Search for the electron’s EDM

E.A. Hinds

PCPV, Mahabaleshwar, 22 February 2013

Centre for Cold MatterImperial College London

Is the electron round?

+ +

++

polarisable vacuum with increasinglyrich structure at shorter distances:

(anti)leptons, (anti)quarks, Higgs (standard model)beyond that: supersymmetric particles ………?

How a point 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 . . . CP

Left -Right

otherSUSY

Multi Higgs

MSSM 10-24

10-22

10-26

10-28

10-30

10-32

10-34

10-36

eEDM (e.cm)

Standard Model 4

The interestingregion of sensitivity

Theoretical estimates of eEDM

Insufficient CPto make universe

of matter

e e

gselectron

electron

de

Suppose de = 5 x 10-28 e.cm(the region we explore)

In a field of 10kV/cm de E _ 1 nHz ~

This is very small

E

= 1 x 10-19 e.a0

When does mB.B equal this ?

B _ 1 fG~

The magnetic moment problem

5

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 Z3

6

Our experiment uses a polar molecule – YbF

EDM interaction energy is a million times larger (mHz)

needs “only” nG stray B field control

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

15 GV/cm

7

Pulsed YbF beam

Pumplaser

Probelaser

PMT

3K beamrf pulse

HV+

HV-

How it is donerf pulse

B

Measuring the edm

Applied magnetic field

Det

ecto

r co

un

t ra

te

B

-EE

Interferometer phase f = 2(mB + dehE)t/h-

de

-B

9

Modulate everything

• Generalisation of phase-sensitive

detection

• Measure all 512 correlations.

• E·B correlation gives EDM signal

±E±B

±B

±rf2f±rf1f

±rf2a±rf1a

±laser f±rf

spin interferometer signal

9 switches:

512 possible correlations

10

** Don’t look at the mean edm **

• We don’t know what result to expect.

• Still, to avoid inadvertent bias we hide the mean edm.

• An offset is added that only the computer knows.

• More important than you might think.– e.g. Jeng, Am. J. Phys. 74 (7), 2006. 11

2011 Data:6194 measurements (~6 min each) at 10 kV/cm.

bootstrap methoddeterminesprobability distribution

12-5 50

Gaussiandistribution

Distribution ofedm/edm

2

1

0

-1

-2

EDM (10-25 e.cm)

25 million beam shots

Measuring the other 511 correlations

correlation mean s mean/sfringe slope calibrationbeam intensityf-switch changes rf amplitudeE drift

E asymmetry E asymmetryinexact π pulse

• The rest are zero (as they should be) !

13

• Only now remove blind from EDM

Current status

de = (-2.4 5.7 1.5) ×10-28 e.cm

68% statisticalsystematic - limited by statistical noise

de < 1 × 10-27 e.cm with 90% confidence

• Previous result - Tl atoms

de < 1.6 × 10-27 e.cm with 90% confidence

• 2011 result – YbF Hudson et al. (Nature 2011)

Regan et al. (PRL 2002)Dzuba/Flambaum (PRL 2009)Nataraj et al. (PRL 2011)

14

Kara et al. NJP 14, 103051 (2012)

Left -Right other

SUSY

Multi Higgs

MSSM 10-24

10-22

10-26

10-28

10-30

10-32

10-34

10-36

eEDM (e.cm)

We are starting toexplore this region

Standard Model

de < 1 x 10-27 e.cm

New excluded region

15

How we will improvePhase 1 Small upgrades: 3 x improvement

– in progress

Phase 2 Cryogenic source of YbF – almost ready

Phase 3 Laser-cooled molecular fountain – being developed

16

Phase 1:

Now making a210-28 e.cm

EDM measurement

• Longer interferometer• Lower background

2.5sensitivity

6543210

Stray Bx

E direction

E magnitude

Stray By

Pump pol.

Probe pol.

Pump freq

Probe freq

F=1 detect

Max uncertainty (10-29 e.cm)

Systematics emphasised total < 10-28 e.cm

Defects emphasised

Phase 2 - cryogenic buffer gas source of YbF

YbF beam

YAGablationlaser

3K He gas cell

Yb+AlF3

target

18

Cryogenic beam spectrum

Rotational temperature: 4 ± 1 K Translational temperature: 5 ± 1 K

19

10 more molecules/pulse

=> 10 better EDM signal:noise ratio4 longer interaction time (slower beam)

=> access to mid 10-29 e.cm range

3K beamsource

laser cooling

1/2 sec flight time (instead of 1/2 ms)

Phase 3 – a molecular fountain

Laser cooling

=> 610-31 e.cm statistical (in 8 hrs)

detectionguide

HV+ HV-

He

rf pulse

20Tarbutt et al. arXiv:1302.2870

Other eEDM experiments in preparation

WC : 3Δ1 ground stateLeanhardt group, Michigan

Acme collaboration, Harvard/Yale

ThO : 3Δ1 metastable

HfF+ : 3Δ1 ground stateCornel Group JILA

Atom experiments in preparationCs in optical lattice: Weiss group, Penn State (next year?)

Heinzen group, Texas (2 years?)

Fr in a MOT: Tohoku/Osaka (starting 2014)

d(muon) < 1.9×10-19

10-20

10-22

10-24

d e.cm

1960 1970 1980 1990 2000 2010 2020 2030

Current status of EDMs

d(proton) < 5×10-24

d(electron) < 1×10-27

neutron:

Left-Right

MSSM

Multi

Higgs

electron:

10-28

10-29

d(neutron) < 3×10-2610-26

YbF

22

Summary

Atto-eV molecular spectroscopytells us about TeV particle physics:

specifically probes CP violation

(how come we’re here?)

23the electron is too round for MSSM!

e- EDM is a direct probe of physics beyond SM

Left -Right other

SUSY

Multi Higgs

MSSM 10-24

10-22

10-26

10-28

10-30

we see a way to reach <10-30

Thanks to my colleagues...

EDM measurement:Joe Smallman

Jack Devlin

Dhiren Kara

Buffer gas cooling:Sarah Skoff

Nick Bulleid

Rich Hendricks

Laser cooling:Thom Wall

Aki Matsushima

Valentina Zhelyazkova

Anne Cournol

Jony Hudson Ben SauerMike Tarbutt