1. EDM Experiments: UK interests
Philip Harris
PPAP meeting 22nd July 2014

2. Electric Dipole Moments+
EDMs are P, T odd
Complementary study of CPv: must test elsewhere than K, B
Strong CP problem
Constrains models of new physics
SUSY CP problem
Baryon asymmetry
SM CPv inadequate
New models bring larger EDMs
Clean system – background free n g p
p  × q g
gaugino
squark

3. LHC and SUSY LHC excludes NP scenarios 100 GeV-1 TeV
This solves “old” SUSY-CP problem of EDM constraints on CPv phases by raising MSUSY, but moves away from “naturalness” argument that msquark should be near to weak scale
High mH also makes NMSSM models interesting. These often have EDMs at 2 loops... Constraints already tight; limit CP-odd H decays.
Still need viable baryogenesis mechanism. Essential to look at other CPv channels
See e.g. McKeen, Pospelov, Ritz,

4. nEDM History
Factor 10
per decade
on average
... but slowing

5. Sensitivity a <= 1 T <= few hundred s
E can be high in strong dielectric – LHe
N high in superthermal (LHe) source
Universal agreement that ultimate
sensitivity will almost certainly
come from a cryogenic experiment.

6. CryoEDM 10-year effort But...
Demonstrated superthermal n production at expected rate
Up to 65% polarisation, clear path for improvement
Transport to cells, and from cells to detector
E-field same as RT-edm; clear path forward to increase substantially
Proof-of-principle effective superconducting magnetic shielding
Reliable operation of solid-state detectors in LHe
Development of SQUID magnetometry system
Software, modelling, understanding systematics...
But...
Not modular enough. Turnaround too long; thermally inefficient
Constant race to make whole system work as proof-of-principle rather than focusing on small-scale key issues of transport and storage
Too ambitious for tiny group of people!

7. UK nEDM: The way forward
Two-pronged approach:
Short to medium term: Join PSI effort -
maintain world lead with incremental results
maximise return on former UK investment
Longer-term vision: Join new collaboration –
small-scale R&D
focus on specific problems at core of cryoEDM
retain leadership in ultimate sensitivity expt

8. PSI Using our old apparatus, but with improved systematics
This is the only nEDM experiment currently taking data
3E-25 ecm/day: approx same as us in ’02
same E, a; longer T but lower N
Problem with source D2 crystal (snow vs ice?) is limiting statistics; gradually improving
Expected results:
~ Factor 2 in 3 years
~ Factor 6 in ~6 or 7 years, from upgrade

9. New ILL-based collaboration
Collaboration just formed:
ILL: To develop new source, with magnetic confinement, on high-intensity custom beamline
Munich: High-quality magnetic shielded environment (with room-temperature experiment as staging post for ultimate cryogenic expt)
RAL/Sussex: Focus on cryogenic EDM insert to be put in magnetic shield.
Removes enormous drain of running source/shields
Focus exclusively on key areas, with much less effort
Realistically [my view!] 8-10 years before cryogenic experiment running.
Good match to PSI timescales.

10. Worldwide nEDM Searches
Back in ’02 it was just us. Now a very active field...
SNS
J-PARC
ILL
PSI
FRMII
TRIUMF
RCNP
PNPI

11. SNS Cryogenic experiment: LHe ~100 collaborators
UCN production within measurement volume – no separate source
Scintillation from 3He capture to measure precession frequency
~100 collaborators
Technically very challenging. Commissioning date slipped from 2012 (in ‘05) to at least 2020.
Recent DOE review: New project mgmt, focus on specific technical issues. Many tricky areas...
Aim: ~4E-28 ecm/yr. (Originally 5E-29 ecm.)

12. PNPI
Phase I at ILL. Aim ~1E-26 ecm; initial goal was to reach this level by Currently halted, restarting 2015.
Phase II: Large and well resourced facility being built at Gatchina, with solid D2 source. Aim ~1E-27 ecm. Timescale uncertain.

13. RCNP/TRIUMF UCN production in HeII, extraction to room-temp
Source intensity probably limited by heating
~30 collaborators
Phase I aim ~5E-27 ecm, but still quite some way from realisation
Eventually move to TRIUMF for ~5E-28 ecm?

14. Others
New effort just started at Los Alamos: room-temp experiment with Hg magnetometer. Will take several years.
JPARC: (33 collaborators) Solid D2 source under development; first calculations suggest 1E-27 ecm may be possible. In very early stages.
Crystal diffraction: JPARC, NIST. Early R&D work. Federov, PNPI, ongoing for some years; eventual stated goal 1E-27 ecm.

15. Electron EDM
Record was held by Hinds (IC) group, using YbF beam, until Oct 2013 overtaken by ACME collaboration (Harvard, Yale, UCLA...) using ThO.
Limit currently stands at
|de| < 8.7 x 10−29 e.cm
However, UK is not out of the race...

16. M R Tarbutt, B E Sauer, J J Hudson and E A Hinds
Proposed YbF fountain
Design for a fountain of YbF molecules to measure the electron's electric dipole moment
M R Tarbutt, B E Sauer, J J Hudson and E A Hinds
New J. Phys. 15 (2013) 4K
Fantastically inefficient: 10-8 from cell to detector. But T = 300ms, so 60 h of data gives sd = 3x10-31 e.cm!

17. EDM conclusion EDM physics of increasing interest worldwide
UK should capitalise on investment and maintain world lead
Science Board recognised that CryoEDM was too ambitious for small group to deliver; recommended joining or forming another int’l collaboration
Two-pronged approach:
PSI to maximise return on previous investment, and deliver incremental results in short-medium term
Small-scale R&D focusing on technical challenges of cryogenic experiment for longer-term sensitivity
eEDM: New approach offers prospect of regaining world lead.

18. spare slides

19. 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
We have demonstrated production rate consistent with anticipated.

20. UCN detection in liquid helium
Solid-state detectors developed for use in LHe
Thin surface film of 6LiF: n + 6Li  a + 3H

21. New beamline ILL funded (800 k€) Installation 2014
Should have 4x intensity
Need to characterise: intensity spectrum polarisation