DOE 2/11/05 #1

EDM R&D Progress

Steve Lamoreaux, Los AlamosCo-spokesperson for the EDM Project

for presentation to The Department of EnergyCost & Schedule Review

Feb. 11, 2005

Electric Dipole Moment of the Neutron:10-28 e·cm in Superfluid He

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Overview

We are developing a new experimental technique to search for the neutron electric dipole moment (EDM) that offers a factor of at least 50 increase in sensitivity over existing experiments when operated at LANSCE (500 fold increase at SNS)

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Collaborating Institutions

• Hahn-Meitner Institut, Berlin• NIST/Gaithersburg• Harvard• Simon Fraser University• Caltech• University of Illinois• Los Alamos National Laboratory• Berkeley• Duke• Oak Ridge National Laboratory• University of Leiden• University of New Mexico• North Carolina

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Definition of the EDM

• A permanent EDM d: separation of the charged constituents of the neutron

• The current experimental technique (ILL) will likely yield d< 5•10-26e•cm

• We hope to obtain roughly < 10-28e•cm with UCN stored in superfluid 4He

+-s = 1/2d•E

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Evolution of Experiments

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Motivation:

To Elucidate the Nature of Time Reversal Asymmetry

• Physics Beyond the Standard Model: CP violation is phenomenologically introduced at present, based on K0 decay parameters. New sources of CP violation in B decay must be interpreted in background of usual CP violation

• Supersymmetry• Big Bang Baryogenesis: A new source of CP

violation is required to explain the observed matter-antimatter asymmetry in the Universe

• QCD Parameter (10-9 by present limits)Motivation for Axion searches

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Supersymmetry

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Physics Beyond the Standard Model

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The Basic Technique

+-

E

s = 1/2 dipole moment dn

Look for a precessionfrequency fn=gB ± 2dE

B

10-25 e cm in a 10 kV/cm electric field corresponds to a shift in frequency of 0.5 Hz

DOE 2/11/05 #10

ILL Experiment

1 UCN/cc10 kV/cm100 sec store2 x 10-26 e cm

199Hg Co-magnetometer—Systematic control

A new systematic“geometric phase” effect was found in this work (controllable at the 10-28 e cm level for our experiment)

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Competition: New ILL Experiment

Funded by PPRP for construction

Also work at PSI—not considered competitive

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Figure of Merit for EDM Experiments

x 180 when operated at LANSCE

NE

E 5E 5 N 200-2000 N

By performing the experiment directly in superfluid helium-4 (dielectric properties + superthermal production) that is doped with polarized helium-3 which serves as a magnetometer and spin precession analyzer

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Superthermal Source of UCN

Uw = 200 neVULHe = 20 neV

Quasi two-levelsystem with singlephonon upscatteringsuppressed by a smallBoltzmann factor.

up ~ 100 T-7 from 2-

phonon upscattering

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Liftime in a Storage Cell

Goal: 500 seconds 0.5 cc/sec production rate at LANSCE

holeup3wn

111111

w h e r e n i s t h e n e u t r o n l i f e t i m e ,

w i s t h e w a l l l i f e t i m e ,

3 i s a b s o r p t i o n l i f e t i m e ,

u p i s u p s c a t t e r i n g l i f e t i m e .

h o l e i s h o l e l i f e t i m e .

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Our Proposed Experiment

Light guides

PhotomultipliersMagnetic shield

Vacuum enclosure

Superconducting shield

HV variable capacitor

HV electrode

Ground electrodes

Neutron beam

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3He Magnetometry

dn dipole moment d3 =0

Look for a difference in precessionfrequency fn-f3=(n-3)B ± 2dE dependent on Eand correct for temporal changes in B0 by f3

-

EB EB

s = 1/2

n 3He

fn=nB ± 2dE f3=3B

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Co-Magnetometer

3He + n t + p (parallel) < 102 b(opposite) ~ 104 b

UCN loss rate ~1-p3•pn = 1-p3pn cos[(n-3 )B0 +2dE]t|n-3| = |n|/10 --- Sensitivity to static magnetic fields isreduced by an order of magnitude!!!

3He concentration must be adjusted to keep the lifetime reasonable for a given value of the 3He polarization.

The proper value for the fractional concentration x =Atoms-3He/Atoms-4He ~ 10-10.

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Light Detection

3

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Role of SQUIDs

SQUIDs M. Espy, A. Matlachov ~100 cm2 superconducting pickup coilFlux = 2 x 10-16 Tm2 = 0.1 0 Noise = 4 m0/Hz1/2 at 10Hz ~ T1/2

Although sensitivity to changing magnetic fields is reduced by a factor of 10, we can do better.Monitor 3He precession to get volume average of the magnetic field; eliminate (gn-g3)B0t term to high precision

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Low Field NMR (LANL)

•Recent progress in P-21 demonstrates SQUID-based NMR in fields of ~ 100 mG

•Data shown for natural polarization of protons in water pre-polarized in a 50 G field.

•System uses the same tangential gradiometer proposed for EDM experiment

•Noise 80 pG/sqrt(Hz), SQUID performance well characterized

•Gradiometer design will minimize effects of vibration and coupling of holding fields

•We have developed electronics allowing SQUIDs to survive pulsed fields for NMR

•Magnetic fields proposed for EDM are ~ 3 mG ; 3He precession ~10 Hz

3He precession frequency

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Low Field NMR (LANL)

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Operation of Experiment

• Fill cell with superfluid helium, doped with freshly polarized 3He

• Accumulate UCN by downscattering appropriately polarized cold neutrons for about 1000 sec while ramping up HV

• Flip spins 90o to B0 by RF pulses

• Observe scintillation signal and SQUID signal as a function of time for 1000 sec

• Ramp HV to zero, drain cell of spent 3He

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3He Atomic Beam Polarizer (LANL)

Final testing is in progress

Expected flux detected

Average velocity < 100 m/s

Polarization measurementsare consistent with the 100% expectation

Differential pump stages will be added soon, final tests will be completed

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Other Technical Achievements

•The diffusion of helium-3 in superfluid helium-4 has been measured and characterized; this is an important parameter for controlling the geometric phase systematic•Ultracold Neutrons were produced at LANSCE by scattering cold neutrons in superfluid helium; 180 second cell lifetime was due to the superfluid fill hole. Production rate extrapolated to improved moderator, higher target current, better guides is 0.5/cc/sec, implying 250/cc UCN density at FP12 of LANSCE•A helium isotopic purification apparatus has been operated•A realistic technical scheme for operating the experiment has been developed•We have acquired and operated a dilution refrigerator

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Gravitational Shift

Due to difference in the effective temperature of the UCN and3He atoms, there can be a displacement between the centers-of–gravity; this places a constraint on systematic magnetic field gradients

kThgnmh

3

2

This is 1.5 mm for UCN, for h=10cm and T=5mK – Systematic magnetic gradient must be less than 10 pG/cm for 10-28 e cm– 1 nA leakage (1/4 loop) gives a possible systematic of 5 x 10-29 e cm

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Electric Field Systematic Effects

sys EvB

0/2)γv(

31 fEsysf 3.0δ requires cm2810 E/Ee

For atoms contained in a cell, 0v

However, the effective field adds in quadrature with the applied static magnetic field. The net effect depends on the time between wall collisions, but in the case where there are many precessions between wall collisions,

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Gradient interference with E x v field

/

/

0

2

0r

r

B

cEaRBB

arBr Radial gradient

v x E fieldChanges sign withdirection

c

EaR 22

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Monte Carlo calculation of shift

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Magnetic gradient requirements

10-28 e cm requires a< 10 G/m

G/cm easy to achieve

Use gravitational offset to tune gradient to zero:

HznGmGmdzhdBz 3010/1010/ 3

10 Hz Larmor frequency implies 3 ppm differencein ratio of magnetic moments at maximum allowed gradient. The effect changes sign with direction of B0.

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Pseudomagnetic Field

• The polarized 3He creates an effective magnetic field for the UCN, corresponding to a Larmor frequency of about 1 mHz

• The anticipated sensitivity per cycle is about 1 Hz• In order to eliminate this potential noise source, the spin flip must be

controlled with an accuracy of 0.1%

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Purification of 3He

• The McClintock heat flush technique requires that the superfluid helium be above 1 K

• The per cycle heat energy is too high to bring the 10 liters that must purified to this temperature, then back to 0.3 K

• There is a narrow temperature window where the propagation of 3He atoms in the superfluid is sufficiently close to ballistic while there is a sufficient population with velocity sufficiently high to evaporate from the bath (2.8 K binding energy). The range is 0.3 to 0.4 K

• By using a charcoal pump over a large surface area “vat,” the 3He atoms can be pumped away on a time scale comparable to the experiment cycle time.

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Dressed Spins

• By applying a strong non-resonant RF field, the spins can be modified or “dressed”

• For a particular value of the dressing field, the neutron and 3He magnetic moments are equal

• This is an ideal situation: one simply tunes the dressing parameter until the relative precession is zero, and determines how this parameter changes as a function of electric field direction

• There are a number of difficult technical issues that need to be address, which includes gradients of the RF field and eddy currents

DOE 2/11/05 #33

Principle of Dressed Spin

)/(' rfrfo BJ

n 1.13

'' 3 n 1.1/ rfrfnB when

We want Brf >> B0 (1-10 mG) so Brf is around 1 G,rf /2 near 3 kHz

RF field must be homogeneous at the 0.1-1% level

Heating and gradients due to eddy currents present design challenges

Eliminates need for SQUID magnetometers and potentially increasesthe sensitivity of the experiment

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Conclusion

• We believe that the systematic effects can be controlled at a level sufficient to achieve a measurement accuracy of 10-28 e cm

• Many of the technical issues have been studied, many remain

• Achieving this level of sensitivity would severely constrain most, if not eliminate all, supersymmetric extensions to the Standard Model

• The presence of a co-magnetometer is absolutely essential to achieve this level of accuracy