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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…)