1. CryoEDM at ILL
Philip Harris

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

3. 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

4. Electric Dipole Moments
EDMs are P, T odd
Complementary study of CPv
Constrains models of new physics + E

5. History
Factor 10
every 8 years
on average

6. Measurement principle
Use NMR on ultracold neutrons in B, E fields. B0 B0 E B0 E
<Sz> = + h/2
h(0)
h()
h()
<Sz> = - h/2
() – () = – 4 E d/ h
with appropriate compensation for any changes in B during measurement period.

7. Ramsey method of Separated Oscillating Fields
“Spin up” neutron... 1.
2 s
Apply /2 spin-flip pulse... 2.
130 s
Free precession... 3.
2 s 4.
Second /2 spin-flip pulse

8. UCN production in liquid helium
ln = 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)
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. A (2002)

9. UCN production rate vs ln
Single-phonon production
Multiphonon production
1.190.18 UCN cm-3 s-1 expected, 0.91 0.13 observed
C.A.Baker et al., Phys.Lett. A (2002)

10. CryoEDM overview Neutron beam input Cryogenic Ramsey chamber
Transfer section

11. Sensitivity Achieved 60% polarisation in source, but must improve
Successfully produced, transported, stored UCN, but need to reduce losses
Successfully applied 10 kV/cm (same as previous expt); aiming for kV/cm
RT-edm: 130 s. So far we have 62 s cell storage time.

12. 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/cc
Source volume 10.5 litres.

13. 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?

14. 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...?

15. 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.

16. Detectors Solid-state detectors developed for use in LHe
Thin surface film of 6LiF: n + 6Li  a + 3H; 82% efficient
Fe layer for spin analysis
Currently, a peak hidden under g background
pulse-shape discrimination
Now moving to detector with 10x area, to cover entire guide
C.A.Baker et al., NIM A (2002)

17. Detection of polarised UCN
Observed ~60% polarised downscattered neutrons
Should be able to improve on this - Upcoming measurement of source polarisation

18. 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

19. 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.

20. 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
a 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)
new beam – pol to 90%. Cell storage lifetime

21. 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 dedicated
Due to become operational mid-2014
Beam 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.

22. 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

23. 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

24. 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

25. 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.
ISS
Figure: JMP

26. Systematics: B field fluctuations
Can also (or instead) add Pb end caps, calculated to give factor ~250 improvement
Figure: JMP

27. Systematics: Geometric phase
Bnet Br
Bnet
... so particle
sees additional
rotating field Bv
Bottle
(top view)
Frequency shift
 E
Looks like
an EDM, but
scales with
dB/dz

28. Systematics: Geometric phase
For neutrons,
Scales as 1/B2; increase B 5x to obtain factor 25 protection
<1 nT/m  3E-29 e.cm

29. Systematics: E x v Translational: Rotational:
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

30. 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

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

32. 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 mm
Cancellation with double cell
Symmetric voltages to ~2%
Net effect < 1E-28 e.cm

33. 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 ( pA?, but preferentially axial)

34. 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

35. 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
m metal hysterisis
E-induced cell movement
1 x 10-28
Leakage currents
5 x 10-29
HV line contamination

36. Sensitivity timeline 2002 RT-edm 1.7E-26 Baseline 2010
Date
Item
factor
ecm/year
Comment
2002
RT-edm
1.7E-26
Baseline
2010
CryoEDM commission
1.7E-24
2012
Large-area detector
3.5
4.9E-25
Proven
HV to 70 kV
1.6
3.1E-25
OK to 50 kV, lab tests suggest should work at 70 kV
Repair detector valve
1.3
2.5E-25
Repair – should be fine
Polarisation 60%
1.5
1.7E-25
Seen in source. Should transfer ok to cells.
Aperture to 50 mm
1.2
1.4E-25
Will increase radiation levels slightly, but should be ok
2013
Ramsey time to 60 s
1.8
7.7E-26
Requires change of SCV baseplates
See alpha peak
1.4
5.5E-26
Quite likely by 2012, but we do not count on it by then
2014
New beam
2.0
2.7E-26
ILL produced this estimate
Recover missing input flux?
2.2
1.2E-26
Depends on geometry match to new beam.
Improve cell storage lifetime to 100 s
8.3E-27
Not guaranteed, but haven't yet tried most obvious solutions (e.g. bakeout), so improvement likely
Match aperture to beam
6.4E-27
Likely
2015
HV to 135 kV
1.9
3.3E-27
Requires pressurisation. Lab tests show this is realistic.
Four-cell system
2.3E-27
Guaranteed part of upgrade
Polarisation to 90%
1.6E-27
No known reason why not
Inner supercond. shield
Lab tests on scale model shows factor 500
Cryogenics
Included in upgrade
Non-magnetic SCV

37. 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.

38. 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!