Searches for Permanent Electric Dipole Moments (EDM)

of Atoms, Molecules, and the Neutron

Dmitry BudkerUniversity of California, Berkeley

Nuclear Science Division, LBNL

http://budker.berkeley.edu/http://budker.berkeley.edu/

March, 2010

The Plan:

• Discrete vs. continuous symmetries

• P, CP, CPT

• EDM and P,T-violation

• How EDM experiments work?

• A brief and incomplete survey

• The LANL neutron EDM experiment

• Kerr Effect in Liquid Helium

What is parity?

x

yz

P

x’

y’ z’

x’’

z’’

y’’=y’

Rotation around y’

Left hand cannot be rotated into right hand !

Normal vs. axial vectors

Under Spatial Inversion (P):

• V -V r, p, E, d = er, …

• A A L = rp, S, B

Similarly for scalars (pseudo-scalars)

Under Spatial Inversion (P):

• S S Energy, any VV’, AA’ …

• PS -PS any A V, …

Discrete vs. Continuous Transformations and Symmetries

• Continuous:

• Translation → momentum conservation

• Translation in time → energy conservation

• Rotation → angular momentum conservation

• Discrete:

• Spatial Inversion (P) → P-invariance (parity)

• Charge Conjugation (C) → C-invariance

• Time reversal (T) → T-invariance

• CP

• CPT

• Permutation of identical particles → PSP, spin-statistics

The (broken) law of parity

Because the laws of Nature should be the same in the “real” world and its mirror image, no pseudo-scalar correlation should be observed in experiments, for example

Does not apply to cork-screws !

pI

The theorists who said: check it !

Prof. T. D. LeeProf. C. N. Yang            

Prof. C. S. Wu (1913-1997)

The shatterer of the parity illusion (1956)…

The Co-60 experiment

CP, CPT, P and T

• Symmetry is restored by CP (L.D. Landau, and others)

• CP-violation discovered in 1964 (Cronin, Fitch, et. al.)

• Important for matter-anti-matter asymmetry

• Only K-mesons, and since very recently, also B-mesons

• CPT is still good (for now)

Prof. James Cronin lecturing on CP-violation in Kaon decays Novosibirsk, USSR, September 1986

CPT theorem: a “proof”

Prof. Iosif B. Khriplovich

• For an even-dimensional space, P=rotation

x

y

P

x

y

x

y

Rotation

• Our space-time has 4 dimensions → try PT

P Tjμ = (ρ,j) → (ρ,-j) → (ρ,j)

• Time component is associated with energy → to flip sign, try C

CPT jμ = (ρ,j) → (-ρ,-j) ☺

Permanent EDM of a particle contradicts both

P- and T-invariance

PT

d

J

EDMs of various particles (e·cm)

Present upper limit on |d|

Experimental reach (???)

Standard

Model (SM)

Beyond SM

n (6-10) ·10-26 10-28 10-34-10-31

SUSY

Left-Right Symmetric

SO(10) GUT

…

e 1.6 ·10-27 10-30 10-40-10-38

μ 10-18 10-24 10-38

p (from 199Hg) 4 ·10-24 10-25 10-34-10-31

199Hg 3.1 ·10-29 10-29 EDM experiments have killed MOST models of CP-violation in Kaons !

EDM causes spin to precess in an electric field

E

x

y

z

Universal Statistical Sensitivity Formula

TNEd

11

4

2

Electric field Number of Particles Coherence Time

Lifetime of Experimentalist

EDM of the Electron

• Heavy atoms and molecules amplify the EDM (dat/ de~ Z3α2 P.G.H. Sandars, Oxford, 1960s)

• Best current limit |de|<1.5·10-27 e·cm from E.D. Commins et al (1985-2001), Tl

• A challenge is set !

Professor Eugene D. Commins

ComminsFest Symposium May 20-21, 2001, Berkeley

ComminsFest Book

Atomic EDMs measured inJ I

Rb 1/2 3/2,5/2

Cs 1/2 7/2

Fe3+ 3/2 0205Tl 1/2 1/2

129Xe 3P2 2 1/2129Xe 1S0 0 1/2

199Hg 0 1/2

Also proposed/considered/pursued: you name it ! Ra, Rn, Dy, Sm, Yb, Ba, Au, Fr, Gd3+

Molecular EDMs measured in

TlF

YbF

Also proposed/considered/pursued:

LuO, CsF, PbF, PbI, BiO, BiS, YbH, VdV molecules, e.g., CsXe,

PbO*

Neutron EDM: the time line

?Prof. N. F. Ramsey

Retires

Prof. Norman F. Ramsey

“What if we see an EDM?”

•Proposal: Ya. B. Zel'dovich, Sov. Phys. JETP, 9, 1389 (1959)•First realizations: 1969, Dubna and Garching•Problem with production -- tiny fraction in Maxwellian distribution (~10-11 at T=30 K)

Ultra-Cold Neutrons (UCN)

The ILL UCN

Source

Materials used for UCN storage:

The ILL n-EDM Experiment

• Ramsey separated-field method

• N = 13,000; n~1/cm3

• Storage time: = 130 s

• E = 4.5 kV/cm

• 199Hg co-magnetometer

• Statistics-limited

TNEd

11

4

2

The LANSCE/SNS n-EDM experiment

Features :

Create UCN in place in 4He

3He comagnetometer

HV for E field generated internally

SQUIDs to detect 3He spin precession

3He capture/4He scintillation detection

UCN Source

Neutron EDM experiment at LANSCE

Light Guides Cells BetweenElectrodes

HV and Ground Electrodes

Beam Entrance Window

HV Variable Capacitor

SQUID Enclosure

Cos Coil

Polarized 3He Source

Justin Torgerson

Steve Lamoreaux

3He as Analyzer

Concept for HV generator

50 kV

500 kV

Variable capacitor in LHe volume

Accurate E-reversal, stability and field-monitoring are essential!

The Ev systematics:

02

2

c

2

LB

cEv

/

S. K. Lamoreaux, PRA 53(6), R3705, 1996

D. Budker, D. F. Kimball, and D. P. DeMille, “Atomic physics: Exploration in Problems and Solutions,” Oxford, 2003

~3 Hzc~L/vMotional

magnetic field ~5·10-8 Hz for both n and 3He

E-field requirements

• Homogeneity over cell volume

• Stability over 500 s < 1 %

• ReversibilityThis reduces E-field-related systematics to < 510-10 Hz,

i.e. one tenth of the EDM shift for dn=10-28 e cm

Electric field monitoring ~ 0.1% -1%

The Kerr Effect • Uniaxial E-field-induced anisotropy:

n = n||-n= KE02

• For input light polarized at 45o to E, the induced

ellipticity:

• Circular analyzer

21

21

II

II

• Achievable sensitivity: 10-8 rad Hz-1/2

20// KELnL

Electric Field MeasurementKerr constant for LHe estimated from experimental data for

He at 300K: K ≈ 1.7·10-20(cm/V)2

Electric field: E0 = 50 kV/cm

Sample length: L = 10 cm

Induced ellipticity: ≈ 10-5 rad

A 1s measurement gives accuracy ( ≈ 10-8 rad Hz-1/2):

E0/E0 ≈ 5·10-4

? Kerr constant for superfluid He ?

Test set-up at BerkeleyCryostat (T 1.4 K) with optical access

Graduate student A. Sushkov

Electrode Assembly

LaserHome-made cryogenic HV cable

HV cable- connector

Copper electrodes l=38 mm gap=6 mm

Thin-wall st. steel tube

Results: LN2 Kerr constant

E = 60 kV/cmmax

Measurement:

K = 4.2(1)·10-18 (cm/V)2

Literature result:

K = 4.0·10-18 (cm/V)2

K.Imai et. al., Proceedings of the 3rd Int. Conf. On Prop. and App. Of Diel. Mat., 1991 Japan)

LHe Kerr Constant Measurements

Martin Cooper A. Sushkov, Val Yashchuk, S. Lamoreaux

Eric

Will

iam

s

Results: LHe Kerr constant (T≈1.4 K)

E = 50 kV/cmmax

Measurement:

K = 2.45(13)·10-20 (cm/V)2

Theoretical value:

(1s, 2s, 2p levels)

K = 2.0·10-20 (cm/V)2

Temperature dependence!

Summary

• EDM experiments are among the most sensitive probes of Physics Beyond the Standard Model

• Steady progress in atoms and molecules

• Progress with n-EDM has slowed down in 1990s, but radically new experiments are in preparation; optimistic prospects (if funded)

• Kerr effect in He for the LANL experiment

• Only a few experiments were mentioned in this talk; vast literature available (e.g., book by Khriplovich&Lamoreaux)

•EDM-related colloquia (recorded):

D. DeMille M. Romalis

PbO* (e-EDM) Hg, LXe (a radically new approach)

And our book w/ Kimball &

DeMille !