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Searches for Permanent Electric Dipole Moments (EDM) of Atoms, Molecules, and the Neutron

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. http://budker.berkeley.edu/. The Plan:. Discrete vs. continuous symmetries P, CP, CPT

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Searches for Permanent Electric Dipole Moments (EDM) of Atoms, Molecules, and the Neutron

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

  2. 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

  3. P x’ z’’ z’ y’ Rotation around y’ x’’ • Left hand cannot be rotated into right hand ! y’’=y’ What is parity? z y x

  4. Normal vs. axial vectors • Under Spatial Inversion (P): • V  -V r, p, E, d = er, … • A  A L = rp, S, B Similarly for scalars (pseudo-scalars) • Under Spatial Inversion (P): • S  S Energy, any VV’, AA’ … • PS  -PS any A V, …

  5. 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

  6. 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 !

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

  8. Prof. C. S. Wu (1913-1997) The shatterer of the parity illusion (1956)…

  9. The Co-60 experiment

  10. 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)

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

  12. CPT theorem: a “proof” y y y x x x • For an even-dimensional space, P=rotation P Rotation Prof. Iosif B. Khriplovich • Our space-time has 4 dimensions → try PT • P T • jμ = (ρ,j) → (ρ,-j) → (ρ,j) ☺ • Time component is associated with energy → to flip sign, try C • CPT • jμ = (ρ,j) → (-ρ,-j)

  13. T P Permanent EDM of a particle contradicts bothP- and T-invariance d J

  14. EDMs of various particles (e·cm) EDM experiments have killed MOST models of CP-violation in Kaons !

  15. EDM causes spin to precess in an electric field z E y x

  16. Lifetime of Experimentalist Universal Statistical Sensitivity Formula Electric field Number of Particles Coherence Time

  17. 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 !

  18. Professor Eugene D. Commins

  19. ComminsFest SymposiumMay 20-21, 2001, Berkeley

  20. ComminsFest Book

  21. Atomic EDMs measured in Also proposed/considered/pursued: you name it ! Ra, Rn, Dy, Sm, Yb, Ba, Au, Fr, Gd3+ Molecular EDMs measured in Also proposed/considered/pursued: LuO, CsF, PbF, PbI, BiO, BiS, YbH, VdV molecules, e.g., CsXe, PbO*

  22. ? Neutron EDM: the time line Prof. N. F. Ramsey Retires

  23. Prof. Norman F. Ramsey “What if we see an EDM?”

  24. Ultra-Cold Neutrons (UCN) • 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) Materials used for UCN storage: The ILL UCN Source

  25. 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

  26. 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

  27. UCN Source

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

  29. Polarized 3He Source Justin Torgerson Steve Lamoreaux

  30. 3He as Analyzer

  31. Concept for HV generator 500 kV 50 kV Variable capacitor in LHe volume

  32. Accurate E-reversal, stability and field-monitoring are essential! The Ev systematics: ~3 Hz c~L/v Motional magnetic field ~5·10-8 Hz for both n and 3He 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

  33. E-field requirements • Homogeneity over cell volume • Stability over 500 s < 1 % • Reversibility This reduces E-field-related systematics to < 510-10 Hz, i.e. one tenth of the EDM shift for dn=10-28 e cm Electric field monitoring ~ 0.1% -1%

  34. 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 • Achievable sensitivity:   10-8 rad Hz-1/2

  35. Electric Field Measurement Kerr 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 ?

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

  37. E = 60 kV/cm max Results: LN2 Kerr constant 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)

  38. LHe Kerr Constant Measurements Eric Williams Martin Cooper A. Sushkov, Val Yashchuk, S. Lamoreaux

  39. Results: LHe Kerr constant (T≈1.4 K) E = 50 kV/cm max • 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!

  40. 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 And our book w/ Kimball & DeMille ! PbO* (e-EDM) Hg, LXe (a radically new approach)

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