Measuring the electron EDMwith Cold Molecules

E.A. Hinds

Warwick, 25 May, 2006

Imperial College London

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

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:

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?)

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)

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

~

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

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

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

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

| -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

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

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)

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

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

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

Measuring the edm

Applied magnetic field

Det

ecto

r co

un

t ra

te

E

B0

-E

= 4deET/

-B0

4deET/

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

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

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

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

The eEDM roadmap

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

Our alternating gradient decelerator design

high voltageelectrodes

21 stages

macor insulators

AG focussing in other contexts

Optical guiding

Ion Trapping

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)

Now also CaF

Vision of experiment with trapped molecules

supersonic sourcedecelerator

prepare split

trap ~ 1s

E

B

recombine probe

interferometer

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

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

CryoEDM starts in October

Several other neutron EDM experiments also starting

Ultimately 100x more sensitive

polarised neutrons moderated in superfluid helium

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

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

Rick Bethlem

Gerard Meijer

Antoine Weis

Collaborators

Mike Tarbutt Ben Sauer

Henry Ashworth

Ed Hinds

Richard Darnley

Jony Hudson

Manu Kerrinckx

Current Group Members