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Searches for atomic electric dipole moments

Matthew R. Dietrich. Assistant Physicist Argonne National Laboratory. Searches for atomic electric dipole moments. Electric Dipole Moments and Discrete Symmetries. Electric dipole moment (EDM): displacement vector from a particle’s center of mass to its center of charge.

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Searches for atomic electric dipole moments

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  1. Matthew R. Dietrich Assistant Physicist Argonne National Laboratory Searches for atomic electric dipole moments

  2. Electric Dipole Moments and Discrete Symmetries • Electric dipole moment (EDM): • displacement vector from a particle’s center of mass to its center of charge. • violates both P-parity (spatial inversion) and T-time reversal symmetries: • Assuming the combination of C-charge conjugation (particle <-> antiparticle), P, and T is conserved: • T-violation implies CP-violation • EDMs are a very sensitive probe of CP-violation

  3. EDM Sectors Neutrons Paramagnetic Diamagnetic Hg, Ra, Xe, TlF ThO, YbF, Cs, Tl, Fr…

  4. Atomic edms • The EDM of an atom would arise from one of its constituent parts, for example: • The EDM of the electron • Only in paramagnetic atoms • The Schiff moment of the nucleus • Paramagnetic or diamagnetic • The Magnetic Quadrupole Moment of the nucleus • Paramagnetic only • Generally, the EDM of a paramagnetic atom is sensitive to all of the above mechanisms. Physical arguments are usually employed to establish one effect that dominates. In paramagnetic atoms and molecules, the electron is usually thought to dominate. • Molecules are special because the E-field is fixed by the internal structure of the molecule. So their “EDM” isn’t linear in the applied field, like a proper EDM is. But the same principles hold for this “CP-violating frequency shift”.

  5. Schiff Moments and EDMs • Leonard Schiff’s Theorem (1963): • Any permanent dipole moment of the nucleus is perfectly shielded by its electron cloud • True for point-like nuclei, non-relativistic electrons • However, the “Schiff moment” is not shielded by this effect • Zero for point-like, spherical nuclei • Arises from deformations in the nucleus or its constituent nucleons • Very large in nuclei with both a quadrupole and octupole deformation Schiff Moment Look for heavy nuclei with large quadrupole and octupole deformations!

  6. Techniques Standard disclaimer: Roughly speaking, and incomplete lists… How to prepare and detect state of sample? How to create uniform and constant electric and magnetic fields?

  7. What is common • All EDM experiments must solve a few problems in common • How to collect a sample of identical particles • Beam, vapor cell, cold atom trap, etc. • How to prepare the spin • Optical pumping, SEOP, magnetic filter, etc. • How to isolate the spin while it precesses, to create the longest coherence time • Magnetic shielding, low gradients, etc. • How to detect the spin • Optical, SQUID magnetometer, radioactive decay, etc.

  8. What is common • The DiVincenzo criteria for quantum computation are • A scalable physical system with well-characterized qubits • The ability to initialize the state of the qubit • Long relevant decoherence times • A qubit-specific measurement capability • Also: A universal set of quantum gates Quantum computation and precision measurement share technical challenges with some frequency, motivating the field of quantum sensors. Technics or devices can be shared for the betterment of both. • All EDM experiments must solve a few problems in common • How to collect a sample of identical particles • How to prepare the spin • How to isolate the spin while it precesses, to create the longest coherence time • How to detect the spin

  9. Beam experiments • A cold, collimated beam of molecules is produced by buffer gas cooling • The beam is then optically prepared and detected (usually) • Because of Exv and the large gap size, maximum E field is generally limited • Lifetimes measured in milliseconds

  10. Molecules and edms 290 MV/cm F- 224 pm Nuclei experience fields of 100’s MV/cm, while the electron experiences 100’s GV/cm Ra+ Compare with 250 kV/cm in the new generation of electrodes This effect allows beam experiments to use low applied fields, yet still achieve good limits on the EDM (Courtesy ACME)

  11. Molecules and edms 290 MV/cm F- 224 pm Nuclei experience fields of 100’s MV/cm, while the electron experiences 100’s GV/cm Ra+ Compare with 250 kV/cm in the new generation of electrodes

  12. Unit EDM +e cm -e The Seattle mercury EDM Experiment Properties of Hg-199 and experiment • Stable • Spin I=½ nucleus (no quadrupole moment) • Nuclear T2 ~ 100-200 seconds • High Vapor Pressure at room temperature, 4*10^13 cm-3 • High Z=80 • Nearly spherical nucleus • Glass cell limits E field to 10 kV/cm • Leakage current through cell is leading systematic EDM(Hg-199) < 7 x 10-30 e cm If Hg nucleus is size of earth, then this is two charges separated by 50 pm Griffith et al., Phys Rev Lett (2009) Graner et al., Phys Rev Lett (2016)

  13. HeXe EDM experiment at BMSR-2 (Berlin) EDM measurement using comagnetometer Goal: 100x improvement on previous value, • Current status: • Results from an initial 2017 measurement expected Fall 2018 • Limited by statistics, not systematics • Blinded • 2017 EDM sensitivity comparable to Rosenberry and Chupp (2001) result • Completed 2018 data collection, potentially 10x improvement in sensitivity • Future: • Improved SNR (better gas purity, increased polarization, lower SQUID noise with upgraded dewar) • Improved systematic control (cell shape optimization, better leakage current monitoring, cell motion measurement) • Increased electric field (higher gas pressure, bipolar HV) • 10-100x improvement in EDM sensitivity M. A. Rosenberry and T. E. Chupp, Phys. Rev. Lett. 86, 22 (2001) Slide courtesy Natasha Sachdeva

  14. |a |b Radium EDM - = (|a - |b)/2 + = (|a + |b)/2 • A closely spaced parity doublet enhances the • appearance of parity violating terms in the • underlying Hamiltonian • – Haxton & Henley (1983) 55 keV • A large quadrupole and • octupole deformation results • In an enhanced Schiff moment • – Auerbach, Flambaum & Spevak (1996) Relativistic atomic structure weakens the Schiff theorem, resulting in a strong enhancement with increasing Z (225Ra/199Hg ~ 3) – Dzuba, Flambaum, Ginges, Kozlov (2002) J. Engel et al., Progress in Particle and Nuclear Phys. (2013)

  15. Radium Setup Transverse Cooling HV Electrodes Ra(NO3)2+Ba Oven Zeeman Slower Magnetic Shielding & Magnet Coils h ~ 1.6*10^-6 (Low vapor pressure) For EDM: Ra-225 I = 1/2, J = 0 t1/2 = 15 days For Testing: Ra-226 I = 0, J = 0 t1/2 = 1600 yrs 226Ra MOT 200,000 atoms 40 mK 0.6 mm J. R. Guest et al., PRL 98 093001 (2007)

  16. Transfer Atoms from MOT to “Bus” ODT “Bus” ODT 50 W 1550 nm Magnetic Shielding & Magnet Coils Translation Stage Lens 0.03 mm MOT + ODT 80% Efficiency 0.6 mm

  17. Transfer Atoms from “Bus” to “Holding” ODT “Bus” ODT 50 W 1550 nm Magnetic Shielding & Magnet Coils Lens 30 mG HV Electrodes Glass Tube Vacuum chamber 10-11 Torr 70 kV/cm

  18. Transfer Atoms from “Bus” to “Holding” ODT “Bus” ODT 50 W 1550 nm Magnetic Shielding & Magnet Coils Standing Wave “Holding” ODT 10 W 1550 nm Lens Traveling Wave “Bus” ODT

  19. Transfer Atoms from “Bus” to “Holding” ODT “Bus” ODT 50 W 1550 nm Magnetic Shielding & Magnet Coils Standing Wave “Holding” ODT 10 W 1550 nm Lens Laser Cooling 100 mW 714 nm Laser Cooling and B Field Traveling Wave “Bus” ODT

  20. Transfer Atoms from “Bus” to “Holding” ODT Atoms Magnetic Shielding & Magnet Coils Standing Wave “Holding” ODT 10 W 1550 nm .5 mm ODTODT Transfer: 70% Efficiency 700 atoms Ra-225 .5 mm R. H. Parker et al., PRC 86, 065503 (2012) Absorption Imaging

  21. EDM result M. Bishof et al. PRC 94, 025501 (2016)

  22. EDM result dRa-225 = (4± 6stat ± 0.2syst) × 10-24 e-cm dRa-225 < 1.4 × 10-23 e-cm 95% C.L. M. Bishof et al. PRC 94, 025501 (2016)

  23. Systematics M. Bishof et al. PRC 94, 025501 (2016)

  24. Improvement 1: Increased Field Previously: Copper Electrodes, E = 70 kV/cm Niobium electrodes newly installed: >200 kV/cm demonstrated (J. Singh/MSU, M. Kelly, T. Reid/ANL, M. Poelker/Jlab) Phys. Rev. Spec. Top. – Acc. and Beams, 15, 083502 (2012) Factor of ~4 increase in EDM Sensitivity Combined with improvement in detection efficiency (STIRAP) and increased source, we expect about 100 fold improvement in next measurement

  25. Effect on Standard Model Extensions T. Chupp and M. Ramsey-Musolf, PRC 91, 035502 (2015) At the level available with those upgrades, radium will improve significantly on the global sensitivity for all parameters

  26. Phase space in electron edm T. Fleig, M. Jung, JHEP 2018: 12

  27. Phase space in electron edm T. Fleig, M. Jung, JHEP 2018: 12

  28. Blue without new Xenon result Green with 3e-29 e cm sensitivities Global Limit Preliminary Ra-225 EDM (1-sigma e-cm) Improved Xe result strengthens new Ra result, and vice versa

  29. Two-Higgs Doublet • 2HDM is a simple extension to the SM allowing for CP-violation and natural mechanisms for baryogenesis • Radium has strong sensitivity to 2HDM, in spite of electroweak nature of theory • Complementary to electron EDM, which exhibits interference LANL neutron EDM (Green) Future electron EDM (blue) Radium Blue Slower (yellow) 10^-27 e-cm S. Inoue, M. J. Ramsey-Musolf, Y. Zhang Phys. Rev. D 89, 115023 (2014) C.-Y Chen, H.-L Li, M. J. Ramsey-Musolf, Phys. Rev. D 97, 015020 (2018)

  30. Right-handed charged currents • Apparent tension in CP-violating parameters from Kaon decays could be explained by a right-handed charged weak current, which would be detectible with Hadronic EDM experiments • Due to large theoretical uncertainties in Hg, present constraints on such a model are very weak • The upcoming radium measurement will be sensitive to this possibility STIRAP + HV Blue Slower V. Cirigliano, W. Dekens, J. de Vries, and E. Mereghetti, Phys. Lett. B 767, 1 (2017) arXiv:1708.00797v2

  31. How to trap a molecule: photoassociation • Excite diatom to electronically excited bound state • The radiative decay carries away the excess energy • Pro: molecule is already cold when created • Con: both atoms in molecule have to be laser coolable • See Timo Fleig’s talk next week • If you can trap two different atoms in a MOT, why not just wait until they collide? • The reaction is hugely exothermic! The newly formed molecule would be ejected from the trap • Use light to form a more gentle reaction

  32. How to trap a molecule: Direct laser cooling O O O 191 pm 220 pm Sr Sr Sr Valence electrons bind the molecule… Causing a change in bond length when excited… And vibrational excitations after relaxation. There are many possible final states, which makes laser cooling intractable

  33. How to trap a molecule: Direct laser cooling F- F- F- 221 pm 220 pm 220 pm Sr+ Sr+ Sr+ Fluorine is so polarizing, it steals one electron from strontium, leaving the second attached to the Sr… This second electron is the least tightly bound, and serves as the valence electron… So the bond length is unchanged during electronic excitation! Vibrations are rarely excited in this kind of molecule!

  34. How to trap a molecule: Direct laser cooling F- F- F- 221 pm 220 pm 220 pm Sr+ Sr+ Sr+ Nature467, 820–823 (2010) Nature512, 286-289 (2014)

  35. How to trap a molecule: Direct laser cooling H F O Sr Sr Nothing special about the fluorine, besides being very polar… So is OH! PRL 118, 173201 (2017) You can (usually) replace atoms with isoelectric atoms or groups and still get laser coolable molecules

  36. Radium Molecules SrF is already known to be laser-coolable Guess who is similar to strontium… F F RaF is also thought to be laser coolable Sr Ra Phys. Rev. A 82, 052521 arXiv: atom-ph/1302.5682 F Tl Ra N Tl Or better yet a diamagnetic version

  37. Radium Molecules SrF is already known to be laser-coolable Guess who is similar to strontium… F F RaF is also thought to be laser coolable Sr Ra Phys. Rev. A 82, 052521 arXiv: atom-ph/1302.5682 F Tl Ra N Tl Or better yet a diamagnetic version

  38. Octupole deformation + molecule The combination of huge internal molecular fields plus enhanced octupole deformation promise future experiments of tremendous sensitivity to new physics But the path is long Step 1: Spectroscopy. Start with stable barium as a proxy for radium.

  39. Ion trap edm H. Loh et al., Science 342, 1220 (2013) An ion trap is formed with a hexapole, rotating electric field, and a DC magnetic quadrupole field, outwardly facing The ion and its polarization rotates around in a circle, always phase-locked to the direction of the magnetic field This requires that the molecule is very easily polarized (about 10 V/cm), placing somewhat demanding constraints on the electronic structure

  40. Atom Trappers @ Argonne mdietrich@anl.gov + Donald Booth, Josh Abney DOE Office of Nuclear Physics

  41. sensitivities Assuming new Xe result Global Limit Preliminary Ra-225 EDM (1-sigma e-cm)

  42. EDM Measurements B

  43. EDM Measurements B E

  44. EDM Measurements B E

  45. EDM Measurements B E

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