Measuring the electron EDM
with Cold Molecules
E.A. Hinds
Imperial College London
Warwick, 25 May, 2006
How the electron gets structure
point electron
+
+
-
+
+
polarisable vacuum with increasingly
rich structure at shorter distances:
(anti)leptons, (anti)quarks, Higgs (standard model)
beyond that: supersymmetric particles ………?
Electric dipole moment (EDM)
electron
spin
beyond std model:
edm
+
-
T
+
-
If the electron has an EDM,
nature has chosen one of these,
breaking T symmetry.
Two motivations to measure EDM
EDM is effectively zero in standard model
but
big enough to measure in non-standard models
direct test of physics beyond the standard model
(Q: is there a unified theory of all particle interactions?)
EDM violates T symmetry
Deeply connected to CP violation and the
matter-antimatter asymmetry of the universe
(Q: why is there more matter than antimatter?)
eEDM (e.cm)
10-22
10-24
10-26
10-28
Multi
Higgs
MSSM
f~1
Left MSSM
Right
f ~ a/p
10-30
10-32
10-34
10-36
Standard Model
Excluded region
(Tl atomic beam)
Commins (2002)
de < 1.6 x 10-27 e.cm
Our experiment
(YbF molecules)
is starting
to explore this region
CP from particles to atoms (main connections)
field theory
CP model
electron/quark
level
nucleon
level
nuclear
level
Tl, YbF
de
Higgs
SUSY
Left/Right
dq
atom/molecule
level
neutron
dcq
Strong
CP
~
qGG
NNNN
Schiff
moment
mercury
Theoretical consequences of electron EDM
de < 1.6 x 10-27 e.cm
- a direct window onto new physics
selectron
e
gaugino
g
e
naturally ~ a/p
CP phase from soft breaking
naturally O(1)
me
de ~ (loop)  2 sin CP
L
scale of SUSY breaking naturally ~200 GeV
SUSY electron edm
~ 5  1025 cm naturally
The “natural” SUSY EDM is too big by 300
CP < 310-3 ??
L > 4 TeV ??
The magnetic moment problem
Suppose de = 5 x 10-28 e.cm (just below current limit)
In a field of 100kV/cm
de.E ~_ 10-8 Hz
When does mB.B equal this ?
B ~_ 10-18 T !
It seems impossible to control B at this level
especially when applying a large E field
A clever solution
For more details, see E. A. H.
Physica Scripta T70, 34 (1997)
amplification (Sandars)
E
de 
electric field
Interaction energy
-de E•
FP
atom or molecule
containing electron
Polarization
factor
Structure-dependent
relativistic factor
~ 10 (Z/80)3 GV/cm
18 GV/cm
Effective field E (GV/cm)
Our experiment uses a molecule – YbF
20
15
10
Amplification in YbF
5
0
0
10
20
30
Applied field E (kV/cm)
 EDM interaction energy is a million times larger (10-2 Hz)
 mHz energy now “only” requires pT stray field control
 Insensitive to B perpendicular to E (suppressed by 1010)
 Hence insensitive to motional B (vxE/c2=104 pT)
The lowest two levels of YbF X2S+ (N = 0,v = 0)
+deE
F=1
+
| -1 >
| +1 >
+
E
-deE
170 MHz
F=0
|0>
Goal: measure the splitting 2deE to ~1mHz
Interferometer to measure 2deE
| +1 
| -1 
|0
E |+1
Source
B
0 ?
0
Split
Pump
A-X Q(0) F=1
| -1
170 MHz p pulse
Recombine
170 MHz p pulse
Phase difference = 2 (m B + deE)T/h
Probe
A-X Q(0) F=1
How we make the YbF beam
A pulsed supersonic jet source
Yb Target
Pulsed
Valve
2% SF6 in
4 bar Ar
YAG laser
(25mJ, 10ns)
Skimmer
Pulsed
YbF beam
The YbF gas pulses are cold (3K),
but move rapidly (600 m/s)
The whole experiment
PMT
rf
recombine
rf split
Pulsed YbF
beam
Probe
A-X Q(0) F=1
Pump
A-X Q(0)
F=1
Fluorescence
| +1 
| -1 
Scanning
Scanning the
the B-field
rf-frequency
Time-of-flight profile
|0
rfTime
frequency
(MHz)
B of
(nT)
flight
(ms)
Interference signal (kpps)
Fit to YbF interferometer fringes
Phase difference = 2(mB+deE)T/h
40
30
20
10
0
-60
-30
0
30
Magnetic field B (nT)
60
fringe pattern versus time of flight
arrival
time (ms)
experimental data
2.7
narrower fringes
2.6
slower molecules
2.5
faster molecules
2.4
2.3
-200
-100
0
100
200
Magnetic field B (nT)
Measuring the edm
Detector count rate
-E
 4deET/h
E
df = 4deET/h
-B0 B0
Applied magnetic field
EDM data taken
de (10-25 e.cm)
100 hrs at 13 kV/cm
3
2
1
-1
-2
-3
3
2
1
-1
-2
-3
80 hrs at 20 kV/cm
EDM Data summary
 Each dataset has a statistical sensitivity to de of 7 x 10-28 e.cm
 No result yet - the experiment is incomplete
 In particular, measurements of systematic effects
Systematic tests
16 internal machine states – linear combinations flag
undesirable asymmetries 
 4 external machine states 
 Simultaneous measurement of magnetic fields inside the
machine 
 Simultaneous measurement of leakage currents 
 Measurements at low electric field in progress
 Battery runs etc, etc in progress
 Repeat using a control molecule in preparation
Upgrades in progress
Improvement
Factor
Comment
Normalization detector
1.5
Normalize shot-to-shot variations
Higher repetition rate
2
From 10Hz to 50Hz
2nd pump laser-beam
1.5
Access N=2 population
Rb-cell magnetometry
1
Higher sensitivity to magnetic fields
Fiber laser
1
Low maintenance, more stable/reliable
Simultaneous YbF/CaF
1
Better measurement technique
Sensitivity level: 2 x 10-28 e.cm
Decelerated molecules
10
Much longer coherence time
Sensitivity level: ~10-29 e.cm
Deceleration and trapping
 We are building a Stark decelerator
for YbF and CaF molecules
 Aim to bring molecules to rest and
load them into a trap
 Perform the edm experiment with
slow, trapped molecules:
coherence times > 100ms
The eEDM roadmap
Principle of deceleration
For a review see
arXiv:physics/0604020 Apr 2006
2.5
Energy B
0
(1,0)
2.5
5
(0,0)
7.5
10
12.5
0
5
10
Electric Field B
15
e
20
Our alternating gradient decelerator design
21 stages
macor insulators
high voltage
electrodes
AG focussing in other contexts
Optical guiding
Ion Trapping
First YbF decelerator result
Decelerator off
Signal
Decelerator on
1.3
1.4
1.5
1.6
Time of flight (ms)
Phys. Rev. Lett. 92, 173002 (2004)
1.7
1.8
Now also CaF
Vision of experiment with trapped molecules
trap
t ~ 1s
supersonic source
E
B
decelerator
prepare split recombine probe
interferometer
Other electron EDM searches
Cs atoms
Fountain (LBL),
Trapped (Penn State), Trapped (Texas)
Long coherence time
Gadolinium Garnets
GGG (LANL), GIG (Amherst)
Huge number of electrons
Molecules
Metastable PbO in cell (Yale)
Large effective E field
Trapped PbF (Oklahoma)
Large effective E field
& long coherence time
Trapped HBr+ ions (JILA)
Neutron EDM expt
Room-temperature experiment finished
polarised neutrons
in a bottle
Hg atom co-magnetometer
laser beam
Measurement:
dnxE spin precession
New limit:
3.0 x 10-26 e. cm
hep-ex/0602020
Electric field 10kV/cm
CryoEDM starts in October
Ultimately 100x
more sensitive
polarised neutrons
moderated in
superfluid helium
Several other neutron EDM experiments also starting
Current status of EDMs
d(muon)  7×10-19
neutron:
electron:
d e.cm
10-20
Electromagnetic
10-22
d(proton)  6×10-23
YbF expt
10-24
Multi
Higgs
10-28
10-29
d(neutron)  3×10-26
SUSY
f~1
Left-Right
d(electron)  1.6×10-27
f ~ a/p
1960 1970 1980 1990 2000 2010 2020 2030
trapped
molecules
Conclusion
Measuring the electron EDM has
great potential to elucidate
•
particle physics beyond the standard model
•
CP violation
•
matter/antimatter asymmetry of the universe
Some of the
most fundamental questions in physics
Current Group Members
Collaborators
Richard Darnley Henry Ashworth Manu Kerrinckx
Jony Hudson Mike Tarbutt
Ben Sauer
Ed Hinds
Rick Bethlem
Gerard Meijer
Antoine Weis