Searches for Permanent Electric Dipole Moments (EDM) of Atoms, Molecules, and the Neutron Dmitry Budker University of California, Berkeley Nuclear Science Division, LBNL 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 y z 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  -Vr, p, E, d = e  r, … A  AL = r  p, S, B Similarly for scalars (pseudo-scalars) Under Spatial Inversion (P): S  SEnergy, any V  V’, A  A’ … PS  -PSany 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 !

The theorists who said: check it ! Prof. T. D. Lee Prof. C. N. Yang

Prof. C. S. Wu ( ) 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 T j μ = (ρ,j) → (ρ,-j) → (ρ,j) Time component is associated with energy → to flip sign, try C CPT j μ = (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) · SUSY Left-Right Symmetric SO(10) GUT … e1.6 · μ p (from 199 Hg) 4 · Hg3.1 · 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 Electric fieldNumber of Particles Coherence Time Lifetime of Experimentalist

EDM of the Electron Heavy atoms and molecules amplify the EDM (d at / d e ~ Z 3 α 2 P.G.H. Sandars, Oxford, 1960s) Best current limit |d e |<1.5· e·cm from E.D. Commins et al ( ), Tl A challenge is set !

Professor Eugene D. Commins

ComminsFest Symposium May 20-21, 2001, Berkeley

ComminsFest Book

Atomic EDMs measured in JI Rb1/23/2,5/2 Cs1/27/2 Fe 3+ 3/ Tl1/2 129 Xe 3 P 2 21/2 129 Xe 1 S 0 01/2 199 Hg01/2 Also proposed/considered/pursued: you name it ! Ra, Rn, Dy, Sm, Yb, Ba, Au, Fr, Gd 3+ 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 (~ 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/cm 3 Storage time:  = 130 s E = 4.5 kV/cm 199 Hg co-magnetometer Statistics-limited

The LANSCE/SNS n-EDM experiment Features :  Create UCN in place in 4 He  3 He comagnetometer  HV for E field generated internally  SQUIDs to detect 3 He spin precession  3 He capture/ 4 He scintillation detection

UCN Source

Neutron EDM experiment at LANSCE Light Guides Cells Between Electrodes HV and Ground Electrodes Beam Entrance Window HV Variable Capacitor SQUID Enclosure Cos  Coil

Polarized 3 He Source Justin Torgerson Steve Lamoreaux

3 He 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 E  v systematics: 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 Hz  c ~L/v Motional magnetic field ~5·10 -8 Hz for both n and 3 He

E-field requirements Homogeneity over cell volume Stability over 500 s< 1 % Reversibility This reduces E-field-related systematics to < 5  Hz, i.e. one tenth of the EDM shift for d n = e  cm Electric field monitoring ~ 0.1% -1%

The Kerr Effect Uniaxial E-field-induced anisotropy:  n = n || -n  = KE 0 2 For input light polarized at 45 o to E, the induced ellipticity: Circular analyzer Achievable sensitivity:   rad Hz -1/2

Electric Field Measurement Kerr constant for LHe estimated from experimental data for He at 300K: K ≈ 1.7 · (cm/V) 2 Electric field: E 0 = 50 kV/cm Sample length: L = 10 cm Induced ellipticity:  ≈ rad A 1s measurement gives accuracy (  ≈ rad Hz -1/2 ):  E 0 /E 0 ≈ 5 · ? Kerr constant for superfluid He ?

Test set-up at Berkeley Cryostat (T  1.4 K) with optical access Graduate student A. Sushkov Electrode Assembly Laser Home-made cryogenic HV cable HV cable- connector Copper electrodes l=38 mm gap=6 mm Thin-wall st. steel tube

Results: LN 2 Kerr constant E = 60 kV/cm max Measurement: K = 4.2(1)· (cm/V) 2 Literature result: K = 4.0 · (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 CooperA. Sushkov, Val Yashchuk, S. Lamoreaux Eric Williams

Results: LHe Kerr constant (T≈1.4 K) E = 50 kV/cm max Measurement: K = 2.45(13)· (cm/V) 2 Theoretical value: (1s, 2s, 2p levels) K = 2.0 · (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 !