Philip Harris CryoEDM at ILL. P. Harris ORNL, 11 Oct 2012 Overview Motivation, history and technique CryoEDM: Current status Upgrade Systematic errors

Philip Harris

CryoEDM at ILL

P. HarrisORNL, 11 Oct 2012

Overview

Motivation, history and technique CryoEDM: Current status Upgrade Systematic errors Timeline Conclusion


CryoEDM Collaboration

C. Baker, S. Balashov, A. Cottle, V. Francis, P. Geltenbort, M. George, K. Green, M. van der Grinten, M. Hardiman, P. Harris, S. Henry, P. Iaydjiev, S. Ingleby, S. Ivanov, K. Katsika, A. Khazov, H. Kraus, A. Lynch, J.M. Pendlebury, M. Pipe, M. Raso-Barnett, D. Shiers, P. Smith, M. Tucker, I. Wardell, H. Yoshiki, D. Wark, D. van der Werf


Electric Dipole Moments

EDMs are P, T odd Complementary study of

CPv Constrains models of new

physics

E +


History

Factor 10every 8 yearson average


Measurement principle

() – () = – 4 E d/ h

with appropriate compensation for any changes in B during measurement period.

B0 E<Sz> = + h/2

<Sz> = - h/2

h(0) h() h()

B0 B0 E

Use NMR on ultracold neutrons in B, E fields.


Ramsey method of Separated Oscillating Fields

4.

3.

2.

1.

Free precession...

Apply /2 spin-flip pulse...

“Spin up” neutron...

Second /2 spin-flip pulse

130 s

2 s

2 s

29.7 29.8 29.9 30.0 30.1

10000

12000

14000

16000

18000

20000

22000

24000

xx

x = working pointsResonant freq.

xx

Spi

n-U

p N

eutr

on C

ount

s

Applied Frequency (Hz)


UCN production in liquid helium

1.03 meV (11 K) neutrons downscatter by emission of phonon in liquid helium at 0.5 K

Upscattering suppressed: Boltzmann factor e-E/kT means not many 11 K phonons present

Observed: C.A.Baker et al., Phys.Lett. A308 67-74 (2002)

n = 8.9 Å; E = 1.03 meV

Landau-Feynman dispersion curve for 4He excitations

Dispersion curve for free neutrons

R. Golub and J.M. Pendlebury Phys. Lett. 53A (1975), Phys. Lett. 62A (1977)


CryoEDM overviewNeutron beam input

Transfer section

Cryogenic Ramsey chamber


Sensitivity

•Successfully produced, transported, stored UCN, but need

to reduce losses

•Successfully produced, transported, stored UCN, but need

to reduce losses

•Successfully applied 10 kV/cm (same as previous expt); aiming for 20-30

kV/cm

•Successfully applied 10 kV/cm (same as previous expt); aiming for 20-30

kV/cm

•Achieved 60% polarisation in source,

but must improve

•Achieved 60% polarisation in source,

but must improve

•RT-edm: 130 s. So far we have 62 s cell storage

time.

•RT-edm: 130 s. So far we have 62 s cell storage

time.


Neutron numbers• Anticipated production rate 1.4 /cc/s• Aperture mask x 0.44• Entrance window scattering x 0.8• Beam attenuation x 0.72• Source storage lifetime 91 s• Incomplete source filling (200 s): x

0.89

Gives expected density in source: 30/ccSource volume 10.5 litres.


Neutron numbers• Measurement has been somewhat

indirect (neutrons taking convoluted paths to detectors) but it appears that we are currently down a factor of ~4: Under investigation

• Alignment/divergence issue?• Spectrum affected by upstream

instruments?


Neutron numbers• Guides and valves not yet optimal. • Ramsey chambers: first attempt

yielded storage time 60 s. For next time, improved cleaning; also bakeout.

• What is limiting storage lifetimes in source and cells...?


Electric field

See talk by M. Hardiman Latest feedthru installed designed

for 30 kV (6.7 kV/cm); it was run up to 45 kV (10 kV/cm).

We know how to design feed up to ~80 kV, and possibly up to ~150 kV, but...

... will need mild pressurisation of He.


Detectors Solid-state detectors

developed for use in LHe Thin surface film of 6LiF: n +

6Li + 3H; 82% efficient Fe layer for spin analysis Currently, peak hidden

under background pulse-shape discrimination

Now moving to detector with 10x area, to cover entire guide

C.A.Baker et al., NIM A487

511-520 (2002)


Detection of polarised UCN

Observed ~60% polarised downscattered neutrons Should be able to improve on this - Upcoming

measurement of source polarisation


T1

Longitudinal polarisation T1 is fairly straightforward to hold: field mustn’t change too fast for precession to follow

Issues last time with superconducting material around source/guide region...

Need to watch also sensitive area at entrance to shields, where field is low


T2 Transverse polarisation T2 is more delicate.

Depends largely on variation of Bz within trap volume – causes dephasing: goes as

We are aiming for ~1 nT across the bottle Currently in commissioning phase. SS

plates at end of superfluid containment vessel (SCV) distort field. Modelling suggests that with correction coils we can reach T2 ~ 30 s with current SCV.

Working on non-magnetic SCV.


Sensitivity summary: Current

Room-temperature expt final sensitivity ~2E-25 ecm/day Took 12 years of incremental developments from known

technology Systematics limited (geometric phase effect)

We can come within factor 4-5 of this in 2013 by increasing detector area x10: technology now proved refurbishing damaged detector-valve: in hand applying ~70 kV (previously ~40 kV): should be

straightforward opening beam aperture from 43 to 50 mm: depends on

radiation levels retaining polarisation: superconducting material has been

removed

There may be additional improvements beyond this peak above background (detector improvement) Polarisation to 60% or more (improved guide field) Increasing cell storage lifetime (insulator bakeout)

(we will achieve these by 2014)


Shutdown, move to new beamline

Mid-2013: Have to vacate current location. ILL to shut down for a year; we move to new dedicated beamline.New beam 4x more intense; and dedicatedDue to become operational mid-2014Beam must then be characterised (9A flux, divergence, stability, polarisation) We will then have access to the area (late 2014) to move our apparatus into it.


Upgrade 2013-15 Not yet fully costed Major upgrade to experiment:

Cryogenics design changes: Pressurise the liquid helium: increase E field x 2-3

Upgrade to back-to-back cells (or possibly 4 cells) 2 x neutrons Cancellation of some systematic effects

Installation of inner superconducting magnetic shield

B-field stability improves x500, for systematics Construction of non-magnetic SCV

Improves depolarisation: better T2 Overcome geometric-phase systematic error

Net result: Order of magnitude improvement in sensitivity Commensurate improvement in systematics


Systematics: General Systematics minimised by highly

symmetric data taking: B and E field reversals Alternating either side and

above/below middle of central Ramsey fringe

Upgrade: opposite E in adjacent cells Possibly also neutron magnetometers

in adjacent (outer) cells, for 4-cell system


Systematics: B field fluctuations At present, Pb shield too short: flux lines

clip coil end, inducing current in whole coil

Introduces common-mode noise, limiting sensitivity to 1E-27 e.cm

Figure: JMP


Systematics: B field fluctuations We plan to add an inner

superconducting shield. Scale model work in lab (MH) suggests that this can bring increased shielding factor ~500.

Figure: JMP

ISS


Systematics: B field fluctuations Can also (or instead) add Pb end caps,

calculated to give factor ~250 improvement

Figure: JMP

P. HarrisORNL, 11 Oct 2012Br

Br

Bnet

Bnet

Bv

Bv

Bv

Bnet

Bnet

... so particlesees additionalrotating field

Frequency shift E

Looks likean EDM, butscales withdB/dz

Bottle(top view)

Systematics: Geometric phase


Systematics: Geometric phase For neutrons,

Scales as 1/B2; increase B 5x to obtain factor 25 protection

<1 nT/m 3E-29 e.cm


Systematics: E x v

Translational: Vibrations may warm UCN, cause CM to rise

~1 mm in 300 s 3E-6 m/s If E, B misaligned 0.05 rad., gives 2E-29 e.cm

Rotational: Net rotation damped quickly (~1 s): matt walls Delay before NMR pulses allows rotation to die

away Neutrons enter E-field cells centred

horizontally; no preferred rotation Below 1E-29 e.cm


Systematics: 2nd order E x v

Perpendicular component, adds in quadrature to B.

Prop. to E2; gives signal if E reversal is asymmetric

Cancellations (back-to-back cells; B reversals) reduce effect to < 3E-29 e.cm


Systematics: metal hysterisis

Room-temp expt: Pickup in B coil from E field reversals; return flux causes hysterisis in metal

Coil here is SC, not power-supply driven

Inner shield is SC also Small effect from trim coils,

enhanced by any misalignments Net estimate < 1E-30 e.cm


Systematics: E induced cell movement

Electrostatic forces of order 1 N; E2

Asymmetry perhaps ~1% of this Radial gradients of order 3 nT/m Must keep radial displacement on E

reversal symmetric to ~ 0.01 m Cancellation with double cell Symmetric voltages to ~2% Net effect < 1E-28 e.cm


Systematics: Leakage currents

Azimuthal current components generate axial contributions to B

Cancellation in adjacent cells Conservative estimate: 1 nA 5E-

29 e.cm In reality LHe should keep currents

much below this? New source of current: ionisation

from UCN decay electrons (10-100 pA?, but preferentially axial)


Systematics: HV supply contamination

HV circuit isolated as far as possible to minimise earth contamination. Feedback line far from cells. Separate computer control.

10 kHz ripple on HV line can “pull” resonant freq. Estimate 1E-30 e.cm

Likewise 50 Hz ripple: estimate ~1E-29 e.cm

Directly generated AC B fields negligible


Systematics: Summary

Effect Size (e.cm)

B fluctuations 1 x 10-30

Geometric phase 3 x 10-29

Exv translational 2 x 10-29

Exv rotational 1 x 10-29

Exv 2nd order 3 x 10-29

metal hysterisis 1 x 10-30

E-induced cell movement 1 x 10-28

Leakage currents 5 x 10-29

HV line contamination 1 x 10-29


Sensitivity timelineDate Item factor ecm/year

Comment

2002RT-edm 1.7E-26 Baseline

2010CryoEDM commission 1.7E-24

2012Large-area detector 3.5 4.9E-25 Proven

2012HV to 70 kV 1.6 3.1E-25 OK to 50 kV, lab tests suggest should work at 70 kV

2012Repair detector valve 1.3 2.5E-25 Repair – should be fine

2012Polarisation 60% 1.5 1.7E-25 Seen in source. Should transfer ok to cells.

2012Aperture to 50 mm 1.2 1.4E-25 Will increase radiation levels slightly, but should be ok

2013Ramsey time to 60 s 1.8 7.7E-26 Requires change of SCV baseplates

2013See alpha peak 1.4 5.5E-26 Quite likely by 2012, but we do not count on it by then

2014New beam 2.0 2.7E-26 ILL produced this estimate

2014Recover missing input flux?

2.2 1.2E-26Depends on geometry match to new beam.

2014Improve cell storage lifetime to 100 s

1.5 8.3E-27Not guaranteed, but haven't yet tried most obvious solutions (e.g. bakeout), so improvement likely

2014Match aperture to beam

1.3 6.4E-27Likely

2015HV to 135 kV 1.9 3.3E-27 Requires pressurisation. Lab tests show this is realistic.

2015Four-cell system 1.4 2.3E-27 Guaranteed part of upgrade

2015Polarisation to 90% 1.5 1.6E-27 No known reason why not

2013-15 Inner supercond. shield Lab tests on scale model shows factor 500

2013-15 Cryogenics Included in upgrade

2013-15 Non-magnetic SCV Included in upgrade


New collaborators

Swansea is interested in joining us soon.

There is still plenty of room for new collaborators! Grants panel would like to see us recruiting from overseas.


Conclusions

• CryoEDM is now commissioning• New beamline 2014• Aim to start running ~2015• No “showstoppers” evident• Goal (for now) ~3E-27 e.cm• There’s still room on board!

Documents

Philip Harris CryoEDM at ILL. P. Harris ORNL, 11 Oct 2012 Overview Motivation, history and technique CryoEDM: Current status Upgrade Systematic errors