we know neither what the dark energy or the dark matter is

A particle relic from the Big Bang is strongly implied for DMWIMPs ?Axions ?

P02552-ljr-u-0047Nature of axionic dark matter, and principle of the microwave cavity experiment [Pierre Sikivie, PRL 51, 1415 (1983)]

E/E ~ 1011Resonance condition:hn = mac2[ 1 + O(b2~ 10-6) ]

Signal power:P ( B2V Qcav )( g2 ma ra ) ~ 1023WLocal Milky Way density:halo ~ 450 MeV/cm3

Thus for ma ~ 10 eV:halo ~ 1014 cm3virial ~ 103 : De Broglie ~ 100 m

flow ~ 107 :Coherence ~ 1000 kmKey point ! The signal is the Total Energy ( = Mass + Kinetic )of the axion 8

Figure 2ADMX stood on the shoulders of giants

From W. Wuensch et al., Phys. Rev. D40 (1989) 3153We learned much from the first-generation expts (~ liter volume) Already came within a factor of 100-1000 of the desired sensitivityPRL 80 (1998) 2043PRD 64 (2001) 092003ApJ Lett 571 (2002) 27PRD 69 (2004) 011101(R)PRL 95 (9) 091304 (2005)PRD 74 (2006) 012006PRL 104 (2010) 041301+ 4 Ph.D. theses9Basic formulae

Signal power:Scanning rate:QL = Q0/(1+) Loaded Q-value; couplingf = f - f0 Offset from centralClmn Cavity form-factorf Cavity bandwidthfstepFrequency tuning stepsnOverlapping tuning stepsNote both the power and scanning rate depend linearly on QL10Rules-of-thumb for optimizing the experimentIdeally one wants sufficiently low temperature such that one can:Be sensitive to the most pessimistic model axion (e.g. DFSZ ) Which only occupies a fraction of the halo density (e.g. 10% )Finish the whole works in a tractable time (e.g.10 yrs )For scanning at a fixed sweep rate

For scanning at a fixed coupling ga11

Microwave cavity basics (I)

Required/desired features: Cover ~100 MHz to ~100 GHz Practical tuning, 50% High quality factor, Q ~ 105 High cavity form-factor, C = O(1) Minimal mode-crossings Minimal mode-localizationSimplest right circular cavity, TM010: Ez = J0(kr) (empty) f0 = 0.115 GHz / R[m] C010 = 0.69 h = mc2 ma = 4.136 eV . f[GHz]12Microwave cavity basics (II)Cavity form-factor Clmn(overlap of E, Bext):For uniform B = B0: C(TM010) ~ 0.69 Much smaller for TM0n0 TE, TEM identically 0

Try to use the TM010-like mode for all configurations Cavity quality, Qlmn:

In high B-field, low-T: Must be copper (not SC!) Anomalous skin depth limitQ limited to few 105, but we reach the theoretical max13

Microwave cavity basics (III) TuningTuning rods, radial offsetEz for TM010 mode; two metal rods half-way from center Metal - up; dielectric - down Keep longitudinal symmetryMode-crossings Keep cavity aspect ratio L/R low But can walk-around crossings14

Real-life form-factors, Q vs. frequencyC010 vs. frequency, for cases of cavity filled with 1-torr He gas (solid); and SHe filled (dashed)QL vs. frequency for case of two copper rods 15dc SQUID basics

16

Quantum LimitGaAsSQUID amplifier design and performanceVaractor tuning of microstrip SQUID

30252015105Gain (dB)220200180160140120100Frequency (MHz)-1 V01346922 V2NoVaractor18Axion Dark Matter eXperiment (ADMX)University of California, BerkeleyJohn Clarke

University of FloridaJeffrey Hoskins, Junseek Hwang, Pierre Sikivie, Neil Sullivan, David Tanner

Lawrence Livermore National LaboratoryStephen Asztalos, Gianpaolo Carosi, Christian Hagmann, Darin Kinion, Karl van Bibber

National Radio Astronomical ObservatoryRichard Bradley

University of WashingtonMichael Hotz, Leslie Rosenberg, Gray Rybka, Andrew Wagner

19Axion hardware

ADMX LLNL-UW-Florida-Berkeley-NRAO20Axion hardware (contd)

21ADMX is the worlds quietest spectral receiver: Sensitive to one RF photon every two weeksSystematics-limited for signals of 10-26 W 10-3 of DFSZ axion power.Last signal received from Pioneer 10 (6 billion miles away) ~ 10-21 W.

Dicke Radiometer equation:22Sample data and candidates

Signal maximizes in the wings, and furthermore is episodic Radio peakDistributed over many subspectra (good), but didnt repeat Statistical peak 23Brief outline of analysis 100 MHz of data

24Origin of the non-thermalized component

251-D infall, and the folding of phase space

26Velocity spectrum of axions at our solar system

27Diurnal and sidereal oscillation of the fine-structure

28Simulation of one infall modelDailyAnnual

29Diurnal and sidereal oscillation of late-infall axion peaks

Frequency1a1b2a2bTime (seconds) x 10-630Results of a high-resolution analysisPRL 95 (9) 091304 (2005)

2000 s52 s

Measured power in environmental (radio) peak same in Med- & Hi-Res 31 So far, no axion ! (over 1.9 - 3.6 meV)

Reduce System Temperature ADMX Phase II: add Dilution Refrigerator

Go up in Frequency ADMX-HF (High Frequency): smaller microwave cavities

,Need to push the experiment on two fronts:So where are we going in the future?Improve sensitivity & scan speed (reduce TS) ADMX Phase II

Go from Gen 2.5 to Gen 3.0

Increase mass reach (increase frequency ) ADMX-HF

Franchise Model for ADMX, One experiment, two sites

Allows us to attack two decades of mass in parallel, rather than serially !

More later

ADMX Phase II will be both more sensitive and faster for low massesADMX-HF at Yale will be a very small experiment !

Design of cavity & magnetDilution refrigerator above & below deckADMX-HF will also be a test-bed for innovative concepts, e.g. thin-film superconducting cavitiesADMX Phase II & ADMX-HF Coverage36

Wa ~ 0.23ADMX - HFKVSZDFSZADMX(complete)ADMX(Phase II)ADMX(Higher TM)110100ma (meV)f (GHz)0.51 25102010-1210-1310-1410-1510-16gagg [GeV-1]

1 GHz10 GHz100 GHzFor the long term, ADMX needs concurrent R&D To get to 10 GHz (40 eV), and ultimately 100 GHz (0.4 meV), we need to:

Develop new RF cavity geometries Develop new SQUID geometries

37Atoms with a single electron promoted to a large principal quantum number, n >> 1. Superposition of Rydberg states yields classical atoms with macroscopic dimensions (e.g. ~ 1 mm).

Potential for highly sensitive microwave photon detectors (RF photo-multiplier tubes) realized by Kleppner and others in the 1970s. The axion experiment is an ideal application for Rydberg atoms:Rydberg-atom single-quantum detectorsMost importantly, being a phaseless detector (photons-as-particles), the Rydberg-atom detector can evade the standard quantum limit:h = kT

Large transition dipole moments

Long liftetimes

Transitions span microwave range

38

Fraction 85Rb 111s1/2 111p3/2 Rydberg single-quantum detection (S. Matsuki et al., Kyoto)

The blackbody spectrum has been measured at 2527 MHz a factor of ~2 below the standard quantum limit (~120mK)M. Tada et al., Phys. Lett. A (accepted)39There is one more thing we need to do to complete the strategyWe also need to go down in frequency !

One concrete motivation string theory predicts many axions, but generally much lower in mass, ma ~ neV (Witten, Srvcek; Kim)

More generally, we cannot really say where the axion is, and must be prepared to look everywhere in m , g

Searching in the ma < 1 meV range could be a great opportunity for the Korea Axion CenterHow would one go about this?Axion electrodynamics (Sikivie, 1983)

Our familiar realization of axion electrodynamics:Case of large fa/N , and magnetic diameter D