The EDM of electrons, neutrons, & atoms

A new measurement of the electron edm

E.A. Hinds

Birmingham, 26 October 2011

Centre for Cold Matter

Imperial College London

+ +

+ +

polarisable vacuum with increasingly rich structure at shorter distances:

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

How a point electron gets structure

-

point electron

electron spin

+ -

edm

Electric dipole moment (EDM)

T + -

If the electron has an EDM, nature has chosen one of these,

breaking T symmetry . . . CP

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)

Standard Model 4

The interesting region of sensitivity

Theoretical estimates of eEDM

Insufficient CP

to make universe

of matter

e e

g selectron

electron

de

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

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

This is very small

E

= 3 x 10-19 Debye

When does mB.B equal this ? B _ 1 fG ~

The magnetic moment problem

5

A clever solution

E

electric field

hde

amplification

atom or molecule containing electron

(Sandars 1964)

For more details, see E. A. H. Physica Scripta T70, 34 (1997)

Interaction energy

-de hE•

F P Polarization factor

Structure-dependent relativistic factor

Z3

6

Our experiment uses a molecule – YbF

EDM interaction energy is a million times larger (mHz)

needs nG stray B field control

0

5

10

15

20

0 10 20 30

Applied field E (kV/cm)

Eff

ecti

ve f

ield

hE

(G

V/c

m)

Amplification in YbF

16 GV/cm

7

| -1 > | +1 >

| 0 >

The lowest two levels of YbF

Goal: measure the splitting 2dehE to ~1mHz

F=1

F=0

E

-dehE

+dehE

+

-

+

-

X2S+ (N = 0,v = 0)

170 MHz

8

Pulsed YbF beam

Pump A-X Q(0) F=1

Probe A-X Q(0) F=0

PMT

F=1

F=0

rf pulse

B HV+

HV-

How it is done

Ch 15 Cold Molecules, eds. Krems, Stwalley and Friedrich, (CRC Press 2009)

1

1.0

0.0

Flu

ore

scen

ce

Measuring the edm

Applied magnetic field

Det

ecto

r co

un

t ra

te

B

-E E

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

de

-B

10

Modulate everything

• Generalisation of phase-sensitive detection

• Switch periodically on short timescale

but randomly on long timescale.

• Measure all 512 correlations.

±E ±B

±B

±rf2f ±rf1f

±rf2a ±rf1a

±laser f ±rff

spin interferometer

signal

9 switches: 512 possible correlations

11

** 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.

• A random blind offset is added that only the computer knows.

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

12

Measuring the other 511 correlations

correlation mean mean/

fringe slope calibration beam intensity f-switch changes rf amplitude E drift

E asymmetry E asymmetry inexact π pulse

• Nearly all are zero (as they should be) !

13

The only systematic error correction

• Electric field “reversal” changes magnitude of E (slightly) causing a Stark shift

We measure and correct: (+5.5 ± 1.1) ×10-28 e.cm.

• rf detuning from resonance

We measure this by the {rf1f.B} and {rf2f.B} correlations they are both ~ 100 nrad/Hz

makes a (small) interferometer phase shift

We measure this by the {rf1f.E} and {rf2f.E} correlations

• Together false EDM

14

• Magnetic field noise B fluctuations have some component synchronous

with E reversal:

We measure and correct: (-0.3 ± 1.7) ×10-28 e.cm.

B synchronous with E reversal

ED

M

EDM noise

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

bootstrap method determines distribution

16 -5 5 0

Gaussian distribution

Distribution of edm/edm

?? ± 5.7 ×10-28 e.cm

includes blind offset

68% confidence level

2

1

0

-1

-2

EDM (10-25 e.cm)

25 million beam shots

Current status

de = (-2.4 5.7 1.5) ×10-28 e.cm

68% statistical systematic - limited by statistical noise

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

• Previous result - Tl atoms

de < 2.0 × 10-27 e.cm with 90% confidence

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

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

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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 ready to explore this region

(if funded)

Standard Model

de < 1 x 10-27 e.cm

New excluded region

18

New cryogenic buffer gas source of YbF

YbF beam

YAG ablation laser

3K He gas cell

Yb+AlF3

target

19

15 more molecules/pulse

=> 10 better signal:noise ratio

3 longer interaction time (slower beam)

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

d(muon) 7×10-19

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) 3×10-26 10-26

YbF

Summary e- EDM is a direct probe of physics beyond SM

Atto-eV molecular spectroscopy tells us about TeV particle physics!

specifically probes CP violation (how come we’re here?)

absence of EDM suggests no min. supersymmetry

Mike Tarbutt Ben Sauer

EDM Group Members

Jony Hudson EAH

Dhiren Kara Joe Smallman

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