1

Dressed Spin Studies with Polarized 3He

Andrea Esler & Jen-Chieh Peng (UIUC)

Steve Lamoreaux & Chen-Yu Liu (LANL)

2

Dressed Spin

Strong RF fields change the effective magnetic moments of neutrons and 3He

• First 3He spin dressing measurements performed in April 2005

• Change of 3He Larmor frequency with a dressing field has been observed.

In the B0<<B1 limit, the g factor modification has a simple formula

0 1/ ( / )dressed freeg g J B

3

Dressed Neutron Spin already observed

Effective g factor vs. RF field strength:

Numerical simulations reproduced these

results

Muskat, PRL 58(20), 1987

Fits the J0(B1/) prediction

4

Critical dressing equalizes precession rates

Crossing points equalize neutron and 3He g

factors:

Heneutron 3

3 1n 1n 0 3 0

0 0

BBJ J

J x J x

1.1127

3Heneutron

n 1 /x B

Effective dressed g factors:

• Reduce the effect of B0 [instability] on the two species

• A check of n=3: scintillation no longer modulated

5

4 m

1 K cold headInjection nozzle

Quadrupoleseparator

Spin flip region

Quadrupoleanalyzer

3Hedetector

Solenoid field 8 Gauss

B1 rf

Spin polarizer Spin analyzer

3He detector

RGA

90 cm

Experiment

Polarized 3He Source

6

Ramsey experiment technique (SOF)

When the RF pulses are applied on resonance (at the Larmor frequency) the 3He spin direction is completely reversed (minimal transmission)

Incoming 3He

/2 pulse

Free precessio

n

Second /2

pulseZ component

of nuclear spin

Images courtesy Sussex Neutron

EDM group

Analyzer & Counter-1

+1

accepts P=+1 state

Adding an RF dressing field slows down spin precession between the flip coils (or speeds it up…) & changes the minimum transmission frequency

7

3He experiment setup

source

to analyzer and RGA detector

solenoid

polarizer

Ramsey coils and dressing coils are

inside the solenoid

8

Spin-flip magnetic field B1 x distance

RG

A p

ressu

re r

ead

ing Full beam

transmission

Unpolarized

transmission

” pulse” field

setting

(5.9 4.0)2 95%

(4.0 0.01)P

Dec. 2004: P=99.6% was measured with better

shielding

3He beam polarization: P > 95%

9

vL

dBNP

eff /

)cos()( 1

• Polarization (as fn. of B1) averages over 3He velocities

• P(B1) measures Fourier cosine transform of velocity spectrum

• Invert the FT to measure N(v):

Img. courtesy S. Lamoreaux

1 K “Maxwell” dist.

Accepted velocities

From Dec. 2004 meeting:

Velocity spectrum

deduced from April

measurements needs to be

calibrated, but we expect agreement

10

open and closed shutter

the same, log scale

6 nTorr

0.01 nTorr

3He beam background pressure

11

Mapping the dressing field

Dressing magnet coil

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Dressing coil field map

Average field: 1.6 Gauss / Ampere

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3He dressed spin results I

Minimal transmission rate observed at the 3He Larmor precession frequency

Incr

easi

ng

dre

ssin

g

field

Dressing field frequency 43.5 kHz

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3He Larmor Freq. Dressed at 43.5 kHz

Max B field

5.8 G

04.1%f

f

Inconsistent with simple formula; B0~B1

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43.5 kHz data vs. simulation

3He Larmor frequency vs. dressing field

26.2

26.4

26.6

26.8

27

27.2

27.4

27.6

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Dressing field magnitude [G]

Lar

mo

r fr

equ

ency

[kH

z]

LANL data

Simulation

Rough agreement with Bloch-equation simulations – I am working to refine the code

16

3He dressed spin results IIIn

creasi

ng

dre

ssin

g

field

Dressing field frequency 8.1 kHz

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3He Larmor Freq. Dressed at 8.1 kHz

Max B field

1.6 G

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Outlook

• Continue analysis– Understand observed Larmor freq. behavior

• Upcoming measurements (this week) will emulate EDM experimental conditions– More intense dressing fields over smaller

volume (new coils already built)– Smaller B0 (limited by earth’s field ~5 G)– Larger dressing field frequency ~50-100 kHz