Search for an Electric Dipole Moment of 199Hg

Blayne HeckelUniversity of Washington

Graduate students: Jennie Chen, Brent GranerScientific glassblower: Erik Lindahl

Support: NSF and DOE Low Energy Nuclear Physics

History of 199Hg EDM results

20142001 20091993 1995

Current sensitivity

LamoreauxJacobsKlipsteinFortson Griffith

SwallowsRomalisLoftusFortson

1.00E-30

1.00E-29

1.00E-28

1.00E-27

1.00E-26

1.00E-25

2 s

igm

a u

pp

er

lim

it

1987

wOT

wOB

BE

wMT

wMB

E Cancels up to 2nd order gradient noise

4-Cell, 199Hg Magnetometer

omc 3

1

dE

zz

Bc

4)

3

8( 3

3

3

EDM insensitive channels: ωOT - ωOB and (ωOT + ωOB) – (ωMT + ωMB) monitor for E field correlations odd and even in z, respectively.

EDM sensitive frequency combination

Cell Holding Vessel

Cell Holding Vessel

Schematic Overview

Vapor Cells

Pump

Probe

Improvements to the EDM Experiment

Vapor Cell development: Stable spin lifetimes of 800, 600, 500, and 270 secProblem of disappearance of Hg within the cells solved

Reduced magnetic field noise – less conducting materials near the cells

Light induced noise and systematic effects eliminated by precession in the dark

Reduced high voltage leakage currents:Measure separately the currents across the cell and to the ground plane

Commercial uv laser provides better stability

We are working on improving the beam pointing stability

Precession in the dark

Optical rotation angle of 240

Advantages: Longer spin coherence times Light induced noise and systematic errors eliminated Insensitive to common mode B field drift

A B

Frequency difference extractionBecause we are only interested in cell pair frequency differences during the light-off period, we need only the phase difference between cells at the end of the A period and start of the B period:

ABDark TT

AB

)()(

We find Δω by multiplying the signals from the 2 cells.

andtAetSFrom nt

nn )sin()( /

/2222 )2/()2/()()( ntnnnn eAtStStStN

andttNtStSgetwe nnnn )sin()(/)()( �

)cos(2/)]2/()2/([)( nnnn ttStStC���

)sin()()()()( nnMB

nMT

nMB

nMT ttStCtCtSFinally

����

ΔωMT-MB (mrad)

Photo-Diode (V)

2

4

6

8

10

Time (s)50 100 150 200 250

1.5

1.0

0.5

0

2.0

TA TB

ABDark TT

AB

)()(

Filtered Data

System Performance

Rad

/s

Run Number

Average angular frequency relative to first scan

This corresponds to a drift of ~1 µGauss/day

Rad

/sR

ad/s

Δω (MT-MB) Middle cell angular frequency difference

Δω (OT-OB) Outer cell angular frequency difference

0.3 nG/day

Rad

/sR

ad/s

Δω (OT-MT) + Δω (OB-MB) Quadratic field drift channel

ΔωC EDM sensitive frequency combination

80 pG/day

Rad

/s

ωedm(n) = (-1)n [ΔωC(n-1) - 2 ΔωC(n) + ΔωC(n+1)]/4

One day EDM signal

ωedm = xx ± 2.0 × 10-9 rad/s, a factor of 4 improvement over 2009

(3.5 × 10-29 e-cm/day for 10kV runs)

Data Sequences

EDM data is taken in ``sequences’’. Each sequence comprises:

• A defined set of cell orientations and ordering in the vessel• Equal number of day long runs at 6kV and 10kV• Equal number of runs with normal and reversed magnetic fields• Equal number of runs with fast and slow high voltage ramp rates• Typically 16 -20 runs total

We have completed 7 data sequences and have 5 to go for a complete EDM data set.

For seq. 1-6: at 10kV, dHg = -(13.4 ± 5.6) × 10-30 e-cm at 6kV, dHg = -(15.6 ± 9.3) × 10-30 e-cm

combined, dHg = -(14.0 ± 4.8) × 10-30 e-cm

(blind offset in place)

ωc

(rad

/sec

)

χ2 = 1.05

Sequence 1-6

ωc

(rad

/sec

)

χ2 = 1.02

Sequence 1-6

-25

-20

-15

-10

-5

0

5

10

15

20

EDM data by Sequence

Seq.3Seq.2 Seq.4 Seq.5 Seq.6Seq.1

10 kV χ2 = 1.22

ωc

× 1

0-10

rad/

s

-25

-20

-15

-10

-5

0

5

10

15

6 kV χ2 = 0.98

ω c

× 1

0-10

rad/

s

Seq.3Seq.2 Seq.4 Seq.5 Seq.6Seq.1

B field up

B field down

χ2

Systematic Uncertainties

2009 Error Budget

X (no sparks observed) X (precession in the dark)

-- Scale with frequency precision

IGas= 0.4 pA (2009)

ICell = 0.08 pA (2009)

10 kV

0 Volts

Leakage Currents

We now measure separately the currents flowing down the cell walls and through the dry air.

2014: With tin oxide coated ground planes (rather than gold), we see 10 times less leakage current -- no photo-electrons:Igas = 0.04 pA (2014), Icell = ?

Issues to address

• Better understanding of the long time constants associated with the leakage currents

• Identification of the dominant source of excess noise(simulated data with Gaussian photon shot noise added results in 40% smaller EDM values)

• Identification of the source for occasional runs with 2-3 sigmacorrelations between the outer cell frequency difference and high voltage

Summary

• We anticipate a 199Hg EDM result with a factor of roughly 4 improvement in statistical precision by the end of 2014.

• The data, so far, looks reasonable but there remains work to do concerning systematic errors.

• We are constructing shorter vapor cells to allow us to increase the applied electric field in our current EDM apparatus.

Laser System

SDL MOPA: 500 mW at 1015 nm

1st Doubler: 130 mW at 507 nm

2nd Doubler: 6 mW at 254 nm

Transverse Pumping / Optical Rotation

B

254 nm s+

Pump Phase

B

254 nm Linear

Probe Phase wL

Linear Polarizer

Detector

Pump

Probe

Probe

Optical Rotation Angle Absorption

Transverse Pumping / Optical Rotation

Typical 24 Hour Run

Final Dataset and Statistical Error

d(199Hg) = (0.49 ± 1.29stat )x10-29 e cm

0.1 nHz (~ 7.5 ppt)

Systematic Errors and Tests for Systematic Effects

No Statistically Significant Dependence on:• The Vapor Cells or Electrodes (or their orientation)• The DAQ Channel Ordering• The Vessels

99% of Total Error

Systematic Error Budget

Statistical Error 12.90

Bounds on CP Violating Parameters

d(199Hg) = (0.49 ± 1.29stat ± 0.76sys ) x 10-29 e cm

| d(199Hg) | < 3.1 x 10-29 e cm (95% CL)

Confidence Levels: 199Hg (95%), 205TI (90%), TIF (95%)

Quark Chromo EDMs

Proton EDM

Semi-Leptonic Interactions:

QCD Phase

Neutron EDM

Electron EDM

Current Status

• More uniform and stable magnetic field• Detection of both polarization states of transmitted light• ``In the Dark’’ elimination of uv light induced noise and systematic error

Six-fold Reduction of Noise

``In the Dark’’ Old Analysis

Current Status

Improved Hg Vapor Cells: so far, natural Hg test cells

• Hydroxy bonded rather than glued – should last forever• 600 sec spin lifetime (distilled wax + smaller magnetic field gradients)

Remaining Tasks: • Construct enriched Hg vapor cells• Acquire a new uv laser source

Summary

Our 2009 Result led to a New Limit on the EDM of 199Hg

| d(199Hg) | < 3.1 x 10-29 e cm (95% CL)

• Factor of 7 Reduction in Previous Upper Limit• Improved Bounds on CP Violating Parameters

• Expect Factor of 5 improvement in Experimental Sensitivity• Expect to begin data collection later this year

Upgrading the Current Apparatus

Among his many accomplishments, Norman Ramsey founded the research field of EDM measurements and developed many of the techniques needed to do such precise measurements. He will always be an inspiration to us.

Reasons to Expect more T (CP) Violation

• The observed matter-antimatter asymmetry: CP violation in the SM is too small to

account for Baryogenesis.• The Strong CP problem:

Why is QCD so small?• The Standard Model is incomplete:

Extensions to the SM, such as SUSY, introduce new phases that lead to new sources of CP violation often

106 times larger than the SM for EDMs.

From the 199Hg EDM to Models for CP Violation

199Hg Atomic EDM

Atomic Physics

199Hg Schiff Moment

Nuclear Physics

CP-Violating Pion-Nucleon Coupling

QCD

CP-Violating QCD Term, Quark Chromo-EDMs

Model-Dependent CP-Violating Parameters

SUSY, etc …

Contributions to S from p, n EDMs

d(n)d(p)

Hyperfine Coupling: d(e)

Semileptonic Interactions: CS CP CT

Naturalness Parameters

Constrained MSSM

Measuring an EDM via Larmor Precession

B

mwL

d

E