measuring the electron edm with cold molecules e.a. hinds warwick, 25 may, 2006 imperial college...
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Measuring the electron EDMwith Cold Molecules
E.A. Hinds
Warwick, 25 May, 2006
Imperial College London
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polarisable vacuum with increasinglyrich structure at shorter distances:
+ +
++
(anti)leptons, (anti)quarks, Higgs (standard model)beyond that: supersymmetric particles ………?
How the electron gets structure
-
point electron
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electronspin
+-edm
Electric dipole moment (EDM)
T +-
If the electron has an EDM,nature has chosen one of these,
breaking T symmetry.
beyond std model:
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Two motivations to measure EDM
EDM is effectively zero in standard modelbut
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?)
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Left -Right
MSSM ~
Multi Higgs
MSSM
~ 1
10-24
10-22
10-26
10-28
10-30
10-32
10-34
10-36
eEDM (e.cm)
Our experiment (YbF molecules)
is startingto explore this region
Standard Model
de < 1.6 x 10-27 e.cm
Commins (2002)
Excluded region (Tl atomic beam)
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Tl, YbF
atom/moleculelevel
CP from particles to atoms (main connections)
nuclearlevel
NNNNSchiff
momentmercury
HiggsSUSY
Left/Right
StrongCP
field theoryCP model
GG
neutron
nucleonlevel
electron/quark level
de
dq
dcq
~
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Theoretical consequences of electron EDM
de < 1.6 x 10-27 e.cm - a direct window onto new physics
The “natural” SUSY EDM is too big by 300
CP < 310-3 ?? > 4 TeV ??
SUSY electron edm
e e
selectron
2mede ~ (loop) sin CP
gaugino
CP phase from soft breaking naturally O(1)
scale of SUSY breaking naturally ~200 GeV
naturally ~
~ 5 1025 cm naturally
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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 B.B equal this ?
B _ 10-18 T !~
It seems impossible to control B at this levelespecially when applying a large E field
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A clever solution
E
electric field
de
amplification
atom or molecule containing electron
(Sandars)
For more details, see E. A. H. Physica Scripta T70, 34 (1997)
Interaction energy
-de E•
F PPolarization factor
Structure-dependent
relativistic factor ~ 10 (Z/80)3 GV/cm
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Our experiment uses a molecule – YbF
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)
0
5
10
15
20
0 10 20 30
Applied field E (kV/cm)
Eff
ecti
ve f
ield
E
(G
V/c
m)
Amplification in YbF
18 GV/cm
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| -1 > | +1 >
| 0 >
The lowest two levels of YbF
Goal: measure the splitting 2deE to ~1mHz
F=1
F=0
E
-deE
+deE
+-
+-
X2+ (N = 0,v = 0)
170 MHz
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Interferometer to measure 2deE
PumpA-X Q(0) F=1
0
| -1 | +1
| 0
Split| -1
|+1
170 MHz pulseProbe
A-X Q(0) F=1
0 ?
Recombine170 MHz pulse
Phase difference = 2 ( B + deE)T/
E B
Source
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How we make the YbF beam
PulsedValve
Yb Target
YAG laser(25mJ, 10ns)
Skimmer
2% SF6 in4 bar Ar
PulsedYbF beam
A pulsed supersonic jet source
The YbF gas pulses are cold (3K),
but move rapidly (600 m/s)
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The whole experiment
Pulsed YbF beam
PumpA-X Q(0) F=1
ProbeA-X Q(0) F=1
PMT
rf split
rfrecombin
e
Flu
ores
cenc
e
Time of flight (s)
Time-of-flight profile
rf frequency (MHz)
Scanning the rf-frequency Scanning the B-field
B (nT)
| -1 | +1
| 0
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Fit to YbF interferometer fringesIn
terf
ere
nce
sig
nal (k
pp
s)
Magnetic field B (nT)
Phase difference = 2(B+deE)T/
-60 -30 0 30 60
40
30
20
10
0
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2.7
2.6
2.5
2.4
2.3
-200 0-100 100 200
Magnetic field B (nT)
experimental data
arrivaltime (ms)
fringe pattern versus time of flight
slower molecules
faster molecules
narrower fringes
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Measuring the edm
Applied magnetic field
Det
ecto
r co
un
t ra
te
E
B0
-E
= 4deET/
-B0
4deET/
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100 hrs at 13 kV/cm
80 hrs at 20 kV/cm3
2
1
-1
-2
-3
EDM data taken
de (10-25 e.cm)
3
2
1
-1
-2
-3
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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
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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
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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
Upgrades in progress
Decelerated molecules 10 Much longer coherence time
Sensitivity level: ~10-29 e.cm
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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
Deceleration and trapping
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The eEDM roadmap
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Principle of deceleration
0 5 10 15 20Electric FieldBe
12.5
10
7.5
5
2.5
0
2.5
ygrenEB
(0,0)
(1,0)
For a review seearXiv:physics/0604020 Apr 2006
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Our alternating gradient decelerator design
high voltageelectrodes
21 stages
macor insulators
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AG focussing in other contexts
Optical guiding
Ion Trapping
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1.3 1.4 1.5 1.6 1.7 1.8
Time of flight (ms)
Sig
nal
Decelerator off
Decelerator on
First YbF decelerator result
Phys. Rev. Lett. 92, 173002 (2004)
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Now also CaF
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Vision of experiment with trapped molecules
supersonic sourcedecelerator
prepare split
trap ~ 1s
E
B
recombine probe
interferometer
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Other electron EDM searches
Cs atomsFountain (LBL), Trapped (Penn State), Trapped (Texas)
Long coherence time
GGG (LANL), GIG (Amherst)
Gadolinium GarnetsHuge number of electrons
MoleculesMetastable PbO in cell (Yale) Large effective E field
Trapped PbF (Oklahoma)
Trapped HBr+ ions (JILA)Large effective E field& long coherence time
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Neutron EDM expt
Room-temperature experiment finished
Measurement: dnxE spin precession
polarised neutrons in a bottle
Hg atom co-magnetometer laser beam
New limit: 3.0 x 10-26 e. cm
hep-ex/0602020
Electric field 10kV/cm
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CryoEDM starts in October
Several other neutron EDM experiments also starting
Ultimately 100x more sensitive
polarised neutrons moderated in superfluid helium
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d(muon) 7×10-19
Left-Right
10-20
10-22
10-24
d e.cm
MultiHiggs SUSY
Electro-magnetic
neutron:
electron:
1960 1970 1980 1990 2000 2010 2020 2030
10-28
10-29
Current status of EDMs
d(neutron) 3×10-26
d(proton) 6×10-23YbF expt
trappedmolecules
d(electron) 1.6×10-27
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Conclusion
Measuring the electron EDM has
great potential to elucidate
• particle physics beyond the standard model
• matter/antimatter asymmetry of the universe
• CP violation
Some of themost fundamental questions in physics
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Rick Bethlem
Gerard Meijer
Antoine Weis
Collaborators
Mike Tarbutt Ben Sauer
Henry Ashworth
Ed Hinds
Richard Darnley
Jony Hudson
Manu Kerrinckx
Current Group Members