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. DeMilleYale Physics Department University

Funding: NSF, Packard Found., CRDF, NIST, Sloan, Research Corp.

General method to detect an EDM

Energy level picture:

Figure of merit: int1 1

/coh

coh

shift dEE C N T

resolution S N

E+2dE

+2dE

B

E-2dE

-2dE

S

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 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

Amplifying the electric field with a polar molecule

int

Pb+

O–

ext

Inside molecule, electron feels internal field

int ~ 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).

Complete polarization

of PbO* achieved with

ext ~ 10 V/cm

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

Brf z

BJ=1-

J=1+

+

- +

-+

+

- +

-

-a(1) [3+]

EDM measurement in PbO*

“Internalco-magnetometer”:most systematics

cancel in comparison

+

-n

+

-

n

+

-n

+

-

n

B EEEE

Novel state structure

allows extra reversal of EDM signal

Proof-of-principle setup (top view)

Pulsed Laser Beam5-40 mJ @ 100 Hz ~ 1 GHz B

Larmor Precession ~ 100 kHz

PMT

B

solid quartz lightpipes

DataProcessin

g

Vacuum chamber

E

quartz oven structure

Si g

nal

Frequency

PbO vapor cell

Vapor cell technology allows high count rate(but modest coherence time)

Laser-only spin preparation for proof of principle

m = 0m = -1 S m = +1 S

X, J=0+

|| x

J=1-

J=1+

a(1) [3+]

rotational substructure

570 nm

548 nm

vibrational substructure

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

Verification of co-magnetometer concept Zeeman splitting ~ 450 kHz

Zeeman splitting slightly different in lower level

~11 MHz RF E-fielddrives 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

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 measurementusing quantum beats in fluorescence

•g-factors of -doublet states match precisely: geff/g < 510-4

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)]

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 decayw/shaped audio freq. drive

State preparation: rotational Raman excitation

J=1

laser-preparedsuperposition, as in proof-of-principle(no good for EDM)

laser + wavepreparation,

as needed for EDM

J=2

40 MHz

28.2 GHz

28.2-.04 GHz

Doesn’t work!?!

Quasi-optical microwave delivery

Quartz lightpipes = multi-mode quasi-optical “fibers” for microwaves

Laser beam overlaps with microwave beam

“Dichroic” beamsplitterseparates

laser & microwave beams

PbO cell

S/N enhancements—far less than anticipated

Change Expected Actual Comments

Pure 208PbO 2x S, 2x C 2x S, 1x C??

Contrast not understood

Laser power 6x S ~3x S Ageing laser

2nd detector 2x S 2x S (est.) Trivial?

Broad interference filter

20x S ~5x S (est.) Too much laser scatter, blackbody

Vibrational levelv”=0 vs. v”=1

3x S1.3x C

1x S1x C

Too much laser scatter, blackbody

Solid state detector(photodiode/APD)

6x S 1x Too much laser scatter, signals too small

Bottom line: only ~2x improvement over Tl expected with current setup --taking data soon

Laser double-resonance detection

Excite: X→a ( = 548 nm)Detect: X→a ( = 570 nm)

X

aar

bitr

ary

units

70605040302010s

X

a

C’

Excite: X→a→C’ ( = 548 +1114 nm)Detect: C’→a ( = 380-450 nm)

arbi

trar

y un

its

70605040302010

•~8x contrast•~2x quantum eff.

•Dramatic reduction of blackbody, laser scatter

A sad story: double-resonance detectionDOESN’T WORK!*&%!

a

C’

phasedifference

eit

TransitionProbability

|—>|+>

|+>|—>

|—>+|+>/2|—>-|+>/2

1+cos(t)

1+cos(t) [+]+

1-cos(t) [-]=1!!!

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 ~1015 wave /shot looks feasible

A

Schematic of planned absorption detection scheme

“bridge”

Magic tee

Magic tee

Mixer/ detector

lens

horn

lens

cavity mirror

horncavity mirror

~15 cm diam.50 cm long

alumina tube cell

cos voltage onrod electrodes

for transverse E-field

•Long cell minimal effect of leakage currents, easier heating & shielding

Bottom line: de 10-29 ecm looks feasible!(50 cm long cell, Q = 100, shot-noise limited)

J=1

J=2

J=1

J=2

28.2 GHz

First detection of microwave absorption in PbO(using current setup, no optimization)

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 ecm (better estimate to come soon…)

The PbO EDM groupPostdocs:

(David Kawall)(Val Prasad)

Grad students:(Frederik Bay)

Sarah BickmanYong Jiang

Paul Hamilton

Undergrads:Robert Horne

Gabriel Billings

Collaborators:Rich Paolino

(USCGA)David Kawall

(UMass)