Search for the Electron
Electric Dipole Moment
Val Prasad
Yale University
Experiment:
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
D
look different after P
reversal
P
S
T
look different after T
reversal
T-violation: a window to new physics
CPT theorem  T-violation = CP-violation
Feynman Diagram

de
Ld    5 F
2
e
e
not renormalizable  loop diagrams
Theoretical Predictions for de
Yale I
(projected)
Berkeley
Yale II
(projected)
HsF
NAIVE SUSY
A-CP
AC
A-Un
M-H
SO(10) GUT
LR-S
Align
E-Un
TC
L-FC
10-26
Std Model
10-30
10-28
10-32
10-40
de (e·cm)
Experimental limit:
|de| < 1.610-27 ecm (Berkeley)
Std Model: Standard Model
LR-S: Left-Right Symmetric
L-FC: Lepton flavor-changing
M-H: Multi-Higgs
TC:
Technicolor
AC:
Accidental Cancellations
HsF:
A-CP:
A-Un:
Align:
E-Un:
Heavy sFermions
Approx. CP
Approx Universality
Alignment
Exact Universality
General Method to Detect an EDM

E
B
spin
 dE
  0 B 
   0 B 
 dE
Energy Shift ~ ____(de.Eeff)_______
Resolution
(Tcoh .√(dN/dt Tmeas))-1
Schiff’s theorem
Cannot apply an electric field to a free electron for long times
Use a neutral object (atoms, molecules)
 Ftotal  0  Felectric    Fmagnetic 
 Felectric    Fmagnetic 
  E v


r  c 
Near nucleus, v, E,  large + substantial amplitude for valence e-:
Fmag    B  ~  B
r ~ a0/Z;
v ~ Zc; E ~ Ze/r2; B ~ea0; (0) ~Z1/2
|<Eeff>|  Z32 (e/a02)  P
Molecules enhance electric fields
•
•
•
•
•
Atoms
O
E
Large laboratory fields
~50 kV/cm
E
~10
V/cm
ext
Leakage currents=BAD!!!
Pb
Smaller enhancement
10 V/cm
E
~10
int
factors
Molecules
Unpaired electron=free radical
Boltzmann distribution over many rovibrational states
M. G. Kozlov and D. DeMille
Phys. Rev. Lett. 89, 133001 (2002)
An aside: what’s an -doublet?

Non-rotating molecule
has internal
tensor Stark shift
  2
2
ESt  n  J e   
=0
Energy
 
n, E
 

J e  S ...  L 
=-1
=+1
-90
0
90
180
angle
to molecular
states
coupled
in 2nd axis
order
270
=1
via
molecular rotation (Coriolis)
Symmetric-antisymmmetric
2/E ~ 10-3E
Estates
~
(E
)

rot
split
by sttunnelingrot
Thallium vs PbO*
Atom/Molecule
Thallium
PbO*
Group
Berkeley
Yale/
Amherst
Applied field (V/cm)
105
>15
Effective field (V/cm)
6107
3-61010!!
Coherence time T (ms)
3
0.1
Count rate (1/s)
2109
1011
Figure of merit
1
240
Projected sensitivity (ecm)
210-28
10-29/10-31
Present limit (ecm)
<1.610-27
???
PbO*: ΔEedm = 2.5 x 1025 Hz x de (e-cm)
Excitation scheme
2+
2-
X(0)[1Σ+]
~12 MHz
a(1) [3 Σ+]
11+
2+
Laser pulse
λ~571 nm
t~10 ns
Bandwidth~1GHz~ΔνDoppler
R0 208Pb
J’’=0→J’=1
1~10 GHz
0+
intensity
Integrated
Signal (mV)
Molecular Spectra
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
20
18
16
14
12
10
8
6
4
2
0
R6-208
R7-206
R0(J”=0J’=1-)
208Pb
Tune laser here
0
10
20
30
40
50
Laser Frequency Detuning (GHz)
60
70
Omega Doublet
|e | f 
2
|f 
ν~11.2 MHz
νZeeman~300 kHz
|e 
m=-1
m=0
|e  | f 
2
m=1
 Stark ~ 20  60MHz
B =0
E =0
Excitation Scheme
RF pulse
1
0.8
B
0.6
0.4
0.2
-2
-1
1
2
   0 B  dE
E
Excitation Scheme
RF pulse
1
0.8
B
0.6
0.4
  0 B  dE
0.2
-2
-1
1
2
E
Excitation Scheme
1
0.8
  0 B  dE
0.6
0.4
B
0.2
-2
-1
1
2
RF pulse
E
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)
y
x
Present Experimental Setup
Photomultiplier tube
B
Solid quartz
light pipes
Vacuum chamber
Data
Processing
integral
Signal
PbO vapor Cell
Fourier
Transform
Frequency
•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
Quartz Oven
PbO Vapor Cell
•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
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
Magnetic Shield
Peripherals
To EDM
Experiment
Winston Cone
Quartz Oven Parts
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
EDM Measurement in PbO*
New mechanisms for suppressing systematics!
Brf
B
E
Brf
B
E
E reversal
Ћ  rf ΔEstark
Frequency for
de≠0
rf tuning adds NEW
reversal to the EDM
measurement
Frequency for
de=0
Ћ  rf ΔEstark
+ ΔE
-doublet
Brf
B
E
Brf
B
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
E
g-factor measurement
To what extent is the - doublet a perfect mirror image?
 
H B  gB  S
J  : g   1.860  0.008 and
g g   g 
g

 0.002 (
 0 ideal)
g
g
g
J  : g   1.857  0.008

-doublet useful as
Co-Magnetometer
Results help constrain calculation of enhancement-factor
Typical Data
160
Signal (mV)
150
Data
140
Fit
130
120
110
100
90
80
0
20
40
60
time after laser pulse (s)
80
Averaged over 0.5 s, Bz~60 mG
100
Rabi Flopping
56 RF cycles
beat frequency change (MHz)
1.E-03
8.E-04
6.E-04
4.E-04
2.E-04
0.E+00
1.1E+07
1.1E+07
1.1E+07
1.1E+07
1.1E+07
-2.E-04
-4.E-04
RF frequency (Hz)
1.2E+07
1.2E+07
Stark Shift = Zeeman Shift
Omega Doublet
|e | f 
2
|f 
ν~11.2 MHz
νZeeman~300 kHz
|e 
m=-1
m=0
|e  | f 
2
m=1
 Stark ~ 20  60MHz
B =0
E =0
Current Sensitivity
Current sensitivity to quantum beat frequency
1X10-27e.cm corresponds to beat frequency shift 10-25mHz
Straightforward modification to improve sensitivity to 100mHz / Hz
Two photodiodes with high quantum efficiency instead of single PMT
Excite from X(0)(v”=0) instead of X(0)(v”=1)
Use broader band interference filters
Use 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
100mHz
1

 20mHz
Average for T=25s  v 
Hz
T
1X10-29e·cm corresponds to 100-240μHz  T < 106s
Two orders of magnitude improvement on de in ~10days
The necessary modifications are now underway
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 …………….
Current Operating Condition
Density determined by collisional quenching
Adjust PbO density so excited state decay rate ~collisional quenching rate
1/ a(1) ~σnv, where a(1) ~ 80 μs
Measured σ~10-14cm2 n=3x1013cm-3 P=0.3mTorr T=690oC v=3x104cm/s
Minimum cell size determined by wall quenching
vx
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 section
Number of molecules excited/pulse(100Hz) ~1010
Number of photoelectrons detected /excited molecule ~ fewx10 -5
Total fluorescence rate ~ 107/sec
Background from blackbody radiation comparable to fluorescence
S contrast  fluorescence
~
~ 200 / s
N
background