Search for the Electron Electric Dipole Moment

Val Prasad

Yale UniversityExperiment:

D.DeMille, D. Kawall, R.Paolino, V. Prasad

F. Bay, S. Bickman, P.Hamilton,

Y. Jiang, Y.Gurevich

Yale University 

L.R.Hunter (Amherst)

Theory:

M. Kozlov (PNPI, St. Petersburg),

D. DeMille

An EDM Violates Parity and Time Reversal Symmetries and may provide evidence of

new physics

T-violation: a window to new physics

P T

D S

look different after P reversal

look different after T reversal

CPT theorem T-violation = CP-violation

Feynman Diagram

ee

2

5 Fde

d L

not renormalizable loop diagrams

Std Model: Standard ModelLR-S: Left-Right SymmetricL-FC: Lepton flavor-changingM-H: Multi-HiggsTC: TechnicolorAC: Accidental Cancellations

HsF: Heavy sFermionsA-CP: Approx. CPA-Un: Approx UniversalityAlign: AlignmentE-Un: Exact Universality

M-H

NAIVE SUSY

AC A-CP

A-Un

Align

HsF

SO(10) GUT

LR-S

L-FC

TC

10-26 10-28 10-30

de (e·cm)

Berkeley Yale I (projected)

10-32

E-Un

10-40

Std Model

Experimental limit: |de| < 1.610-27 ecm (Berkeley)

Yale II (projected)

Theoretical Predictions for de

General Method to Detect an EDM

dEB 0

dEB 0

dEB 0

spin

E

B dEB 0

Energy ShiftResolution

~ ____(de.Eeff)_______ (Tcoh .√(dN/dt Tmeas))-1

Schiff’s theorem

magneticelectric

magneticelectrictotal

FF

FFF 0

crBmagvE

BF ~

Near nucleus, v, E, large + substantial amplitude for valence e-:r ~ a0/Z; v ~ Zc; E ~ Ze/r2; B ~ea0; (0) ~Z1/2

|<Eeff>| Z32 (e/a02) P

Cannot apply an electric field to a free electron for long times

Use a neutral object (atoms, molecules)

Molecules enhance electric fields

Atoms• Large laboratory fields ~50

kV/cm• Leakage currents=BAD!!!• Smaller enhancement

factors

Pb

OE

Eext~10 V/cm

Eint~1010 V/cmMolecules

• Unpaired electron=free radical

• Boltzmann distribution over many rovibrational states

M. G. Kozlov and D. DeMillePhys. Rev. Lett. 89, 133001 (2002)

An aside: what’s an -doublet?

-90 0 90 180 270angle to molecular axis

En

erg

y

Symmetric-antisymmmetric states split by tunneling

=0

=-1=+1

=1 states coupled in 2nd order viamolecular rotation (Coriolis)E ~ (Erot)2/Est ~ 10-3Erot

LSJe

...

En

,

Non-rotating moleculehas internal

tensor Stark shift

22 eSt JnE

Thallium vs PbO*Atom/Molecule Thallium PbO*

Group Berkeley Yale/Amherst

Applied field (V/cm) 105 >15

Effective field (V/cm) 6107 3-61010!!

Coherence time T (ms) 3 0.1

Count rate (1/s) 2109 1011

Figure of merit 1 240

Projected sensitivity (ecm) 210-28 10-29/10-31

Present limit (ecm) <1.610-27 ???

PbO*: ΔEedm = 2.5 x 1025 Hz x de (e-cm)

Excitation scheme

0+

1-

2+

X(0)[1Σ+]

1-

1+

2+

2-

a(1) [3 Σ+]

~10 GHz

~12 MHz

Laser pulseλ~571 nmt~10 nsBandwidth~1GHz~ΔνDoppler

R0 208PbJ’’=0→J’=1

Molecular Spectra

R0(J”=0J’=1-)208Pb

X(v’’ = 1) a(v’ = 5) excitation ( = 571 nm)a(v’ = 5) X(v’’ = 0) detection ( = 548 nm)

Integrated over ~200 s after each pulse

Tune laser here

Inte

gra

ted

in

ten

sit

y

Omega Doublet

e|

f|

2

|| fe

m=-1 m=0 m=1

B =0 E =0

νZeeman~300 kHz

2

|| fe

ν~11.2 MHz

MHzStark 6020~

Excitation Scheme

B E

RF pulse

-2 -1 1 2

0.2

0.4

0.6

0.8

1

dEB 0

Excitation Scheme

B E

RF pulse

-2 -1 1 2

0.2

0.4

0.6

0.8

1

dEB 0

Excitation Scheme

B E

RF pulse

-2 -1 1 2

0.2

0.4

0.6

0.8

1

dEB 0

Quantum Beats• Coherent superposition of two states decaying to

the same state• Precession frequency proportional to energy

difference between states• Allows for Doppler free, very precise

spectroscopy (<1mHz)

x

y

Present Experimental Setup

Photomultiplier tube

Si gnal

Frequency

Solid quartz light pipes

DataProcessing

integral

Vacuum chamber

Fourier Transform

PbO vapor Cell

B

•A specialized oven to heat a novel vapor cell to temperatures of 700°C•The cell contains about 80cm3 of PbO vapor of natural isotopic abundance •Vacuum chamber surrounded by 3 orthogonal Helmholtz coils•Use Nd:YAG pumped dye laser at 570nm, 5-40 mJ /pulse, 1 GHz linewidth•Excite X(0)a(1) transition and detect quantum beat fluorescence signal•Analyze beat frequency•Perform reversal of E field, B field or RF transition to measure dipole induced frequency shift

PbO Vapor Cell

Main electrode

Guard ring

Sapphire window

•Re-entrant electrodes for homogeneous E field•Flat windows to reduce scattered light and birefringence•Larger volume to reduce wall quenching

Quartz Oven•Can withstand repeated thermal cycling to 800°C•~1300 W of power used•Excellent Temperature stability •wide optical access•low-inductance heater for fast switching

Magnetic Shield

Winston Cone

Quartz Oven Parts

Peripherals To EDM Experiment

Systematics Considerations

• Motional Magnetic Fields

• Magnetic Noise

• Leakage Currents

• Multi-photon ionization

• E-field gradients

• Inhomogeneities in E-field

• Stray B-fields and E-fields

B EBrf

B EBrf

B EBrfB EBrf

Ћ rf ΔEstark

Ћ rf ΔEstark

+ ΔE -doublet

E reversal

Frequency for de=0

Frequency for de≠0

Dashed-line energy levels show Zeeman shifts. Dotted-line levels show the additional linear Stark shift which would arise from a non-zero EDM.

-doublet levels = comagnetometer: Most systematics cancel in comparison

rf tuning adds NEWreversal to the EDM measurement

EDM Measurement in PbO*New mechanisms for suppressing systematics!

g-factor measurement

Results help constrain calculation of enhancement-factor

008.0857.1 : and 0.0081.860 :

gJgJ

ideal) 0g

g ( 0.002

g

g

g

g

g -doublet useful as Co-Magnetometer

To what extent is the - doublet a perfect mirror image?

SBgH B

Typical Data

Averaged over 0.5 s, Bz~60 mG

Rabi Flopping56 RF cycles

-4.E-04

-2.E-04

0.E+00

2.E-04

4.E-04

6.E-04

8.E-04

1.E-03

1.1E+07 1.1E+07 1.1E+07 1.1E+07 1.1E+07 1.2E+07 1.2E+07

RF frequency (Hz)

beat

freq

uen

cy c

han

ge (

MH

z)

Stark Shift = Zeeman Shift

Omega Doublet

e|

f|

2

|| fe

m=-1 m=0 m=1

B =0 E =0

νZeeman~300 kHz

2

|| fe

ν~11.2 MHz

MHzStark 6020~

Current sensitivity to quantum beat frequency

1X10-27e.cm corresponds to beat frequency shift 10-25mHz

Straightforward modification to improve sensitivity to

Two photodiodes with high quantum efficiency instead of single PMTExcite from X(0)(v”=0) instead of X(0)(v”=1)Use broader band interference filtersUse isotopic enriched 208PbO…

Expect to increase the count rate by more than three orders of magnitude, and the contrast by more than a factor of two

Current Sensitivity

The necessary modifications are now underway

1X10-29e·cm corresponds to 100-240μHz T < 106s

Two orders of magnitude improvement on de in ~10days

Average for T=25s

100mHz / Hz

100mHz 120mHz

Hz Tv

Conclusions

• Many preliminary steps have been successfully demonstrated

• Improvements in excitation and detection efficiencies look promising

• Attacking a few remaining experimental issues before we take a first look at the data …………….

Density determined by collisional quenchingAdjust PbO density so excited state decay rate ~collisional quenching rate1/ a(1) ~σnv, where a(1) ~ 80 μsMeasured σ~10-14cm2 n=3x1013cm-3 P=0.3mTorr T=690oC v=3x104cm/s

Minimum cell size determined by wall quenchingv x a(1) < L L~5cm

Density and cell size determine number of molecules in usable rovibrational state

f~B/kBT~0.3cm-1/670cm-1 3x10-4

S/ N estimated from laser power, cross sectionNumber of molecules excited/pulse(100Hz) ~1010

Number of photoelectrons detected /excited molecule ~ fewx10-5

Total fluorescence rate ~ 107/secBackground from blackbody radiation comparable to fluorescence

Current Operating Condition

contrast fluorescence~ ~ 200 /

background

Ss

N