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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
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)
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) ☺
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 !
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 !
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*
•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
Neutron EDM experiment at LANSCE
Light Guides Cells BetweenElectrodes
HV and Ground Electrodes
Beam Entrance Window
HV Variable Capacitor
SQUID Enclosure
Cos Coil
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)
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 !