The cryogenic neutron EDM experiment at ILL

and the result of the room temperature experiment

James Karamath

University of Sussex

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In this talk…

(n)EDM motivation & principles

Room-temperature nEDM experiment at ILL

Systematics

CryoEDM

Summary

James Karamath University of Sussex 18/04/23 10:06 PM

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(n)EDMs – so? I

P- and T-violating

CPV in SM not fully understood e.g. insufficient CPV for baryon asymmetry

Strong CP problem θCP < 10-10 rad. Axions?

James Karamath University of Sussex 18/04/23 10:06 PM

n n

p

×

S+

-d

S

-

+

d

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(n)EDMs – so? II

Estimated EDMs model dependent SM dn ~ 10-31 ecm Other models typically 105-6 times greater

e.g. SUSY: CP < 10-2

quark electric dipole moments: q q

gaugino

squark

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nEDM measurement principle

B0 E<Sz> = + h/2

<Sz> = - h/2

h(0) = -2μ.B h()=2(-μ.B+dn.E)

h()=2(-μ.B-dn.E)

B0 B0 E

dn defined +ve

↑↑ - ↑↓= Δ = 4dn.E / h

Ramsey NMR performed on stored Ultra Cold Neutrons (UCN)

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nEDM statistical limit

Fundamental statistical limit

α = visibility [polarisation product]E = E-field strengthT = NMR coherence timeN = total # counted

NET

dn

2

~10-26ecm

James Karamath University of Sussex 18/04/23 10:06 PM

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nEDM systematic limit

Main concern: changes in B-field accidentally correlated with E-field changes give false dn signal

h(ν↑↑–ν ↑↓) = 2|μn|(B↑↑–B↑↓) – 4dnE

True nEDM signal

False signal due to varying B

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nEDM experiments: history

Co-magnetometer era

Cryogenic UCN era

RT stored UCN era

NET

hdn

2

Beam eraΔB ≈ v x E / c2 limited

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Current nEDM experiment at ILL I

Create UCN, can then be guided & stored

Polarise UCN

UCN admitted into cell with E and B-fields and stored…

Mercury polarised by Hg lamp and added to cell

N S

Storage cell

Magnet & polarizing foil / analysing foil

UCN

Approx scale 1 m

BE

Magnetic field coil

High voltage lead

James Karamath University of Sussex 18/04/23 10:06 PM

Magnetic shielding

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Current nEDM experiment at ILL I

Ramsey NMR performed

Released from cell Neutrons spin

analysed (# fn of precession)

Repeat: E=↓or 0, B=↓ N S

Magnetic shielding

Storage cell

UCN detector

Approx scale 1 m

Magnetic field coil

B

High voltage lead

E

Magnet & polarizing foil / analysing foil

James Karamath University of Sussex 18/04/23 10:06 PM

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Current nEDM experiment at ILL II

HV in

B0 field coils

Ground electrode

Neutron cell

Mercury lamp light *

Neutrons in/out

*

Mu-metal B-shields

James Karamath University of Sussex 18/04/23 10:06 PM

Z

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Systematics I

Reminder: B-field shifts correlated with E-field changes constitute false dn signal.

Protect against incoming perturbations with mu-metal shields

Measure changes IN cell with Mercury Cohabiting Magnetometer…

James Karamath University of Sussex 18/04/23 10:06 PM

h(ν↑↑–ν ↑↓) = 2|μn|(B↑↑–B↑↓) – 4dnE

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Systematics II

Hg EDM known to be below ~ 10-28 ecm.

Thus variations in mercury NMR signal are due to B-field fluctuations…

Cohabiting Mercury Magnetometer

James Karamath University of Sussex 18/04/23 10:06 PM

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Co-magnetometer correction

0 5 10 15 20 2529.9260

29.9265

29.9270

29.9275

29.9280

29.9285

29.9290

29.9295

Ne

utr

on

re

son

an

t fr

eq

ue

ncy

(H

z)

Run duration (hours)

Electric Field

+-

Systematics III

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Co-magnetometer correction

0 5 10 15 20

7.7882

7.7884

7.7886

7.7888

7.7890

Run duration (hours)

Mer

cury

fre

quen

cy (

Hz)

Systematics III

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Co-magnetometer correctionSystematics III

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Systematics IV

However, not perfect correctionMercury fills cell uniformly, UCN sag under

gravity, lower by ~3 mm.

Thus don’t sample EXACTLY the same B-field. Axial (z) gradients → problems…

Magnetometer problems

Hg n

z

James Karamath University of Sussex 18/04/23 10:06 PM

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Systematics V

Two conspiring effects v x E: motional particle in electric field

experiences B-field: ΔB ≈ v x E / c2

Axial field gradient dB/dz creates radial B-field (since .B=0) proportional to r, Br r

Let’s look at motion of a mercury atom across the storage cell

Geometric Phase Effect (GPE)

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Systematics VI Geometric Phase Effect (GPE)

dB/dz → B r

B v x E Scales with E

like EDM!!!

Scales with dB/dz

(GPEHg ~ 40GPEn)

Resultant

i.e. B0 field into page has gradient

Shifts resonance of particle

Using Mercury

introduces error

E and B0 into page

Rotating B field

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Systematics VII Other

Effect Shift Uncertainty

Statistical 0 1.51Door cavity dipole; quadrupole fields -1.10 0.45Other GP dipole shifts 0 0.60(E x v)/c2 from translation 0 0.05(E x v)/c2 from rotation 0 0.10Light shift: direct & GP 0.35 0.08B fluctuations 0 0.24E forces – distortion of bottle 0 0.04Tangential leakage currents 0 0.01AC B fields from HV ripple 0 0.001Hg atom EDM 0 0.052nd order Exv 0 0.002

Total –0.75 1.51 stat, 0.80 sys

GPE: J Pendlebury et al., Phys Rev A 70 032102, 2004

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Final result

Room temperature experiment complete!Soon to be published result (PRL):

dn = (+0.61.5(stat) 0.8(syst)) x 10-26) ecm

i.e. |dn| < 3.0 x 10-26 ecm (90% CL)

New cryogenic experiment will eventually

be x100 more sensitive…

hep-ex/0602020 www.neutronedm.org

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The cryogenic nEDM experiment

Reminder: NET

dn

2

RT Cryo

N /day 6x106 ~6x108

T /s ~130 ~250

0.75 ~0.9

E /kV/cm ~12 ~50

(B0 /μT 1 5)

~10-28ecm

*

*with new beamline

x20 x5*

x2

x1.2

x4

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Improved production of UCN (↑N) I

Crosses at 0.89nm for free (cold) n. Neutron loses all energy by phonon emission → UCN.

Reverse suppressed by Boltzmann factor, He-II is at 0.5K, no 12K phonons.

Dispersion curves for He-II and free neutrons

James Karamath University of Sussex 18/04/23 10:06 PM

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Improved production of UCN (↑N) II

Idea by Pendlebury and Golub in 1970’s, experimentally verified in 2002 (detected in He-II) for cold neutron beam at ILL (~1 UCN/cm3/sec).

Also better guides – smoother & better neutron holding surfaces, Be / BeO / DLC → more neutrons guided/stored. Allows longer T too.

James Karamath University of Sussex 18/04/23 10:06 PM

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Polarisation and detection (α) I

Polarisation by Si-Fe multi-layer polarizer, 95±6% initial polarisation.

Could lose polarisation in 2 ways: “Wall losses” magnetic impurities in walls,

generally not aligned with neutron spin Gradients in B-field, if not smooth and steady

have similar effect

James Karamath University of Sussex 18/04/23 10:06 PM

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Polarisation and detection (α) II

Detector: solid state, works in 0.5K He-II.

n (6Li, α) 3H reaction - alpha and triton detected

Thin, polarised Fe layer - spin analysis

James Karamath University of Sussex 18/04/23 10:06 PM

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Improving the E-field (↑E) I

He-II has high dielectric strength .

However, many questions to study; Nature of breakdown e.g. area/volume effects,

purity effects…

Flow of current in/along surfaces in He-II

Effect on system of ~J energy breakdown in He-II (e.g. on electrode coatings, gas evolution) etc…

James Karamath University of Sussex 18/04/23 10:06 PM

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Improving the E-field (↑E) II

Test electrodes submerged in He-II in bath cryostat.

Studying Vmax and Ileak as function of d, T, dielectric spacers, purity… up to 130 kV.

Some similar(ish) past data but varied results.

E

±HV

cryostat

He-II (T, purity…)

gap (d, V, spacers)

Sussex HV tests

~20cm

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Improving the E-field (↑E) IIIPast

literature

1

10

100

1000

0.0001 0.001 0.01 0.1 1 10

Electrode separation /cm

Bre

akd

ow

n V

olt

age

/kV

He-I data

4.2<T(K)<2.2

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Improving the E-field (↑E) IIIPast

literature

1

10

100

1000

0.0001 0.001 0.01 0.1 1 10

Electrode separation /cm

Bre

akd

ow

n V

olt

ag

e /kV

He-II data

2.2<T(K)<1.4

0.5K

1.8-2.1K

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Improving the E-field (↑E) IV

Now have a 400 kV supply to connect to HV electrode.

Will sit in 3bar SF6.

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Magnetic field issues I

Target – need ~ 100 fT stability (NMR)Need ~ 1 nT/m spatial homogeneity (GPE)Perturbations ~ 0.1 μT (buses!)Need (axial) shielding factor ~ 106

Mu-metal shielding ~ 12 Superconducting shielding ~ 8x105

Active shielding (feedback coils) ~ 15

Shielding factors

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Magnetic field issues II

CRYOGENIC nEDM! Utilise superconducting shield and B0 solenoid. Major part of fluctuations across whole chamber

(common mode variations) Magnetometer (zero E-field) cells see same

Very stable B0(t) current

Holding field x5 to reduce GPE in the neutrons by factor of 25 (GPEn 1/B0

2)

Extra benefits

James Karamath University of Sussex 18/04/23 10:06 PM

E

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Magnetic field issues III

~fT sensitivity 12 pickup loops will

sit behind grounded electrodes.

Will show temporal stability of B-field at this level.

Additional sensitivity from zero-field cell(s)

SQUIDS

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And so, the cryo-nEDM experiment I

n guide tubes + spin analyser

E ~ 60kV/cm

E = 0kV/cmSpin flipper coil (measure other spin)

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And so, the cryo-nEDM experiment II

HV electrode

Ground electrodes

HV in

z

Carbon fibre

support

BeO spacers

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And so, the cryo-nEDM experiment III

HV electrode

Ground electrodes

G10 Superfluid

containment vessel

HV in

z Neutrons in/out

250l He-II 0.5K

**

* BeO spacers/guides

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And so, the cryo-nEDM experiment IV

1m

Dynamic shielding coils

Magnetic (mu-metal) shields

Superconducting shield and solenoid

The shielded region

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Schedule / Future

Finish construction THIS SUMMERStart data taking THIS AUTUMNFirst results ~2008/9Upgrade neutron guide to ↑N ~2009 ?

James Karamath University of Sussex 18/04/23 10:06 PM

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Summary

(n)EDMs help study T-violation and are constraining new physics.

Systematics of RT-nEDM experiment well understood.

Final RT result: |dn| < 3.0 x 10-26 ecm.

Cryo-nEDM project starts this Autumn, 2008/9 brings ~ mid 10-28ecm results. New beamline for low 10-28ecm.

hep-ex/0602020 (RT result) www.neutronedm.org

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Done!

Thanks for listening