1. Electron EDM search with PbO  review: basic ideas, previous results  work towards EDM data  current status: reduction in anticipated sensitivity  a new approach, thwarted  hope for the future…. D. DeMille Yale Physics Department University Funding: NSF, Packard Found., CRDF, NIST, Sloan, Research Corp.

2. General method to detect an EDM Energy level picture: Figure of merit: E +2dE B  E -2dE S 

3. The problem(s) with polar molecules:  Diluted signals due to thermal distribution over rotational levels (~10 -4 ) Addressing the problems with metastable PbO a(1)[ 3  + ]  PbO is thermodynamically stable (routinely purchased and vaporized) a(1) populated via laser excitation (replaces chemistry)  Molecules with electron spin are thermodynamically disfavored (free radicals)  high temperature chemistry, even smaller signals  a(1) has very small  -doublet splitting  complete polarization with very small fields (~10 V/cm), equivalent to E  10 7 V/cm on an atom!  can work in vapor cell (MUCH larger density and volume than beam) PbO Cell:Tl Beam: N = nV ~ 10 16 N = nV ~ 10 8

4. Amplifying the electric field E with a polar molecule E int Pb + O–O– E ext Inside molecule, electron feels internal field E int ~  2 Z 3 e/a 0 2  2.1 (b) - 4.0 (a)  10 10 V/cm in PbO* (a) Semiempirical: M. Kozlov & D.D., PRL 89, 133001 (2002); (b) Ab initio: Petrov, Titov, Isaev, Mosyagin, D.D., PRA 72, 022505 (2005). Complete polarization of PbO* achieved with E ext ~ 10 V/cm

5. Spin alignment & molecular polarization in PbO (no EDM) m = 0 E + - n + - n + - n + - n m = -1 S m = +1 S X, J=0 +  || z S B rf  z B J=1 - J=1 + + - + - + + - + - - a(1) [ 3  + ]

6. EDM measurement in PbO* “Internal co-magnetometer”: most systematics cancel in comparison + - n + - n + - n + - n B E E E E Novel state structure allows extra reversal of EDM signal

7. Proof-of-principle setup (top view) Pulsed Laser Beam 5-40 mJ @ 100 Hz  ~ 1 GHz   B Larmor Precession ~ 100 kHz PMT B solid quartz light pipes Data Processing Vacuum chamber E quartz oven structure PbO vapor cell Vapor cell technology allows high count rate (but modest coherence time)

8. Laser-only spin preparation for proof of principle m = 0 m = -1 S m = +1 S X, J=0 +  || x J=1 - J=1 + a(1) [ 3  + ] rotational substructure 570 nm 548 nm vibrational substructure

9. Zeeman quantum beats in PbO: g-factors Problems with fluorescence quantum beats: Poor contrast C~10% Backgrounds from blackbody, laser scatter  reduced collection Poor quantum efficiency for red wavelengths Gives info on: Density limits S/N in frequency extraction g-factors E-field effects

10. Verification of co-magnetometer concept Zeeman splitting ~ 450 kHz Zeeman splitting slightly different in lower level ~11 MHz RF E-field drives transitions ~1.6 ppt shift in Zeeman beat freq. g/g = 1.6(4) 10 -3  -doublet will be near-ideal co-magnetometer Also:   = 11.214(5) MHz; observed low-field DC Stark shift

11. Status in 2004: a proof of principle PbO vapor cell technology in place Collisional cross-sections as expected  anticipated density OK Signal size, background, contrast: Many improvements needed to reach target count rate & contrast Shot-noise limited frequency measurement using quantum beats in fluorescence g-factors of  -doublet states match precisely:  g eff /g < 5  10 -4  systematics rejection from state comparison very effective E-fields OK: no apparent problems EDM state preparation not demonstrated EDM-generation cell & oven needed [D. Kawall et al., PRL 92, 133007 (2004)]

12. Sapphire windows bonded to ceramic frame with gold foil “glue” Gold foil electrodes and “feedthroughs” PbO vapor cell and oven Opaque quartz oven body: 800 C capability; wide optical access; non-inductive heater; fast eddy current decay w/shaped audio freq. drive

13. State preparation: rotational Raman excitation J=1 laser-prepared superposition, as in proof-of-principle (no good for EDM) laser + wave preparation, as needed for EDM J=2 40 MHz 28.2 GHz 28.2-.04 GHz Doesn’t work!?!

14. Quasi-optical microwave delivery Quartz lightpipes = multi-mode quasi-optical “fibers” for microwaves Laser beam overlaps with microwave beam “Dichroic” beamsplitter separates laser & microwave beams PbO cell

15. S/N enhancements—far less than anticipated ChangeExpectedActualComments Pure 208 PbO2x S, 2x C2x S, 1x C?? Contrast not understood Laser power6x S~3x SAgeing laser 2 nd detector2x S2x S (est.)Trivial? Broad interference filter 20x S~5x S (est.)Too much laser scatter, blackbody Vibrational level v”=0 vs. v”=1 3x S 1.3x C 1x S 1x C Too much laser scatter, blackbody Solid state detector (photodiode/APD) 6x S1xToo much laser scatter, signals too small Bottom line: only ~2x improvement over Tl expected with current setup  --taking data soon

16. Laser double-resonance detection Excite: X→a ( = 548 nm) Detect: X→a ( = 570 nm) X a arbitrary units 70605040302010 m s ~8x contrast ~2x quantum eff. Dramatic reduction of blackbody, laser scatter

17. A sad story: double-resonance detection DOESN’T WORK!*&%! a C’ phase difference e i  t Transition Probability |—> |+> |—>|—> |—>+|+>/2 |—>-|+>/2 1+cos(  t) 1+cos(  t) [+] + 1-cos(  t) [-] =1!!!

18. Back to the future: absorption detection w/microwaves long cylindrical cell for increased absorption path  P/P ~ 10 -4 (cross-section & density well-known) P ~ 100 W in cell for no saturation Enhanced absorption with resonant cavity: S/N Q Dominant noise from thermal  carrier: cancellation via “bridge” (= dark fringe interferometer) Shot noise limit with ~10 15 wave /shot looks feasible  A

19. Schematic of planned absorption detection scheme “bridge” Magic tee Mixer/ detector lens horn lens cavity mirror horn cavity mirror ~15 cm diam. 50 cm long alumina tube cell cos voltage on rod electrodes for transverse E-field Long cell  minimal effect of leakage currents, easier heating & shielding Bottom line: d e  10 -29 ecm looks feasible! (50 cm long cell, Q = 100, shot-noise limited) J=1 J=2 28.2 GHz

20. J=1 J=2 28.2 GHz First detection of microwave absorption in PbO (using current setup, no optimization)

21. Status of electron EDM search in PbO Current version with fluorescence detection set to take data soon (~end of summer?) All major parts in place, but projected sensitivity (statistical) now only ~2x beyond current Tl result Major redesign for 2 nd generation experiment based on long cell + microwave absorption underway Projected 2 nd generation sensitivity well beyond 10 -29 e  cm (better estimate to come soon…)

22. The PbO EDM group Postdocs: (David Kawall) (Val Prasad) Grad students: (Frederik Bay) Sarah Bickman Yong Jiang Paul Hamilton Undergrads: Robert Horne Gabriel Billings Collaborators: Rich Paolino (USCGA) David Kawall (UMass)