Progress Report on A New Search for a Permanent Electric Dipole Moment of the Electron in a Solid St

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Progress Report on A New Search for a Permanent
Electric Dipole Moment of the Electron in a
Solid State System
Peterhof, 5th International UCN workshop, July
14 2005 Chen-Yu Liu, S. K. Lamoreaux G. Gomez,
J. Boissevain, M. Espy, A. Matlachov Los Alamos
National Laboratory

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Shapiros proposal -- using a solid state system
to measure eEDM
Usp. Fiz. Nauk., 95 145 (1968)
B.V. Vasilev and E.V. Kolycheva, Sov. Phys.
JETP, 47 2 243 (1978) de(0.81 ? 1.16)?10-22
e-cm
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Features of solid state eEDM experiment
Pros

• High number density of bare electrons 1022/cm3.
• PbO Cell Tl Beam
• N nV 1016 N nV 108
• Electrons are confined in solid ? No motional
  field effect.
• Solid state sample
• Large magnetic response.
• Solid state sample
• High dielectric strength.
• Concerns
• Parasitic, hysteresis solid state effects might
  limit the sensitivity to the EDM signals .

Cons
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Figure of Merit

• Sensitive magnetometers
• Superconducting Quantum Interference Device
  (SQUID).
• Atomic cell (non-linear Faraday effect).
• Measure induced magnetic flux

d?de, enhancement factor ? ? Z3
Pick-up coil area
Large Z
Large A
Effective field, large dielectric constant K.
Paramagnetic susceptibility ?m
Large E
Large ?m
A paramagnetic insulating sample
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New experiment
Gadolinium Gallium Garnet (Gd3Ga5O12) polycryostal
Better SQUID design

• Gd3 in GGG
• 4f75d06s0 ( 7 unpaired electrons).
• Atomic enhancement factor -4.9?1.6.
• Langevin paramagnet.
• Dielectric constant 12.
• Low electrical conductivity and high dielectric
  strength
• Volume resistivity 1016 ?-cm.
• Dielectric strength 10 MV/cm for amorphous
  sample.
• Cubic lattice.

Higher E field 10kV/cm
Large Sample size 100 cm3
Lower Temperature 50mK
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Enhancement Factor of EDMof electrons in Gd3 in
garnet crystal

• Buhmann, Dzuba, Sushkov, Phys. Rev. A 66, 042109
  (2002).
• Dzuba, Shushkov, Johnson, Safronava, Phys. Rev.
  A 66, 032105 (2002).
• Kuenzi, Sushkov, Dzuba, Cadogan, Phys. Rev. A
  66, 032111 (2002).
• Mukhamedjanov, Dzuba, Sushkov, Phys. Rev. A 68,
  042103 (2003).

The enhancement factors (incomplete E field
shielding effects) has two contributions Electro
ns in atom Katom Adjacent Oxygen electrons
KCF
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EDM Sensitivity Estimate
S. K. Lamoreaux, Phys. Rev. A 66, 022109 (2002)

• EDM signal ?p 17??0 per 10-27e-cm.
• with 10kV/cm, T10mK, A100 cm2 around GGG
• SQUID noise ??sq 0.2??0/vt (research quality)
• Coupling eff. ?sq/?p v(LsqLi)/(LpLi)
  8?10-3.
• Lsquid 0.2 nH.
• Lpick-up 700 nH. (gradiometer)
• Linput 500 nH.
• de ??sq/?sq(0.2??0/vt)/(8?10-3 ? ?p)
• de 1.47?10-27 /vt e-cm
• In 10 days of averaging, de 10-30 e-cm.

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Ongoing nEDM experiment at LANL. M. Cooper and
S.K. Lamoreaux
In 10 days of data accumulation,
de 10-30 e-cm.
J.M.Pendlebury and E.A. Hinds, NIMA 440 (2000) 471
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Alumina Crucible
Parallel plate capacitor
Poly-crystalline GGG
Single crystal GGG
Solid State Reaction to synthesize ceramics
using oxide powders
E.E. Hellstrom et al., J. Am. Ceram. Soc., 72
1376 (1989)
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Susceptibility ?m Measurements
Traditional AC field method
LC resonance circuit method

• Paramagnetic susceptibility

• Toroid inductor with GGG core
• Resonant frequency

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Magnetic flux pick-up coil planar gradiometer

• Common mode rejection ratio of residual external
  B fluctuations.
• measured ratio 240 ? 0.4 area mismatch.
• Enhancement of sample flux pick-up.

A2
A1
A1A2

• EDM Measurement Sequence
• Reverse HV polarity
• monitor magnetization changes (AC flux change
  picked up by the SQUID)

2.5
5
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SQUID Magnetometer
M. Espy and A. Matlachov

• DC SQUID two Josephson junctions on a
  superconducting ring.
• Flux to voltage transformer.
• Energy sensitivity 5 at 50 mK.
• Flux noise 0.2 ??0/vHz.
• Field sensitivity typically fT/vHz.
• Currently, we are using commercially available
  SQUIDs (QD DC SQUID, model 50) and electronics
  (StarCryoelectronics, PFL-100, PCI-1000)
• Flux noise 3 ??0/vHz.

State of the art
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Instrumentation

• High Voltage Electrodes Macor coated with
  graphite.
• Magnetic Shield (shielding factor gt 109)
• Superconducting Pb foils (2 layers).
• High ? Metglas alloy ribbons in cryostat.
• An additional cylinder of Conetic sheet outside
  the cryostat.
• The whole assembly is immersed in L-He bath,
  which can be cooled by a high cooling power
  dilution refrigerator. (3.5mW at 120mK)

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1.5 K L-He Cryostat

• Fluxgate
• Shielding factor of the metglas shield 100
• Shielding factor of the Conetic half cylinder
  shields 5
• SQUID
• Learn to implement SQUIDs in our experiment
• Noise Measurement
• Vibrations Vibrations of pickup coil relative to
  the superconducting Pb can (trapped flux ? field
  fluctuations).
• Micro-sparks in HV feedthroughs/cables/connnection
  s
• Measure the Shielding Factor of
• the metglas shield (did not help)
• Pb shield (gt 108)
• Sensitivity Calibration
• Put current loops around the G10 dummy samples,
  and measure the SQUID response.to the applied
  flux in the pick-up coild region
• Flux transfer efficienty 1

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SQUID Noise Spectrum

• Two layers of Pb superconducting foil
• Vibrational peaks are gone
• Background Intrinsic SQUID noise
• 1/f corner of SQUID noise lt 1Hz

• One layer of Pb superconducting foil
• Clear vibrational peaks
• Background gt Intrinsic SQUID noise

Vibrational peaks
Baseline 27.5 ??0/rtHz
Baseline 5.8 ??0/rtHz
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Learning about the SQUID

• Adding current bypass capacitors to the ground
  greatly reduce the high frequency spark signals
  into the SQUID.
• Stability of the SQUID feedback circuit.
• A larger RC constant of the FB circuit makes the
  SQUID operation less sucesptible to the constant
  HV polarity switches.
• Normal vs. Superfluid Helium bath
• SQUID baseline jumping??? (even with no HV on
  electrodes)
• He bubbles forming near the electrode, trap
  charge and then drift upwards
• He bubbles trapped in the Pb can, change the
  pressure of the helium, and thus changes the
  operating point of the SQUID.
• Superfluid Helium seems provide a quieter
  magnetic environment.
• Smaller SQUID noise at lower temperatures???
• Intrinsic noise 1/?T
• Vibrational isolation (mechanical pump).

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We have been turning on the HV and taking data
using SQUID with GGG samples for 2 months.
Waveforms
HV monitor
ms
Current In the ground plate
ms
SQUID signal
ms
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eEDM signal
4K, 2.8kVpp, 1.13Hz, 50 minutes
Preliminary
SQUID signal (-2.68-5.5)?10-7 V (-0.66 -
2.8)?10-7 V (drift corrected) Leakage Current
(-46 - 1) ?10 pA
Preliminary Results
de(0.44 ? 0.88) ? 10-23 e-cm
B.V. Vasilev and E.V. Kolycheva, Sov. Phys.
JETP, 47 2 243 (1978) de(0.81 ? 1.16)?10-22
e-cm
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Systematic Effects

• Leakage current.
• lt10-14A, should be feasible at low temp.
• Currently measure a non-zero value. Use a copper
  coated surface to replace the graphite surface of
  the groud plates might improve the LC monitor.
• Displacement current at field reversal.
• Generate a large B field (helps to check SQUID
  functionality).
• Magnetize materials around the sample??? (put in
  another SQUID for field monitor)
• Solid State effects
• Linear magneto-electric effect.
• Deviation from cubic symmetry. ???
• Magnetic impurities. (no problem, as long as they
  dont move.)
• Spin-lattice relaxation ???
• Currently measuring
• Channel cross-talks
• Use an improved DAQ with better signal
  isolations, especially for the SQUID input
  channel.
• Try commercially available HV supplies with solid
  state polarity switch

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Conclusions and Future Plans

• The current setup is sensitive to eEDM signal
  10-23e-cm using a hour of data.
• Still fighting against systematic effects that
  give rise to non-zero signals.
• The prototype system cooled to 40 mK and 2 days
  of data averaging should have an eEDM sensitivity
  of 10-27e-cm.
• Results from the prototype experiment expected in
  the end of 2005.
• Second generation experiment using
• larger samples, (10 samples in parallel)
• and more sensitive magnetometers
• research grade SQUID (noise 0.2??0/?Hz)
• cryogenic atomic magnetometers (D. Budkers group
  in Berkeley)
• should further push the sensitivity of the
  experiment to 10-30 e-cm.

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A new generation of electron EDM searches
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Traditional way to measure eEDM --atomic vapor
experiments

• Spin precession frequency in EB(??) and EB(??)
  field.
• Neutral atoms.

N. Fortson, et al. Physics Today, June 2003, p.33
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Comparison with 1978 Experiment

• B.V. Vasilev and E.V. Kolycheva, Sov. Phys.
  JETP, 47 2 243 (1978)
• Sample Nickel Zinc ferrite
• dielectric strength 2kV/cm.
• Fe3 ?b 4 ?B . (uncompensated moment) ? 2
• Atomic enhancement factor 0.52. ? 1
• Magnetic permeability 11 (at 4.2K). (??m0.8)
  
• Electric permittivity ?2.2?0.2. (??0K)
• Cubic lattice.
• No magnetoelectric effect.
• Sample size 1cm in dia., 1mm in height. (0.08
  c.c.) ? 500
• E Field 1KV/cm, 30Hz reversal rate ? 10 (field)
• Temperature 4.2K ? 100 (pending spin-glass)
• rf-SQUID with a field sensitivity of 10-12 T. ?
  1000-10000
• dFe3 (4.2?6.0) ?10-23 e-cm ? de(8.1
  ?11.6)?10-23 e-cm
• 10-30 e cm seems feasible!!!