Measurement of the electrons electric dipole moment Mike Tarbutt - - PowerPoint PPT Presentation

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Measurement of the electrons electric dipole moment Mike Tarbutt - - PowerPoint PPT Presentation

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Measurement of the electrons electric dipole moment Mike Tarbutt Centre for Cold Matter, Imperial College London. Pier and Ocean , Mondrian University of Birmingham, 6 th March 2013 The electrons electric dipole moment (EDM, d e )

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Measurement of the electron’s electric dipole moment

Mike Tarbutt

Centre for Cold Matter, Imperial College London.

University of Birmingham, 6th March 2013

‘Pier and Ocean’ , Mondrian

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SLIDE 2

+

  • Spin

Edm

+

  • Spin

Edm

The electron’s electric dipole moment (EDM, de) T T CP

implies

Insufficient CP

Either de = 0, or T

10-24 10-22 10-26 10-28 10-30 10-32 10-34 10-36 Multi Higgs Left - Right MSSM f ~ 1 MSSM f ~ a/p Standard Model Predicted values for the electron edm de (e.cm)

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Measuring the EDM – spin precession

B E

Particle precessing in anti-parallel magnetic and electric fields

Measure change in precession rate when electric field direction is reversed

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Atom / Molecule Electric Field

E

Using atoms & molecules to measure de

Interaction energy = - de .Eeff Eeff = F P

Structure dependent, ~ 10 (Z/80)3 GV/cm Polarization factor

For more details, see E. A. Hinds, Physica Scripta T70, 34 (1997)

For a free electron in an applied field E, expect an interaction energy -de.E N.B. Analogous to interaction of magnetic dipole moment with a magnetic field, -m . B

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We use a molecule – YbF

Effective field, Eeff (GV/cm)

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Relevant energy levels in the YbF molecule

  • de Eeff

de Eeff X 2S+ (n = 0, N = 0)

  • 1

+1 F = 1 F = 0 170 MHz MF Electric Field

E

A 2P1/2 (n = 0, N = 0) 552 nm We measure the splitting 2deEeff between the MF = +1 and MF = -1 levels

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Measurement scheme – a spin interferometer

Pulsed YbF beam Pump A-X Q(0) F=1 Probe A-X Q(0) F=0 PMT

F=1 F=0

rf pulse

B

HV+ HV-

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Counts

B E E

Measuring the edm with the interferometer

Signal α cos2 [f/2] = cos2 [(mB B – de Eeff ) T / ћ]

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Modulate everything

±E ±B ±B ±rf2f ±rf1f ±rf2a ±rf1a ±laser f ±rff

spin interferometer

Signal 9 switches: 512 possible correlations

  • The EDM is the signal correlated with the sign of E.B
  • We study all the other 511 correlations in detail
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Result (2011)

  • de = (-2.4 ± 5.7stat ± 1.5syst) × 10-28 e.cm
  • | de | < 10.5 × 10-28 e.cm (90% confidence level)
  • 6194 measurements of the EDM, each derived from 4096 beam pulses
  • Each measurement takes 6 minutes

Nature 473, 493 (2011)

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F = 0 F = 1 rf E Stark-shifted hyperfine interval F = 0 F = 1 rf E Stark-shifted hyperfine interval rf detuning phase shift: ~100 nrad/Hz Imperfect E-reversal Changes detuning via Stark shift Phase correlated with E-direction

Correction to EDM: (5.5 ± 1.5) × 10-28 e.cm

Correcting a systematic error

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Effect Systematic uncertainty (10-28 e.cm) Electric field asymmetry 1.1 Electric potential asymmetry 0.1 Residual RF1 correlation 1.0 Geometric phase 0.03 Leakage currents 0.2 Shield magnetization 0.25 Motional magnetic field 0.0005

Systematic uncertainties

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Result

10-24 10-22 10-26 10-28 10-30 10-32 10-34 10-36 Multi Higgs Left - Right MSSM f ~ 1 MSSM f ~ a/p Standard Model Predicted values for the electron edm de (e.cm)

| de | < 10.5 × 10-28 e.cm (90% confidence) Excluded region

(5 × 10-19 Debye)

de = (-2.4 ± 5.7stat ± 1.5syst) × 10-28 e.cm

Improvements planned to explore this region

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How to do better

The statistical uncertainty scales as:

1 N 1 T 1 E

Total number of participating molecules Coherence time Electric field

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Our dream experiment

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Cryogenic source of YbF

  • Produce YbF molecules by ablation of Yb/AlF3 target into a cold helium buffer gas
  • Helium is pumped away using charcoal cryo-sorbs
  • Produces intense, cold, slow-moving beams
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Cold, slow beam of YbF molecules

  • Rotational temperature: 4 ± 1 K
  • Translational temperature: 4 ± 1 K

Speed vs helium flow

Molecules / steradian / pulse Flow rate / sccm

Flux vs helium flow

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Magnetic guide

  • Permanent magnets in octupole geometry, depth of 0.6 T
  • Separates YbF molecules from helium beam
  • Guides 6.5% of the distribution exiting the source
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Laser cooling

  • Laser cooling is the key step!!

Laser Laser Ground state Excited state Absorption Spontaneous emission

v’’= 0 v’= 0 v’’=1 v’’=2

X2S(N=1) A2P½

552 nm 584 nm 568 nm 92.8% 6.9% 0.3%

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Simulations for YbF in an optical molasses

6 beams each containing 12 frequencies from 3 separate lasers – 750 mW total

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Sensitivity of an EDM fountain experiment

Quantity Value How determined? Molecules in cell 1013 Measured by us Extraction efficiency 0.5 % Measured by Doyle group Fraction in relevant rotational state 24 % Boltzmann distribution Fraction accepted by guide 6.5 % Magnetic guide simulation Fraction cooled in molasses 0.76 % Molasses simulation Rotational state transfer efficiency 100 % Pi-pulse Fraction though fountain 7.5 % Free-expansion at 185mK Detection efficiency 100 % Fluorescence on closed transition Coherence time 0.25 s By design Repetition rate 2 Hz By design EDM sensitivity in 8 hours 6 x 10-31 e.cm Statistical sensitivity

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Thanks...

Joe Smallman Jack Devlin Dhiren Kara Sarah Skoff Nick Bulleid Rich Hendricks Thom Wall Aki Matsushima Valentina Zhelyazhkova Anne Cournol

Jony Hudson Ben Sauer Ed Hinds