Electron EDM search with PbO

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

3. The problem(s) with polar molecules:  Molecules with electron spin are thermodynamically disfavored (free radicals)  high temperature chemistry, even smaller signals  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) a(1) has very small -doublet splitting complete polarization with very small fields (~10 V/cm), equivalent to E  107 V/cm on an atom!  can work in vapor cell (MUCH larger density and volume than beam) PbO Cell: Tl Beam: N = nV ~ 1016 N = nV ~ 108

4. Amplifying the electric field Ewith a polar molecule Eext Pb+ Complete polarization of PbO* achieved with Eext ~ 10 V/cm Eint O– Inside molecule, electron feels internal field Eint ~ 2Z3 e/a022.1(b) - 4.0(a) 1010 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).

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

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

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

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

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

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

11. [D. Kawall et al., PRL 92, 133007 (2004)] 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: geff/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

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

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

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

15. S/N enhancements—far less than anticipated Bottom line: only ~2x improvement over Tl expected with current setup  --taking data soon

16. C’ Excite: X→a→C’ ( = 548 +1114 nm) Detect: C’→a ( = 380-450 nm) a arbitrary units X 10 20 30 40 50 60 70 • Dramatic reduction of blackbody, laser scatter • ~8x contrast • ~2x quantum eff. a Laser double-resonance detection Excite: X→a ( = 548 nm) Detect: X→a ( = 570 nm) arbitrary units X 10 20 30 40 50 60 70 s m

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

18.  A • Dominant noise from thermal  carrier: cancellation via “bridge” (= dark fringe interferometer) • Shot noise limit with ~1015 wave /shot looks feasible • Enhanced absorption with resonant cavity: S/N Q 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

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

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

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 2nd generation experiment based on long cell + microwave absorption underway • Projected 2nd 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)